Workshop Lighting - Warm White or Pure White?

[German_EE]

I have spent the weekend installing LED lighting, individual modules rather than strips. As an experiment I purchased a 50/50 mix of warm white and pure white units to see which I liked the best (current consumption is the same) but which do you prefer, warm white or the full on pure white units?

Note, this is for general lighting, for close up work I still plan to rely on a desk light with an adjustable stand.

[n45048]

I mentioned in a previous topic somewhere that I'm a fan of warmer light (around the 2700-3200K mark). I find fluro and pure white LEDs distracting and sterile.

If you're planning on taking photos or video, you can (and should) white balance anyway, so the colour of your lighting isn't going to matter too much.

Another forum member posted some details about his set up at: https://www.eevblog.com/forum/chat/cree-led-lighting-in-the-lab/

[8086]

I prefer to be able to adjust the temperature manually, between say 3000 and 5000K.

But then, I do work for a lighting controls company.

Failing that, I prefer to be towards the cool end of the spectrum normally, for a workspace environment.

[Zero999]

This is a personal preference thing.

I find the higher the colour temperature, the brighter the light needs to be. A high colour temperature but low intensity results in a horrible greyish coloured light.

In the lounge I like warm lighting, 2700K or less. For soldering I light slightly warmish 3000K to 3500K.

I dislike the really high colour temperatures such as 4500K or 5000K.

[Leiothrix]

5000K-ish.

I think people only like warm lights because they grew up with incandescents.

The colour is horrible, and makes everything else look horrible too.

During the day, go into a hallway and have a look at the light spilling out from a room.  If it's lit by a warm source you can see the orange glow, if it's ~5000K it looks like brighter daylight.

[rdl]

I like LED bulbs with the warmer incandescent type color for around the house. It probably does have something to do with growing up with that type of light.

If the light is too blue it becomes somewhat garish looking at night. It's not a bad choice for the workshop though, because it blends well with daylight fluorescents.

I think there were studies done for LED street lighting that recommended around 4300K, but no one seems to make that color. The Cree "daylight" bulbs I've bought are 5000K. They're not terribly blue, but I wouldn't want one in my bedside lamp.

[dannyf]

warm white or the full on pure white units?

1) incandescent;
2) incandescent;
3 more incandescent,
4) warm white if I have to use led lighting.

Pure white feels cold and reminds me of public bathrooms in India.

[marshallh]

Warm temps for me only. During the day cool light isn't bad, but at night it screws with your sleeping. There's been research done on lighting and its effects on circadian rhythms, which I have to agree with from experience.

5000K works for me. Cree is finally making decent LED replacements which are warm enough.

Ever since getting a program on my PC that tints the screen oranger at later hours to prevent eyestrain I'm a believer.

[RobertoLG]

for my tastes pure white is better

[IanB]

Most of this thread seems to be missing the most important thing. It's not about colour temperature, it is about colour rendition. In a workshop or any living space, it is best to have lighting that renders colours accurately across the spectrum so that things look natural and their details are clear. So look for lighting with a good CRI.

Colour temperature matters a lot less since the human brain will readily compensate for any general shift towards the blue or red end of the spectrum.

[n45048]

Warm temps for me only. During the day cool light isn't bad, but at night it screws with your sleeping. There's been research done on lighting and its effects on circadian rhythms, which I have to agree with from experience.

5000K works for me. Cree is finally making decent LED replacements which are warm enough.

Ever since getting a program on my PC that tints the screen oranger at later hours to prevent eyestrain I'm a believer.

I agree. There are plenty of studies which go towards proving that light around the blue bit of the spectrum is the worst offender at suppressing melatonin (although any light disrupts this). More recently, white LED's have been blamed for similar disturbances in sleep.

[GreyWoolfe]

Marshallh, are you using f-lux?  I use it on my laptop.  As far as lighting over my workbench/office desk/ham radio desk, I use Daylight Deluxe (6500K).  I tried warm white bulbs but didn't care for them at all.  I have a 4 bulb, 4 ft fixture over the center of the workbench and am very happy with the light I get.  The desks have 2 bulb 4 ft fixtures which is plenty.  All the fixtures are suspended from the ceiling at just enough height that I won't hit my head on them when standing or leaning over the desks.  We do use cooler CFL bulbs in the lights in the rest of the house and I am fine with it.  I just like the 'brighter' or harsher (which ever term you prefer) white of the daylight deluxe bulbs while working.

[gxti]

No idea on shop lighting. I was using a "daylight" CFL for a while in my work area and was happy with that. I tried out some 2700K LEDs I bought for other areas and found it was harder to resolve details even with more watts but it could have been incidental.

Someone beat me to it on the sleep disruption, but here's a source:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2831986/

In one experiment, Kunz showed that exposing healthy subjects to 30 minutes of 500 lux polychromatic blue light an hour before bedtime, in their natural home environment, delayed the onset of rapid eye movement sleep by 30 minutes. The implications of that finding have yet to be determined, says Kunz. But the melanopsin receptors are particularly sensitive during the evening and nighttime hours, so “I’m pretty sure that at least many of the sleep disorders we are facing epidemically are related to evening or nighttime light,” he says. According to the National Center on Sleep Disorders Research, sleep-related problems affect 50–70 million U.S. men and women of all ages.

Which isn't to say you shouldn't use it in a shop, but definitely not in your living room.

[nanofrog]

FWIW, I've found I prefer mine in the 5000K range (daylight, ~ noon IIRC). The unfortunate side, is this seems to be more difficult to find, and tends to be more expensive when you do.

Warmer, say 3000 - 3200K is fine for normal household lighting is fine (i.e. concerned about tripping over the cat, finding my way to the kitchen, ...). No pain at any rate, but not wonderful for fine detail IME. For detailed work such as soldering, probing and such on an electronics bench, warm doesn't cut it for me. And the bluish shade of 6000 - 6500K I don't care for at all (actually causes me some eye strain/pain, and will develop into headaches if I don't get away from it). Discovered by accident per se, that 5000K works best for me (literally grabbed the wrong bulb once, and been hooked ever since).

YMMV though, and as mentioned is subjective. 

[rdl]

FWIW, I've found I prefer mine in the 5000K range (daylight, ~ noon IIRC). The unfortunate side, is this seems to be more difficult to find, and tends to be more expensive when you do.

If you live near a Home Depot go get some of the Cree "Daylight" LED bulbs. They're 5000K, well made, and relatively cheap. I have several of the 1100 lumen ones over my bench and I really like them. I think they were around $15 and they've been in use for many months now.

I have 5 or 6 of the Cree bulbs in my small apartment now, and I've been very happy with them, though most are the warmer 2700K version. Only above my bench do I use the 5000K, because I also have a daylight fluorescent lamp in there and the colors blend together well.

[nanofrog]

If you live near a Home Depot go get some of the Cree "Daylight" LED bulbs. They're 5000K, well made, and relatively cheap. I have several of the 1100 lumen ones over my bench and I really like them. I think they were around $15 and they've been in use for many months now.

Thanks. 

I've actually seen them not too long ago, and the price was definitely attractive (saw 40W & 60W incandescent bulb equivalents were $10 per). 

Definitely down from what I paid about 1 - 1.5yrs earlier for ~500 lumen Utilitech spot lights at Lowes ($30 per).

Got some 5000K LED light strip for under shelving lighting, and that particular color temp was still more expensive than the warm or other cool color strips at the time (few months ago). Same for other bulb formats (hadn't yet decided on LED strip, MR16, ...). Definitely consistency regarding 5000K daylight (lot less of it available vs. 6000 - 6500K).

