can an energy saving bulb be run off DC ?

[Simon]

As above. Could i run a standard energy saving bulb on 240V DC ? I'm guessing they use switch mode voltage converters in them so must be DC/DC so they must rectify the mains at the input ?

[mikeselectricstuff]

Probably, but remember that 240VAC rectified does not make 240VDC - it's around 330V.
YMMV with different makes, but all the ones I've seen rectify the mains and so should work on DC.
Note however that any internal fuse may suffer arcing problems at DC in the case of an internal fault.

[Zero999]

Yes, a CFL will work off DC.

I'm not sure if it'll work at full brightness on 240VDC. After the rectifier, there's a smoothing capacitor with just below the peak mains voltage on so you may need 325V to get full brightness.


Plenty of information can be found on CFL circuits in the Internet:
http://www.nxp.com/documents/application_note/AN00048.pdf
http://www.pavouk.org/hw/lamp/en_index.html
http://www.google.co.uk/search?client=opera&rls=en&q=CFL+circuit&sourceid=opera&ie=utf-8&oe=utf-8&channel=suggest

[Ed.Kloonk]

 

[johnwa]

As others have said, it is possible to run CFLs from DC. However, be aware that there are a few different designs of the driver circuits for them. The older ones used a bridge rectifer straight into a filter cap on the input. These will work fine on 340VDC. However, the power factor of this design is pretty terrible, so in recent years a new design has been showing up. These isolate the filter cap from the rectifer with another diode, and the tube is run from the unfiltered DC - the filter cap only supplies the control circuit. Since the tube supply in this design is only 240VRMS, the tube will be overdriven  if run from 340VDC.

I once built an inverter for driving these that supplied 340VDC, pulse width modulated to provide an appropriate RMS value. It may be possible to find a suitable DC value between 240V and 340V that provides acceptable operation. (The driver circuit is underdriven at 240VDC, and the transistors may not saturate). It would probably be best to measure the power consumption, and get it to equal the value when the bulb is driven from 240VAC.

[Zero999]

As others have said, it is possible to run CFLs from DC. However, be aware that there are a few different designs of the driver circuits for them. The older ones used a bridge rectifer straight into a filter cap on the input. These will work fine on 340VDC. However, the power factor of this design is pretty terrible, so in recent years a new design has been showing up.

I've never seen a power factor corrected CFL before. There are no requirements for it in the EU as a CFL draws under 100VA. I don't know about other jurisdictions.

These isolate the filter cap from the rectifer with another diode, and the tube is run from the unfiltered DC - the filter cap only supplies the control circuit. Since the tube supply in this design is only 240VRMS, the tube will be overdriven  if run from 340VDC.

I don't see how powering a power factor corrected CFL from 340VDC would cause any damage. It might not like it but I doubt it would go bang.

An active power factor correction unit is typically a boost converter before the DC reservoir capacitor which outputs an equal or slightly higher DC voltage than the mains peak voltage. In the more complex designs, the PWM of the switching transistor is sometimes varied to ensure the current drawn is perfectly sinusoidal. The simplest active power correction units don't vary the PWM, it's just a boost converter with a very long time constant in the feedback network so the PWM remains roughly constant (longer than a couple of AC cycles) but the current varies in phase with the AC and is not perfectly sinusoidal but better than the classic rectifier+filter capacitor design.

My guess is that if a CFL had PFC, it would use the latter of the techniques described above so powering directly from DC shouldn't be a problem.

[johnwa]

I've never seen a power factor corrected CFL before. There are no requirements for it in the EU as a CFL draws under 100VA. I don't know about other jurisdictions.

OK, perhaps these are not as common as I thought. There are a few CFL schematics at http://www.pavouk.org/hw/lamp/en_index.html, but the only one with the PFC circuit is actually an electronic ballast for a linear tube.

I don't see how powering a power factor corrected CFL from 340VDC would cause any damage. It might not like it but I doubt it would go bang.

An active power factor correction unit is typically a boost converter before the DC reservoir capacitor which outputs an equal or slightly higher DC voltage than the mains peak voltage. In the more complex designs, the PWM of the switching transistor is sometimes varied to ensure the current drawn is perfectly sinusoidal. The simplest active power correction units don't vary the PWM, it's just a boost converter with a very long time constant in the feedback network so the PWM remains roughly constant (longer than a couple of AC cycles) but the current varies in phase with the AC and is not perfectly sinusoidal but better than the classic rectifier+filter capacitor design.

My guess is that if a CFL had PFC, it would use the latter of the techniques described above so powering directly from DC shouldn't be a problem.

The circuit is not very sophisticated, it just draws some of the operating power from the unfiltered source, so that the load is spread over the full mains cycle, rather than being in one lump at the voltage peak. I think the problem is that this type of circuit responds more to the RMS value of the input than the peak, so substituting an input waveform with a different RMS to peak ratio (1 for DC, 1/sqrt(2) for AC sine) could be an issue.