Standard CCFL overheads for the room round it out (warm).

[Zero999]

Most of this thread seems to be missing the most important thing. It's not about colour temperature, it is about colour rendition. In a workshop or any living space, it is best to have lighting that renders colours accurately across the spectrum so that things look natural and their details are clear. So look for lighting with a good CRI.

Colour temperature matters a lot less since the human brain will readily compensate for any general shift towards the blue or red end of the spectrum.

I agree with you about CRI but in my experience, colour temperature does make a difference to that too.  Assuming an ideal black body emitter, low colour temperature light suppresses the blue end of the spectrum and high colour temperature suppresses the red.

[G7PSK]

Day light. Nothing beats it.

[cimmo]

In working areas I prefer a mixture of warm white and cool white LED lamps.
About 50% to 75% warm.
You get the best of both worlds, and the resultant CRI from the mix subjectively appears smoother. (One of my hobbies involves mixing paint and some nasty LEDs have big holes in the emitted spectrum. You find this out when you view the mixed paint in the sun/daylight.)
For close up work a "pure" (4000-5000K) spot lamp is preferred.

[Dave Turner]

It also depends on whether your lab has natural daylight available and if so how much.

In a naturally lit lab supplementary lighting should match daylight as closely as possible otherwise the contrasting colour temperatures can be off-putting. Given that daylight varies throughout the day and due to weather conditions the daylight "bulbs" have to be a compromise, but are in my opinion, the best option.

In an enclosed environment I would also choose daylight bulbs for a lab, round the workspace at the very least.

Warm white is restricted to my bedroom and living room.

But, hey, that's my opinion based on research done for a number of labs I designed in the 80's.

[SteveyG]

Daylight LED is best for the lab. Best colour rendering and less heat than incandescent, plus more reliable. Strips are good for reducing shadows and directionality.

Not true at all. CRI and Colour Temperature are not directly linked and incandescent lamps actually have a CRI of 100.

[owiecc]

[...] incandescent lamps actually have a CRI of 100.

They have CRI = 100 because of the way CRI is calculated. However, CRI is a very bar color quality index. There have been many other proposals,but not one is a standard yet. There can be different types of spectra that are more pleasing to the eye than the blackbody type.

It all depends on culture and what you are surrounded with. If you live in the far north/south, you will most likely prefer lower CT. In hot countries, like Brazil, you will prefer higher CT. If you are surrounded with a lot of saturated colors  and organic materials you may need more continuous lights spectrum. Scandinavians may not need that.

[Zero999]

[...] incandescent lamps actually have a CRI of 100.

They have CRI = 100 because of the way CRI is calculated. However, CRI is a very bar color quality index. There have been many other proposals,but not one is a standard yet. There can be different types of spectra that are more pleasing to the eye than the blackbody type.

It all depends on culture and what you are surrounded with. If you live in the far north/south, you will most likely prefer lower CT. In hot countries, like Brazil, you will prefer higher CT. If you are surrounded with a lot of saturated colors  and organic materials you may need more continuous lights spectrum. Scandinavians may not need that.

Exactly, as I said in my previous post, a CRI of 100 doesn't mean it gives the best colour rendition. It's just a calculation.

[denelec]

Cool white for work.
Warm white for leisure.

And candlelight for quality time with your significant other...

[EEVblog]

This is a personal preference thing.

It's more than that, it's a lifetime of indoctrination from lower temperature lights.

[SteveyG]

Not true at all. CRI and Colour Temperature are not directly linked and incandescent lamps actually have a CRI of 100.

Which is wonderful if you like everything to be a bit yellow, but if you like accurate colour then LED daylight is better.

Why state that the LEDs have better colour rendering then? I'd also disagree with your comment about reliability. How many 'unreliable' incandescent lamps or even fluorescent lights do you encounter? I have some Philips MR16s that are 16 years old, and fluorescent strip lights that are a similar age.

Personally I find a good set of tri-phosphor tubes in my lab to be excellent, with local clamp on style lamps for close illumination. LEDs sold as daylight (~6000K) are generally the wrong colour temperature for accurate colour as the blue content is too high and lack the distinct peaks you'd find from a tri-phosphor tube. Between 4300K and 4800K is typically optimal as with TVs and projectors etc. 

[Zero999]

This is a personal preference thing.

It's more than that, it's a lifetime of indoctrination from lower temperature lights.

No, it's just natural to have lower temperature lights in more relaxing environments such as the lounge and bedroom. It probably goes back further than incandescents, when people had to light fires for light.

Of course in a working in environment, higher colour temperature light, as near to daylight as possible is preferable to most people.

It's just bad to have high colour temperature installed everywhere, especially in the bedroom it can cause health problems. It's just not natural to be exposed to daylight 24/7.

The problem with the supposed daylight simulation lamps is they're not light daylight, as there's a huge peak in the blue part of the spectrum, a dip just between the blue and green and a cut off in the orange end of the spectrum, leaving reds suppressed. It's also no where near bright enough, so tends to look dull and greyish rather than true white.

[IanB]

Why state that the LEDs have better colour rendering then?

Because they do? CRI is based on incandescent bulbs, not on how well a certain light renders certain colours. I think you are confusing the two.

I'd also disagree with your comment about reliability. How many 'unreliable' incandescent lamps or even fluorescent lights do you encounter? I have some Philips MR16s that are 16 years old, and fluorescent strip lights that are a similar age.

Anecdotal evidence. The LED bulbs I buy have a five year warranty, and most incandescents are rated for less than that if you use them regularly (1000 hours). There is also the rather low on/off cycle limit, compared to 50k typical on LEDs. Fluorescent lights fail al the time, we have the ones in our office replaced regularly and they flicker badly, but I can't be bothered to look for data right now.

Do you have any data that contradicts this?

CRI is "Colour Rendering Index". It is based on how well a light source renders colours. A high CRI lamp will have a balanced output over the whole light spectrum without any pronounced peaks or valleys at any particular frequency.

I have many incandescent bulbs in my house that have been installed for over ten years and used daily without replacement. When you can say the same thing about CFL or LED lamps then we can talk.

[SteveyG]

Because they do? CRI is based on incandescent bulbs, not on how well a certain light renders certain colours. I think you are confusing the two.

Think about what you're saying for a moment. CRI is high for an incandescent lamp because they emit a broad spectrum of light across the entire visible range.
An LED generally has a blue spike and a peak around yellow which fools the eye into thinking it's white light, but colours between the blue peak and yellow peak and colour above the red peak will never be as well rendered unless the spectrum is broadened.

[Zero999]

CRI is "Colour Rendering Index". It is based on how well a light source renders colours. A high CRI lamp will have a balanced output over the whole light spectrum without any pronounced peaks or valleys at any particular frequency.

I have many incandescent bulbs in my house that have been installed for over ten years and used daily without replacement. When you can say the same thing about CFL or LED lamps then we can talk.

Well if you hardly ever run them at full brightness, then incandescents will last for a long time but they still costed you much more in electricity than the equivalent CFL.

Because they do? CRI is based on incandescent bulbs, not on how well a certain light renders certain colours. I think you are confusing the two.

Think about what you're saying for a moment. CRI is high for an incandescent lamp because they emit a broad spectrum of light across the entire visible range.
An LED generally has a blue spike and a peak around yellow which fools the eye into thinking it's white light, but colours between the blue peak and yellow peak and colour above the red peak will never be as well rendered unless the spectrum is broadened.

For a start. Not all CFLs and LEDs are created equal. Some have a better spectrum than others. It depends on the LED dies and or phosphors used. Some LEDs have excellent colour rendering properties because they include a red die, in addition to the usual blue LED and phosphor.

There may be no peaks or valleys in the output of an incandescent. The spectrum may be consistent across the visible range with no peaks or troughs but it doesn't change the fact it is deficient in the shorter wavelengths, making blue objects appear more black.

[SteveyG]

CRI is "Colour Rendering Index". It is based on how well a light source renders colours. A high CRI lamp will have a balanced output over the whole light spectrum without any pronounced peaks or valleys at any particular frequency.

I have many incandescent bulbs in my house that have been installed for over ten years and used daily without replacement. When you can say the same thing about CFL or LED lamps then we can talk.

Well if you hardly ever run them at full brightness, then incandescents will last for a long time but they still costed you much more in electricity than the equivalent CFL.

I don't think he said anywhere he wasn't running them at full brightness? I've never used dimmer switches yet the incandescents have lasted an order of magnitude longer than a lot of the CFLs that I've used, including some £10/pc Sylvania ones.

I have some T5 fittings in the workshop that have Philips 93CRI lamps in them, but the control gear has failed twice (£90 each) which have offset the cost savings... They are great tubes though.

 

[Zero999]

I don't think he said anywhere he wasn't running them at full brightness?

It was in a different thread:
https://www.eevblog.com/forum/beginners/ac-soft-start-incandescent-lamp-switch/msg336720/#msg336720

The modern world is making it very difficult to have controllable lighting. Every light in my house is on a dimmer switch, and I run all my lights at 1/3 to 1/2 brightness. Putting the lights on full power now results in an "Ow! My eyes!" level of brightness.

Sadly, CFLs are invariably not dimmable (and the light has a horrible colour). LED lamps are sometimes dimmable, mostly not, but are hugely expensive. The halogen replacements for regular incan bulbs are not dimmable either. Halogen lamps need to be run at near full power to work properly. I have read that if you dim them they will have a shorter lifetime.

Fortunately I have found that bulbs run at half brightness last for years, so I can stockpile spare bulbs.

I've never used dimmer switches yet the incandescents have lasted an order of magnitude longer than a lot of the CFLs that I've used, including some £10/pc Sylvania ones.

I have some T5 fittings in the workshop that have Philips 93CRI lamps in them, but the control gear has failed twice (£90 each) which have offset the cost savings... They are great tubes though.

Yes, ballasts often go, quite often due to crappy capacitors. The lifetime is an average. It's a pain when things fail early but it doesn't mean it's the norm.

[IanB]

I don't think he said anywhere he wasn't running them at full brightness? I've never used dimmer switches yet the incandescents have lasted an order of magnitude longer than a lot of the CFLs that I've used, including some £10/pc Sylvania ones.

I do run them on dimmers--every light fixture in my house has a dimmer switch. Also, all of the light fixtures use special decorative bulbs of various kinds that are not replaceable with CFLs--CFLs don't fit.

[SteveyG]

You can't really buy high wattage incandescent bulbs in the EU any more, but if the OP can then maybe he should try comparing. Having said all that, the form factor of LED strips, or having lots of lower wattage LED bulbs distributed around the area and not producing too much heat, is likely to outweigh whatever preference an individual might have for incandescent lighting.

The trouble is, the LED strips and LED bulbs are usually the worst LEDs money can buy with rapidly degrading phosphor etc. If you'd said you'd made your own lights using high quality LEDs, or even better used something like a cluster of coloured Luxeon Z's with the all important 'lime' colour for filling in that area that's usually missing on white LEDs I could quite believe that they'd be preferable to other lighting sources.

[Zero999]

I don't think he said anywhere he wasn't running them at full brightness? I've never used dimmer switches yet the incandescents have lasted an order of magnitude longer than a lot of the CFLs that I've used, including some £10/pc Sylvania ones.

I have some T5 fittings in the workshop that have Philips 93CRI lamps in them, but the control gear has failed twice (£90 each) which have offset the cost savings... They are great tubes though.

Just thinking, you can protect yourself against this. When you fit the new lamp/ballast, then write the date on it and keep the receipt somewhere safe, possibly rolled in a small tube and stuck to the fitting. Then if it fails too so, go back to the retailer for a refund.

[ConKbot]

3500-4500k in office areas, 4000-5500k in lab/work areas, with ether good fluro tubes, (if work is paying for it, https://www.1000bulbs.com/product/4722/F-32T8TL950P.html it its your own pocket, https://www.1000bulbs.com/category/f32t8-fluorescent-tubes-5000k-800-series-phosphors/ ) or LED with a CRI > 80, ~500 lux for office areas, ~2-3000 lux for general work benches, and 10k lux on a soldering station or something with equally small parts.  Along with the expectation that anything you pick up for cheap will probably be constructed equally cheap.  ( '5000' lumen LED bulb thats 6500k, and costs $5.99 online?  Its probably going to be a lovely shade of blue, or blue-green)

[Zero999]

I don't think he said anywhere he wasn't running them at full brightness? I've never used dimmer switches yet the incandescents have lasted an order of magnitude longer than a lot of the CFLs that I've used, including some £10/pc Sylvania ones.

I do run them on dimmers--every light fixture in my house has a dimmer switch. Also, all of the light fixtures use special decorative bulbs of various kinds that are not replaceable with CFLs--CFLs don't fit.

These look good. It's compatible with a fairly wide range of dimmers and the colour temperature reduces when dimmed. They need to work on the aesthetics though.
http://www.lednovation.com/products/BR30_LED.asp

[Kjelt]

These look good. It's compatible with a fairly wide range of dimmers and the colour temperature reduces when dimmed. They need to work on the aesthetics though.
http://www.lednovation.com/products/BR30_LED.asp

Great so you have a new technology capable of much more than the old technology but you are now handicapping it to mimic the old technology, what a waste.
This is the same as that you add a noise and tick circuit to your streamer or other digital audio source because you liked that soo much on your record player.
If you want or need tunable white light sources buy a true tunable white light source. But for most people (as tests showed) they only need one colour for their workbench in the living room it is another story.

[steve30]

Warm white or cool white? Its hard to say for LEDs.

I have a fluorescent fixture with a dimmable ballast and a selection of tubes, so I can choose the colour temperature, CRI and brightness depending on what mood I'm in, what work I'm doing, the time of year etc.

Personally I've found warmer whites preferable in winter, and cooler whites preferable in summer. I do tend to find around 4000k to be a good compromise for most of the year. If I were choosing LEDs, I'd probably choose 4000k. I currently have 4000k fluorescent tubes, but I might change them back to 5400k in summer.

I recommend trying out different types and seeing what you like best .

[dannyf]

Even the warm whites may not be warm enough: I have to use a reddish shape on mine as they look too "cold" for me.

Every year, I do two lamp changes: incandescents to CFLs at the beginning of the summer and then CFLs to incandescents at beginning of the winter, trying to minimize my energy consumption,

[Artlav]

3000K LEDs in the evening or at night.
Cozy, pleasant light.

4200K Metal Halides at 2000 lux for work/filming/overcast winter days.
Look like sunlight not in early evening, banishes sleepiness and boosts the mood during winter (also good for seeing tiny details).