But it looks like most CFLs still use the standard rectifier + filter circuit, so they should be fine on 340VDC. It might still be a good idea to check that the current consumption is not significantly above that calculated from their power rating, to ensure long life.

It is also possible to run other 240VAC input SMPSs from 340VDC - this can provide benefits in efficiency and reduced complexity if you are building an inverter. The only possible problems would be the breaking capacity of the fuses and switches.

[scrat]

Why not trying to measure the voltage on the CFL when supplied with the mains, and then starting with a low DC value, and increasing unless it reaches the same output?

[Leo Bodnar]

Move on to LED lamps.  They have better power efficiency and smoother spectrum.
They are now cheap enough to beat CFLs unless you buy them from B&Q.

[Zero999]

The circuit is not very sophisticated, it just draws some of the operating power from the unfiltered source, so that the load is spread over the full mains cycle, rather than being in one lump at the voltage peak. I think the problem is that this type of circuit responds more to the RMS value of the input than the peak, so substituting an input waveform with a different RMS to peak ratio (1 for DC, 1/sqrt(2) for AC sine) could be an issue.

So you mean they just omit the filter capacitor? That would make the power factor better at the expense of flicker so it looks like a lamp powered from a traditional iron ballast.

Move on to LED lamps.  They have better power efficiency

I doubt that, in fact most LED lamps have poorer efficiency than a CFl.
http://en.wikipedia.org/wiki/Luminous_efficiency#Examples_2

LEDs tend to be better for direct light sources though such as replacing a halogen.

[NiHaoMike]

Modern LEDs are easily more efficient than fluorescent. That's one of the reasons why newer LCD backlights are LED. In addition, LEDs are physically tougher than fluorescents, can be dimmed practically to zero, and can be switched frequently without any impact on lifetime.

[Zero999]

Modern LEDs are easily more efficient than fluorescent. That's one of the reasons why newer LCD backlights are LED.

Old LCDs used cold cathode fluorescent lamps which were worse than compact fluorescents.

A naked Cree LED is better than a CFL but it's not cheap and the efficiency doesn't account for the losses in the power supply or the luminaire.

The best LED light listed on Wikipedia is    5.4 W LED screw base lamp (100 V 50/60Hz)   14.9%

The best fluorescent listed on Wikipedia is a T5 tube powerd by an electronic ballast   15.63%

Of course I know this is Wikipedia here but it does show that generally LEDs with integrated ballasts and packaging are at best around equal to CFLs but are often worse.

[Leo Bodnar]

Have a look at CFL spectrum. It is horrible.

[Zero999]

A white LED's is hardly perfect either, a large blue peak makes blue brighter than other colours.

[Leo Bodnar]

A white LED's is hardly perfect either, a large blue peak makes blue brighter than other colours.

This must be old cold white LED.  Things have moved on since then.

Yes, LEDs do not have emission spectrum of perfect black body (sic), D65 source or even the Sun but at least they do not have a few strong emission lines with huge areas in between with no light at all like CFLs. If two coloured objects happen to have colour difference in empty areas between CFL spikes their colours will look exactly the same to the eye (or any other receiver for that matter.)
Try sorting your black socks under CFL lamp - they will most probably will be wrongly paired in the morning.
This is called metamerism.

Same problem exists for "white" light generated by set of RGB LED triplets - they have three narrow spectral emission lines and nothing in between.
It looks white when you shine it on a white or grey object but as soon as you start looking at objects with complex reflection spectra the things start to look "weird."

Here are few spectra I have taken around the house: a new T8 CFL tube, cheapo Chinese GU10 LED lamps and Philips LED bulb.

[Simon]

thanks for all the replies guys, for some reason I got no notification (and not the first time - I think thee are issues, will have to have a word with dave)

Basically the source of the question is the fact that I have my nice solar panels and plans to add more, but with my recent GTI experiment I'm not sure i'm going down that road again.

So I thought, why not just charge my battery(s) and then when i get home use the power to run the lights (I have separate circuits for upstairs and downstairs so can minimize the load initially). I could build some sort of inverter that produces mains voltage DC and screw all those crap inverters on the market. Yes LED does sound attractive but that means that I'd have to use a SMPS to drop the mains voltage when I'm out of battery so not sure about efficiency.

Yes CFL spectrum's are crap, i started a thread about this a while ago as I've tried a number of bulbs ranging from 2700K (the normal shit in the shop that is just yellow) right up to 5500K which ends up looking too blue. With the narrow spectrum a good compromise despite daylight being 5500K is 3500K. What also makes 5500K look bad is having other 2700K's nearby and your used to those so you get duped. (the brain actually does auto white balance correcting, once upon a time in photography you had to use a different film for each light source when you could not visually tell the difference)

[Zero999]

Here are few spectra I have taken around the house: a new T8 CFL tube, cheapo Chinese GU10 LED lamps and Philips LED bulb.