I tend to find low temperature light pleasant - the long, cold filament incandescent bulbs feel almost like fire, like candles.
Good light to think under.

[SteveyG]

Make your own. 

[Zero999]

Every year, I do two lamp changes: incandescents to CFLs at the beginning of the summer and then CFLs to incandescents at beginning of the winter, trying to minimize my energy consumption,

Although incandescents do contribute to heating your home in winter, I hope you're aware that it's less efficient than using a fuel such a natural gas or a heat pump, so unless you've got resistive heating (if so, it's probably a worthwhile investment upgrading), it's cheaper to keep the CFLs in all the time.

[ConKbot]

Every year, I do two lamp changes: incandescents to CFLs at the beginning of the summer and then CFLs to incandescents at beginning of the winter, trying to minimize my energy consumption,

Although incandescents do contribute to heating your home in winter, I hope you're aware that it's less efficient than using a fuel such a natural gas or a heat pump, so unless you've got resistive heating (if so, it's probably a worthwhile investment upgrading), it's cheaper to keep the CFLs in all the time.

Cost efficient, yes most definitely, its almost a shame to use electricity for heat in any application that doesnt need precise control.  Actual efficiency, a high end condensing natural gas furnace could be at most on par with the light bulbs (~98% efficiency) Vs the heat pumps which are way over 100% efficiency. (And now the physics and thermo people get a  bit of an eye twitch  )   


Now for the thermo

[Alisa]

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[KL27x]

I put a brighter but whiter flourescent bulb in my mag lamp at one point. I liked the color and the increased brightness, but I went back to the dimmer, yellow, fuller spectrum bulb. Even though it looks way dimmer, I found there was significantly less eye strain when I was working on small things.

I tried upgrading to a bright white LED mag lamp that had more lumens, but that was even worse. To be fair, I'm not sure what was worse between the color or the insufficient diffuser.  I repaired my flourescent mag lamp for the 4th time and put the LED lamp in the garage.

I also still use a halogen lamp. I repaired it when the lamp broke and swapped some parts out with a modern bulb lamp. They still sell the halogen bulbs, but the halogen lamps are no more for sale, here, due to being a fire hazard.

Now that I use the stereomicroscope for detail work, I don't really care so much about my general lighting. Whiter light appears brighter and does seem to have a positive effect on my mood.

[Simon]

I have spent the weekend installing LED lighting, individual modules rather than strips. As an experiment I purchased a 50/50 mix of warm white and pure white units to see which I liked the best (current consumption is the same) but which do you prefer, warm white or the full on pure white units?

Note, this is for general lighting, for close up work I still plan to rely on a desk light with an adjustable stand.

I prefer white. Warm white is a joke, it is actually yellow and your eyes auto white balance to make it look white (your brain does actually). I have visual stress and find yellow/red annoying so tend to prefer Bluer lighting. 4200K absolute minimum, preferably 5500K.

LED lights have been a miracle to my life and I was really really happy when the office lights at work got changed for white LED. I even tend to reduce the RED on my monitors but that is just me.

I think the term warm white was a bit of marketing to cover the fact that getting a white light once was not cheap or possible.

[Calambres]

I find the higher the colour temperature, the brighter the light needs to be.

Many years ago, while reading about the yellow front lights in french cars, the author stated that the reason behind that colour selection was based upon a study that found  the human vision to be more sentitive to lower colour temperature, that is, you need less watts of yellow light to "see" the same amount than that of a standard incandescent light. That may well be the reason behind your perception.

Personally, I cannot stand the white leds. I hate them. Don't know why but that kind of light makes me feel very uncomfortable.

[Simon]

I think beyond 4200K all lights start to look positively white and after 5500K it is going into blue, again our brains correct. I suspect that although every one differs in their individual perception there will be a range of colour that the brain can adjust for after which it becomes a problem with skewed colours. I am specifically skewed to over reacting to red so blue is good for me as it put's in the necessary offset. My minimum requirement to see a light as white is 4200K, I can tell you the colour temperature of lights between 2700 and 4200K as i can see their actual colour, but even I dislike too much blue.

[Synthtech]

I can’t deal with hard “daylight” temperature fluorescent lighting or CFL’s in my workspace, they are too actinic, they feel like the lighting equivalent of listening to an MP3.

The exception being that I keep a very bright daylight LED arm mounted lamp at each work area so that when I need that hard white light with too much blue in it for certain jobs it’s right there.

Don’t even get me started about low quality domestic CFL spiral bulbs that have too much green in their spectrum.

[Simon]

i think the problem is that fluorescent technology cannot easily achieve the right light colour. That is why LED's are a godsend for me as they tend to be bluer anywag but they also have a fuller bodied white daylight colour. I have tried daylight CFL's and they were awful producing low light levels as they clearly lack some vital colour although were white enough for me to see as whiteish they did not seem to actually illuminate.

4200K I think is the limit for CFL, 3500K was actually tolerable. I think 2700K was a catchall classification for any old shit that was just yellow in colour but they only had the 2700K box to tick.

[nctnico]

Look at CRI numbers when buying CFL. Some are quite good (like Philips TLD mast 900 series) but you likely don't find these in the local hadware store.

[Psi]

I tried two 50W 5600k YUJI leds in my lab, quite nice but i think it would be better a little warmer.

They only make 5600k and 3200k in the 50W package so i think what i'll do is get a pack of 3200k (they come in lot of two).

Then i can swap one 5600k in the lab with a 3200k.
That should give be 100W at around 4000k.  I can also dim one to get some color temp adjustments if needed.

[Kjelt]

Rule of thumb for most consumers:

2700K very warm white   Kitchen / Bedroom
3000K warm white          Living Room / Bedroom
4000K white                   Workplace / Study/ Office / Machinery
5000K + above               If needed for color matching or plants etc. etc. not preferred for normal consumers.

If you need different kinds of white on the same spot during the day for instance in the living room / study  or bedroom there are "tunable white" fixtures that let you choose between 2700K and 4000K. These usually have 2700K and 4000K leds and two drivers that dim according to the setting.

[rdl]

The vast majority of the economical. single color bulbs are either 2700K (or thereabouts) or 5500K. I really don't understand the lack of variety. The 2700K is fine for living areas, but a bit too yellow for anything else. They obviously chose this color so the new LED "bulbs" would look like incandescent. As far as I'm concerned, 5500K is just about too blue for anything. I've seen 3000K becoming more common, but I found that still too yellow for my work area. I finally found some 4000K "shop lights" and they're pretty good, but I haven't seen that color in bulb form.

[Simon]

Yea, we finally found a better technology than CFL and use it to replicate the main defect of CFL, carry on making yellow lights. Personally i suspect that many CFL's marketed as 2700K were below.

[GreyWoolfe]

I have spent the weekend installing LED lighting, individual modules rather than strips. As an experiment I purchased a 50/50 mix of warm white and pure white units to see which I liked the best (current consumption is the same) but which do you prefer, warm white or the full on pure white units?

Note, this is for general lighting, for close up work I still plan to rely on a desk light with an adjustable stand.

I prefer white. Warm white is a joke, it is actually yellow and your eyes auto white balance to make it look white (your brain does actually). I have visual stress and find yellow/red annoying so tend to prefer Bluer lighting. 4200K absolute minimum, preferably 5500K.

LED lights have been a miracle to my life and I was really really happy when the office lights at work got changed for white LED. I even tend to reduce the RED on my monitors but that is just me.