But aren't warm white LEDs less efficient since more phosphor is applied to the die there will be more loss in converting the blue to longer wavelengths.

The spectrum of CFLs varies widely, some are better than others, same for LEDs.
http://ioannis.virtualcomposer2000.com/spectroscope/toyspectroscope.html

Buy and expensive, good quality LED light and it'll be more efficient than any CFL, get a cheap Chinese LED light and it'll be much worse, I've seen some of the crappy lights in my local store.

[Leo Bodnar]

But aren't warm white LEDs less efficient since more phosphor is applied to the die there will be more loss in converting the blue to longer wavelengths.
The spectrum of CFLs varies widely, some are better than others, same for LEDs.

There is efficiency and there is efficiency.  There is also efficacy which is efficiency projected onto human eye sensitivity.
You can have very efficient monochromatic light (like laser) but who would want to use it as home lighting?

We probably need to agree what we are discussing here. I think "efficiency" should include nice (preferably continuous) spectrum, brightness per volume, price, lifespan and dangerous materials (e.g. CFLs contain mercury.)

Sure, there are some expensive CFLs for use in colour matching in printing industry and for photo studio lighting.
I just measured what I have around an average home (stuff you buy from eBay and B&Q.)

[Zero999]

CFLs contain virtually no mercury. The greatest hazards are the glass tube and the phosphor which is often poisonous and lead solder.

LEDs have the advantage of being not being made of glass.

My point I suppose is don't just go on the press releases by Cree on efficiency, look at the real life lamps.

[Leo Bodnar]

My point I suppose is don't just go on the press releases by Cree on efficiency, look at the real life lamps.

So how one to measure efficiency of "real life lamps?"

CFLs contain virtually no mercury.

How do you know?  I hope you did not pick up this knowledge from wikipedo. What element creates the spectrum peak at 546nm then?

[Zero999]

My point I suppose is don't just go on the press releases by Cree on efficiency, look at the real life lamps.

So how one to measure efficiency of "real life lamps?"

As you probably know it's subjective.

I think we both agree it's a balance between spectrum, price and brightness vs power consumption. I just think that LEDs aren't quite there yet, unless you're willing to buy good Cree LEDs. In my experience, CFLs are always dimmer than the incandescent they're supposed to be equivalent to and LEDs seem to be even worse.

How do you know?  I hope you did not pick up this knowledge from wikipedo. What element creates the spectrum peak at 546nm then?

Multiple sources reveal the amount of mercury in a CFL is something like 5mg which is almost nothing unless you keep breaking them, the phosphor and broken glass are much more dangerous.
http://www.treehugger.com/files/2007/05/ask_treehugger_14.php

[Simon]

I think we both agree it's a balance between spectrum, price and brightness vs power consumption. I just think that LEDs aren't quite there yet, unless you're willing to buy good Cree LEDs. In my experience, CFLs are always dimmer than the incandescent they're supposed to be equivalent to and LEDs seem to be even worse.

The reason why CFL's are not as good as it says "on the tin" is because of what i keep telling people who mostly don't listen or understand: colour temperature. They emit yellow light, that is not the same as the same power of white light. But then if your using a meter sensitive to yellow light you can claim certain power ratings. As i keep saying 2700K CFL's are a con and should be banned !

Multiple sources reveal the amount of mercury in a CFL is something like 5mg which is almost nothing unless you keep breaking them, the phosphor and broken glass are much more dangerous.
http://www.treehugger.com/files/2007/05/ask_treehugger_14.php

5 mg of mercury is 5 mg of mercury. Mercury is very hazardeous. From memory 1g of mercury pollutes thousands (10'000 ?) of litres of water

[Leo Bodnar]

The reason why CFL's are not as good as it says "on the tin" is because of what i keep telling people who mostly don't listen or understand: colour temperature.

The term "colour temperature" cannot be applied to highly spiky spectrum like that of CFLs or e.g. an RGB LED. It just makes no sense.

[Simon]

you can define the colour temperature of a CFL. I'm sure if you were to measure the colour it would come back with a colour. Of course that might not be the colour of the main colour spike but will be what we see it as based on all the colours emitted. If it looks yellow (2700K) that's what it is.

[Zero999]

Simon, I don't know if I agree. I recall the horrible high colour temperature blue CFL being dimmer than the warm white lamp round your house, despite being the same power rating.

Come to think of it, I've seen some good LED lamps at the swimming pool at Calvert but they probably weren't cheap and I don't know what the power rating was. All the changing rooms were lighted by LEDs, it was just the poolside which had flat panel fluorescent lamps.

I think, if you want to go for LEDs then fork out for some Cree LEDs and run the whole house lighting off DC. Use a decent SMPS for when there isn't enough energy in the batteries. Li-ion batteries are more efficient than lead acid, but they're expensive, have a limited life, need careful charging and should be kept in an outbuilding a safe distance away from your house.