I think the term warm white was a bit of marketing to cover the fact that getting a white light once was not cheap or possible.

I'm with you.  I had fluorescent over my workbench.  I now have 5,000K 6 bulb LED fixtures and I am much happier with my lighting.  Very bright on my bench but doesn't wash out the displays on all the toys or the monitor.  All the other lights in my office are now also LED so the savings on the electric bill are a bonus above me seeing better.

[Simon]

Well LED's are being praised for the reduction in power usage in the UK. I think realistically it's a mix of all commercial items being more and more efficient either to suit regulations or as a natural evolution of electronics.

Of course the media are ignorant. I use the same wattage in LED than CFL. I am just happier.

[coppice]

i think the problem is that fluorescent technology cannot easily achieve the right light colour.

The light output from fluorescent lights has one serious drawback - the two main mercury lines are suppressed by the envelope, but are still quite strong in the output spectrum. Apart from that, the colour is as good as you pay for. Tube makers typically produce 20 or more finely tuned colour profiles for a range of applications, but most places just stock a vaguely daylight and a vaguely warm white colour. These are quite high efficiency, and have a pretty reasonable spectrum for general purpose applications. Tubes from good makers are constantly monitored to ensure the spectrum of the phosphor mix stays within fairly tight limits. At the other extreme, the colour usually called "graphic" is intended for graphic arts applications. It has a more tightly controlled spectrum, thicker glass to suppress the mercury lines more, but rather poor efficiency.

If, say, a clothing store buys the wrong tubes, they get a flood of "it didn't look this colour when I bought it" returns, so they are very sensitive to fluorescent tubes being accurate. When I did a summer job in Thorn Lighting's colorimetry lab in the 70s, a purchasing executive at M&S was fired for screwing up their group wide lighting orders, because of the flood of returns it caused.

[Edison]

At work is the most suitable daylight that is about 4000K
When using 2700 - 3000K (light bulb), more power is required for the same luminosity as 4000K.
6000K light is not suitable for work - tired eyes.
It is important however CRI (CRI - color rendering index) for our purposes should not be less than 85

[Kjelt]

Yea, we finally found a better technology than CFL and use it to replicate the main defect of CFL, carry on making yellow lights. Personally i suspect that many CFL's marketed as 2700K were below.

Sorry this is a nonsense statement. The drawback of CFL was not the colourtemperature because you could choose that such that all colours even RGB were available. I can't help you never went further than your supermarket to get a CFL.

The main drawback of CFL was with cold temperatures problems starting, the older ones with the copper/iron ballast were getting a bit hot and when the starter was older had also problems igniting. But the modern TL5 for instance with electronic drivers can still compete with Led and is in many cases superior to cheap led fixtures from the far east.

The biggest advantage for LED over CFL is dimmable and lifetime,
CFL's have big issues when dimmed <10%, the filaments then get more current to compensate for the colder plasma and shorten their lifespan significantly.

[Simon]

my personal experience with CFL that they were yellow, or yellow or yellow or grey but called "daylight" and needed to be 2x the power to see by. Yes I searched. Most vendors won't even tell you the colour temperature.

[Edison]

The biggest advantage for LED over CFL is dimmable and lifetime,
CFL's have big issues when dimmed <10%, the filaments then get more current to compensate for the colder plasma and shorten their lifespan significantly.

CFL are dimmed by special ballasts, start at 100% and then dim the brightness - very short action

[Kjelt]

The biggest advantage for LED over CFL is dimmable and lifetime,
CFL's have big issues when dimmed <10%, the filaments then get more current to compensate for the colder plasma and shorten their lifespan significantly.

CFL are dimmed by special ballasts, start at 100% and then dim the brightness - very short action

Yes there are three currents , two through the filaments used for pre heating and during dimming and one through the plasma after ignition.
My point if you dim a cfl below 10-15% the current through the plasma reaches a critical point where the plasma cools to much down to keep the arc going and it will shutdown. To mitigate the currents through the filaments are increased compensating for the plasma drop in temperature. Side effect the lifespan decreases significantly.
TL lights that have a EOL of 20000 hours when not dimmed can drop to 2000 hours if continuously dimmed below 10%.

[Edison]

I use industrial LED strip 24V  14W/m  4000K  2700lm/m  CRI 90  (1x1,5m + 1m) is not-dimmable - each cut has  current source instead of  resistors
I have my own sun 

[aix]

I've been experimenting with IKEA Trådfri "white spectrum" LED lights. They're switchable between 2200K, 2700K and 4000K.

The first impression is pretty good, although the jury is still out on whether wireless (ZigBee) control is a good idea.

Examples:

• https://www.ikea.com/gb/en/products/lighting/smart-lighting/tr%C3%A5dfri-led-bulb-e27-980-lumen-wireless-dimmable-white-spectrum-opal-white-art-10318263/
• https://www.ikea.com/gb/en/products/lighting/ceiling-lights/floalt-led-light-panel-w-wireless-control-dimmable-white-spectrum-art-40332210/

[Brumby]

I found some 4100ºK CFLs worked for me for my purposes.  No idea of the CRI, but works for general task lighting and photography.  My photographic setup is for internet publication - so colour accuracy is a bit of a crap shoot once it is published, but up until then, I have been able to get acceptable results.

Saw them on a clearance special a few years ago, so I stocked up.  No plans on reviewing the lighting until the stock levels dwindle or some major opportunity presents itself.

Rule of thumb for most consumers:

2700K very warm white   Kitchen

Oh hell no.  The kitchen is the most dangerous room in the house - proper task lighting is essential.  Start at 4000ºK and go up.

[maginnovision]

I use 5000k pretty much everywhere.

[KL27x]

my personal experience with CFL that they were yellow, or yellow or yellow or grey but called "daylight" and needed to be 2x the power to see by

This is exactly my first impression. But when looking at tiny detais - say, soldering and inspecting a PCB -  I found that even with "half the light," the warm spectrum CFL does a better job for my eyes.

Many people do most of their work on a computer and through paperwork. I am terrible with (wanting to do) paperwork. Maybe it's my lighting.

I think perhaps when viewing physical 3 dimensional objects made of composite materials, a narrow spectrum light (brighter/whiter CFL/LED) maybe has more extreme constrast variation. As in some materials/surfaces/angles will reflect much more of this narrow bandwidth of light than other materials/surfaces/angles. And with a warmer, fuller spectrum, you get a more consistent contrast without the hot spots and relative dim spots that cause the eye strain.

[Red Squirrel]

I prefer "cool white" or "daylight", at least for when I need general lighting.  I find for the same lumens, it is brighter than warm white. 

For stuff like Christmas lights or other "decorative" lighting or living room, etc then warm looks better.

I also have a theory, it's totally from a non medical background so no idea how accurate it is, but I think if you go with "daylight" it may even improve mood and help you be more productive.  This theory is not really based on anything other than some research on depression when I went through it, and it talked about blue light helping seratonin levels.  Daylight bulbs will have more blue in it.  When I redo my office/lab lighting I might actually add blue LED strips too that I can switch separately.  Probably going to go with T8 bulbs, I find LED fixtures a bit limiting as you can't really pick the color temperature.   Ex: the fixture you like may not come in the color temperature you want.  Most of the ones at Home Depot are warm white.

[Red Squirrel]

I found some 4100ºK CFLs worked for me for my purposes.  No idea of the CRI, but works for general task lighting and photography.  My photographic setup is for internet publication - so colour accuracy is a bit of a crap shoot once it is published, but up until then, I have been able to get acceptable results.

Saw them on a clearance special a few years ago, so I stocked up.  No plans on reviewing the lighting until the stock levels dwindle or some major opportunity presents itself.

Rule of thumb for most consumers:

2700K very warm white   Kitchen

Oh hell no.  The kitchen is the most dangerous room in the house - proper task lighting is essential.  Start at 4000ºK and go up.

Bad lighting in kitchen may also make it harder to judge if food is cooked properly.

[KL27x]

White light should contain a full spectrum of colors, shouldn't it? How is it that "white light" is a narrower spectrum than "yellower" light? Or do I have it wrong?

Maybe it's that the most efficient CFL/LEDs in terms of lumen output are highly efficient because they use a narrow bandwidth that happens to be good at this metric. So high output, brighter lights tend to be narrower spectrum?

[Kjelt]

Rule of thumb for most consumers:
2700K very warm white   Kitchen

Oh hell no.  The kitchen is the most dangerous room in the house - proper task lighting is essential.  Start at 4000ºK and go up.

Yes for the workbench where you cut the food etc. I was just saying that an average customers esp. women want a cosy yellowish light in the kitchen, that pro chefs in their pro kitchen use 4000K is because it is a workplace for them 

[Kjelt]

White light should contain a full spectrum of colors, shouldn't it? How is it that "white light" is a narrower spectrum than "yellower" light? Or do I have it wrong

Read this and be enlightened 
https://en.wikipedia.org/wiki/Black-body_radiation

[Brumby]

Rule of thumb for most consumers:
2700K very warm white   Kitchen

Oh hell no.  The kitchen is the most dangerous room in the house - proper task lighting is essential.  Start at 4000ºK and go up.

Yes for the workbench where you cut the food etc. I was just saying that an average customers esp. women want a cosy yellowish light in the kitchen, that pro chefs in their pro kitchen use 4000K is because it is a workplace for them 

We may have to agree to disagree on the preference of the "average customer".

I would like to introduce you to the keeper of the kitchen here....

I installed a 2m strip of 5000ºK LEDs above her main work area with a couple of cable ties as a temporary setup to see if she liked it.  That was over a year ago - and I haven't been allowed to take it down in order to make a more permanent solution.

[Kjelt]

We may have to agree to disagree on the preference of the "average customer".

No problem for me, I am just quoting the outcome of marketing research from a previous company I worked for.
There are always people with other tastes.
Statistics 101 , a single sample/customer does not significantly change the outcome of the average if the sample size was big enough.

Second colour temperature ^oK says nothing about Lumens. Yes the higher the colourtemperature and fixed Wattage the Lumens will increase but increasing Wattage also increases Lumens.
Mistake nr1 is to place warm white yellowish light but too low Wattage, you are then comparing apples with pears (dutch expression in english probably some other fruit is applicable).
My advice is to place a dimmable Led fixture with enough Lumens and use it at the appropriate levels. You can cut your food excellent with enough Lumens to have good contrast. You don't need 4000K for that. For pro kitchens and workareas 4000K is preferred because it keeps the concentration higher due to the more blueish component in the light where humans have a weakness for. (simply said: reddish/yellowish light people think it is the end of day and go to sleep mode, blueish light people wake up and have better concentration. This is also scientificly proofed and tested and applied in schools and hospitals BTW so don't think I am making this up).

Besides there are many functions in the kitchen, many people besides cooking eat their meal in their kitchen and there is this show/display function.
I am not sure how many people like to enjoy their dinner with 5000K lighting , even worse MacDonald and other fastfood restaurants have used this cold light to make sure customers don't spent too much time there

[nfmax]

Mistake nr1 is to place warm white yellowish light but too low Wattage, you are then comparing apples with pears (dutch expression in english probably some other fruit is applicable).

In (British) English we say "comparing apples with oranges", so it's understandable why it would be different in Dutch

[Simon]

I have heard people use apples and pears in the UK as well.

[Kjelt]

Mistake nr1 is to place warm white yellowish light but too low Wattage, you are then comparing apples with pears (dutch expression in english probably some other fruit is applicable).

In (British) English we say "comparing apples with oranges", so it's understandable why it would be different in Dutch

Ah yes, still I am puzzled why, since there are not many orange trees growing in the UK ..........  oh well back on topic 

[Brumby]

We may have to agree to disagree on the preference of the "average customer".

No problem for me, I am just quoting the outcome of marketing research from a previous company I worked for.
There are always people with other tastes.
Statistics 101 , a single sample/customer does not significantly change the outcome of the average if the sample size was big enough.

Yeah, OK.  I acknowledge my statistical error - three sigma seems so far away.


But I'm still not touching that kitchen light.

[coppice]

I have heard people use apples and pears in the UK as well.

In English, apples and pears is rhyming slang for stairs. Its not a comparison metaphor. Its only some mainland languages which compare apples with pears.

[Simon]

Ah yes and knowing me I am going around talking about comparing apples to pears

[Edison]

In the Czech Republic also apples / pears   

[soldar]

Yea, we finally found a better technology than CFL and use it to replicate the main defect of CFL, carry on making yellow lights. Personally i suspect that many CFL's marketed as 2700K were below.

I agree with you in general terms. I have recently replaced a lot of CFLs with LED fixtures and the difference is astounding. The CFL were nominally 2K7 while the LED are 4K. The power draw is about the same or slightly less for the LEDs and yet the perception is that there is a lot more light. In the kitchen, the bathrooms, the working are, it feels SO much better and brighter.

But maybe there are places, like the bedroom, where you want to have a more subdued atmosphere when you bring in your date for the first time. That is why I have on the nightstands incandescent lights with dimmers. 

But, yes, we are probably conditioned by our past of incandescent lights and CFLs just replicated that.

[Simon]

Well I landed up with a couple of 2700K 3W bulbs. Whilst i used my bedroom as a study I had a 10W 5500K but recently swapped it with the 3W on the landing so that I could leave it on over chrismas and have some light show in every room to deter breakins. I have not actually bothered to take the 3W 2700K light out of my bedroom yet as the only thing I do there now is sleep I figured I did not need the 10W 5500K bulb. But given my aversion to warmer light as my colour perception is off I must have "daylight" anywhere else and i never have a problem going to sleep even in front of a computer screen that experts recommend we not use for a couple of hours before going to bed.

[Nusa]

Apples and pears are much more closely related than apples and oranges. They all grow on trees, but apples and pears both require a cold weather cycle to produce, while citrus trees only do well in warm climates.

[Simon]

To not be comparing apples to apples is something I hear more often

[coppice]

To not be comparing apples to apples is something I hear more often

Yeah, I know, but I could care less. 

Lots of people hear expressions, don't get the idea, and oddly misstate them.

[Ducttape]

This is pretty trivial, but I just thought I'd mention that if you're very far into 'warm' room lighting, then the band colors of a resistor in hand won't match the colors of the bands in a resistor band chart on your monitor. Of course it'd still match a printed out resistor band chart.

[Simon]

To not be comparing apples to apples is something I hear more often

Yeah, I know, but I could care less. 

Lots of people hear expressions, don't get the idea, and oddly misstate them.

There are no rules about these sayings, they change over time based on what the majority prefer to say.

[Red Squirrel]

We need a more EE version of the saying.

Let's not go comparing scopes with multimeters here.     

[TERRA Operative]

According to the white balance setting on my cameras with the white balance card, my bench lighting is about 4100K.
I made sure to use high CRI led strips too, as accurate colour rendition is arguably more important than colour temperature IMO.

Bright, wide-spectrum light means less eye strain in the long run I've found. The absolute colour temperature isn't as important beyond personal preference (within reasonable values).

[Kjelt]

I made sure to use high CRI led strips too, as accurate colour rendition is arguably more important than colour temperature IMO.

Yes if you are in the fashion , graphical industry or make YT vids.
Otherwise meah. As long as they are real white leds with phosphor not the RGB leds those are horrrible an abonimation for the term white led (and I am not being racist here for the PC crowd).
You're brains compensate perfectly what you were expecting to see.
Try a red can of cocacola and put it in 2200-2700K light, wait two minutes and keep looking.
Now put it in 6000K light and again keep looking for two minutes.
Interesting he?

[Red Squirrel]

Are T8 bulbs considered to have good CRI?  Or is that strictly a LED thing?   Thinking of putting some fixtures in my computer room.  2 dual bulb fixtures should do the trick.  I have a lamp stand with a single LED bulb now but not quite as bright as I'd like it.  I do plan to do some YT stuff in there as well.

[nctnico]

Are T8 bulbs considered to have good CRI?  Or is that strictly a LED thing?   Thinking of putting some fixtures in my computer room.  2 dual bulb fixtures should do the trick.  I have a lamp stand with a single LED bulb now but not quite as bright as I'd like it.  I do plan to do some YT stuff in there as well.

There is no generic rule on CRI. You have to check the datasheet of the bulb for the actual number.

[rdl]

Yeah, incandescent and halogen almost always have very good CRI, but you can find fluorescent and LED with either bad or good CRI. It depends on how they are made. You have to check the specifications for which ever ones you are interested in.

[MrMobodies]

I like the 11w fluorescent daylight bulbs and I got a couple of them.

They seem to make the room like nice in the dark.

[Kjelt]

Are T8 bulbs considered to have good CRI?  Or is that strictly a LED thing? 

Depends on the series.
For instance the Philips 9a0 series have very good cri where a = colourtemperature.
So 940 is 4000K , 930 is 3000K
The 8a0 series has less good CRI.

[raptor1956]

I'm looking to change some of my lighting to lower temp bulbs in hopes that might improve my sleep, which is not very good.  If this is the goal then is 2700K to be preferred to 3000K or is the difference not so significant.  I currently have many LED bulbs for lighting and my workbench has LED strip lighting and all of them are 5000K or higher so the blue light might be playing a role in my sleep problems.

If sleep is an issue what factors play a role?  Assuming you have some lighting that's say, 5000K+ and other lighting at, say 2700K -- how long before bed should the cooler lights be turned off?  A similar problem is related to PC usage as most modern monitors are LED backlit and the color temp tends to be above 5000K -- how long before bed should you shut the PC down to limit blue light problems?  Is there an app or widget that you can use to toggle between two monitor color settings so that near bedtime you can switch to a warmer color?

What are some good brands of 60W and 100W equivalent LED's in the 2700K range that can be purchased on Amazon?


Brian

[Kjelt]

Lower colour temperature is preferable before sleep. I have two hue bulbs in a fixture in my bedroom and half hour before sleep I put them on very yellowish light and dimmed to low lumens, 15 minutes before sleep I put them on another preference setting making it orange and even lower lumens.
I kind of imitate the sun going down and get sleepier.
Ofcourse you can not read a book anymore and phone ir pad usage is not preferred although they nowadays also have a night setting with lower colourtemperature.

TV or PC is very cold white for good colourrendering, I thought about 6500K, and should be avoided at least an hour before bedtime, it will just upset your biological rhythm.

I am no expert but there must be tens if scientific articles about it.
Google "sleeping and color temperature" and "light and biorythm" that sort of keywords should result in many hits.

Each person is unique so you might want to experiment, write down your light and times before sleeping and next morning how you slept. Find your own optimal lighting formula. Some people are night owls some are early raisers.

The biggest win I myself have gained is with waking up with light with the lightalarmclock. Since I have that my wintermood when awakening is gone. I was always grumpy and miserable when my alarmclock went off in the cold and dark wintermornings. This lightalarm starts with very low red light 20 minutes before time to wake up and goes to bright warm white light when it is time. Works for me.

[apis]

My understanding is that it depends on the wavelength of the light, not the white light color temperature.
The cells that regulate the biological rhythm are more sensitive to blue light, so if you have lots of blue light the body thinks it's the middle of the day. On a screen you can turn down the blue component which makes everything look warmer. But if you only make a white light warmer by adding red color you still have the same amount of blue.

For indoor lighting during the day it should be better to have more blue light in the mix, and in the evening you would want less blue to help the body adjust its rhythm.

This is just my impression, I might be wrong.

[Edison]

I have a so-called biological alarm clock, it's shaped like a ball, and it's not just a shape that mimics the sun.
Can mimic the sun light, when I go to sleep, I can light it like a lamp - it gradually changes the color of light and the brightness from white to dark red (sunset), in the morning it goes from the red to the white and it can make the sounds of the awakening of nature (sunrise) - this takes about 30 minutes .

[SeanB]

Lower colour temperature is preferable before sleep. I have two hue bulbs in a fixture in my bedroom and half hour before sleep I put them on very yellowish light and dimmed to low lumens, 15 minutes before sleep I put them on another preference setting making it orange and even lower lumens.
I kind of imitate the sun going down and get sleepier.
Ofcourse you can not read a book anymore and phone ir pad usage is not preferred although they nowadays also have a night setting with lower colourtemperature.

TV or PC is very cold white for good colourrendering, I thought about 6500K, and should be avoided at least an hour before bedtime, it will just upset your biological rhythm.

I am no expert but there must be tens if scientific articles about it.
Google "sleeping and color temperature" and "light and biorythm" that sort of keywords should result in many hits.

Each person is unique so you might want to experiment, write down your light and times before sleeping and next morning how you slept. Find your own optimal lighting formula. Some people are night owls some are early raisers.

The biggest win I myself have gained is with waking up with light with the lightalarmclock. Since I have that my wintermood when awakening is gone. I was always grumpy and miserable when my alarmclock went off in the cold and dark wintermornings. This lightalarm starts with very low red light 20 minutes before time to wake up and goes to bright warm white light when it is time. Works for me.

Did that as well, took a cheap LED clock radio, and voided the warranty on it, after checking the clock itself worked. Cut the main board in half to leave the clock side mostly there ( there was a bit of the radio board components left, but they were effectively disconnected) so there was room to fit in a hockey puck sized opto relay block, and wired it up to give a switched mains output, leading outside the case to a US in line socket. Standard bedside light then plugged into it, and for light I use a somewhat old ( as in pre war) 16 candlepower Siemens carbon filament lamp in the lamp itself. Wake up to a warm light that comes on a half hour before sunrise in winter, but in summer it is disconnected and put away, as the sun rises at 5AM then and I will wake with it through the curtains. Do not need the extra heat added to the current summer indoor of 29C and 60% RH.

[Kjelt]

My understanding is that it depends on the wavelength of the light, not the white light color temperature.
The cells that regulate the biological rhythm are more sensitive to blue light, so if you have lots of blue light the body thinks it's the middle of the day.
This is just my impression, I might be wrong.

No you are for the big part correct, they have discovered sensors in the eye that are very sensible for the wavelenghth of blue light which regulate your biorythm.
The part you might miss is that white light expressed in colourtemperature follows the black mass radiator curve (see wiki in previous post) and that lower colour temperatures have less to none bluish light in their spectrum while higher colourtemperatures have more to much bluish energy in their spectrum.
So the black mass body radiator curve follows the sun, from rise (little blue) to noon ( much blue) to set ( little blue again).
Probably evolution has done the rest.

[apis]

The part you might miss is that white light expressed in colourtemperature follows the black mass radiator curve (see wiki in previous post) and that lower colour temperatures have less to none bluish light in their spectrum while higher colourtemperatures have more to much bluish energy in their spectrum.

That is only true for black body radiators, like the sun, halogen or tungsten lights. LEDs and fluorescents don't have a nice black body spectrum. That is why they have less good color rendering index than tungsten. To get light that looks white all you need is a red green and a blue led, and then you can vary the intensity of each component make it look like any colour temperature you want. That is how computer monitors work (as I'm sure you know).

Say we're working at a lamp factory that are making lamps with adjustable color temperature. One way of doing it (I'm not saying this is how they do it, but it's a possibility) would be to have cold white LEDs + an orange LED. Then to turn down the color temperature you simply increase the amount of orange light while the blue component remains the same. Now that I'm thinking about it, it would probably make more sense to do it the other way around: have a warm white light and add some blue to make it look like higher temperature, but who knows.

If you try to simulate twilight by just adding red light then it won't work, since they eyes still get the same amount of blue.

[Kjelt]

To get light that looks white all you need is a red green and a blue led, and then you can vary the intensity of each component make it look like any colour temperature you want. That is how computer monitors work (as I'm sure you know).

no i thought they only had fluotubrs or white leds backlght and they "fake" the colortemperature by the lcd panels offset.

[apis]

To get light that looks white all you need is a red green and a blue led, and then you can vary the intensity of each component make it look like any colour temperature you want. That is how computer monitors work (as I'm sure you know).

no i thought they only had fluotubrs or white leds backlght and they "fake" the colortemperature by the lcd panels offset.

That's right. The lcd filters the light from the lcd backlight through a red, bule and green filter. So you can lower the color temperature by letting through less blue light... But it depends on the display technology. (The point was only that you don't need a black body spectrum to generate white light.)

Actually that makes me wonder what kind of LEDs they use as backlight in LCDs, it would be more energy efficient to create the backlight using a combination of red blue and green LEDs. But since they previously used phosphorus based backlights it might be easier to just use phosphor coated blue LEDs.

[Kjelt]

It would be very difficult for flat panels to get a good to perfect colourmixing of rgb leds for it to become uniform white.

[steve30]

Are T8 bulbs considered to have good CRI?  Or is that strictly a LED thing?   Thinking of putting some fixtures in my computer room.  2 dual bulb fixtures should do the trick.  I have a lamp stand with a single LED bulb now but not quite as bright as I'd like it.  I do plan to do some YT stuff in there as well.

The modern bog-standard tubes have a CRI of >80 and are pretty good, but not as good as the more expensive tubes that have a CRI of >90.

Tubes with a >90 CRI are available from Osram and Philips. I have them in both T8 and PLL form factors. Pretty sure you can get them in T5 as well.

If you go to proper lighting supplier you should be able to select an exact product and the specification will be listed with CRI, colour temp etc (as opposed to a hardware store where the only options will be something vague like 'T8 Tube').

[coppice]

Are T8 bulbs considered to have good CRI?  Or is that strictly a LED thing?   Thinking of putting some fixtures in my computer room.  2 dual bulb fixtures should do the trick.  I have a lamp stand with a single LED bulb now but not quite as bright as I'd like it.  I do plan to do some YT stuff in there as well.

The modern bog-standard tubes have a CRI of >80 and are pretty good, but not as good as the more expensive tubes that have a CRI of >90.

Tubes with a >90 CRI are available from Osram and Philips. I have them in both T8 and PLL form factors. Pretty sure you can get them in T5 as well.

If you go to proper lighting supplier you should be able to select an exact product and the specification will be listed with CRI, colour temp etc (as opposed to a hardware store where the only options will be something vague like 'T8 Tube').

Two lamps which claim a CRI of 90 can be very different in their illumination properties, so don't be too trusting of CRI scores. CRI is very gameable, which is why the industry is trying to move away from it, and use TM-30 instead. Both white LEDs and fluorescent tubes use phosphors to generate white light, so they are subject to similar limitations when trying to achieve a high CRI or TM-30 score. Phophors do not give black body type spectra. A mixture of phosphors is used to fudge an approximation to a black body spectrum. However, even the best fudging results in quite a spiky spectrum. How the peaks and troughs of that spiky spectrum align with peaks and troughs in the reflection pattern of an object can significantly affect its perceived colour.

[macboy]

Are T8 bulbs considered to have good CRI?  Or is that strictly a LED thing?   Thinking of putting some fixtures in my computer room.  2 dual bulb fixtures should do the trick.  I have a lamp stand with a single LED bulb now but not quite as bright as I'd like it.  I do plan to do some YT stuff in there as well.

The modern bog-standard tubes have a CRI of >80 and are pretty good, but not as good as the more expensive tubes that have a CRI of >90.

Tubes with a >90 CRI are available from Osram and Philips. I have them in both T8 and PLL form factors. Pretty sure you can get them in T5 as well.

If you go to proper lighting supplier you should be able to select an exact product and the specification will be listed with CRI, colour temp etc (as opposed to a hardware store where the only options will be something vague like 'T8 Tube').

Two lamps which claim a CRI of 90 can be very different in their illumination properties, so don't be too trusting of CRI scores. CRI is very gameable, which is why the industry is trying to move away from it, and use TM-30 instead. Both white LEDs and fluorescent tubes use phosphors to generate white light, so they are subject to similar limitations when trying to achieve a high CRI or TM-30 score. Phophors do not give black body type spectra. A mixture of phosphors is used to fudge an approximation to a black body spectrum. However, even the best fudging results in quite a spiky spectrum. How the peaks and troughs of that spiky spectrum align with peaks and troughs in the reflection pattern of an object can significantly affect its perceived colour.

This is good, accurate information.

However, given no other concrete data I would absolutely buy an LED bulb with a 90 CRI rating over a 80 CRI or an unspecified one. About a year ago I bought a few "90+" CRI LEDs and I was quite impressed with the color rendition and just general look/perception of the light. In fact I was so impressed that I went back and bought many more and replaced nearly all the other working LED bulbs (and a few CFLs) around my house with these new ones. I was lucky that they came in many form factors, including normal E26 frosted bulbs, flood lights, and candelabras, as well as GU10 floods. I used them all.

I recently acquired a Spectrophotometer (thanks, Santa/DW), so I thought I'd take a few measurements. My favored "90+ CRI" bulbs measure at 91.6 CRI according to my device (and ArgyllCMS software). Every other LED around the house measured less than 81 CRI. The most pleasant white temperature to my eye is 3000K, but I'll qualify that: that is at night (no sunlight mixing), and it happens to be the white temperature of the nice 90+ CRI bulbs. Some other bulbs with 2700K or 3300K also have a poorer CRI so that may bias my opinion. For reference, a small 20 W halogen desk lamp measures 99.2 CRI, with a white temperature between 3000 and 3300K (I forget exactly, but I'll update this post with the number). That halogen lamp sits next to my color printer in the office. Guess why! If anyone is interested I can post the actual spectra of the various LEDs.