Author Topic: Getting UV light from a blackbody radiator?  (Read 3074 times)

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Offline CatalinaWOW

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Re: Getting UV light from a blackbody radiator?
« Reply #25 on: January 14, 2019, 04:18:59 am »
By the way, the blues and purples in the operating picture shows that these are at least trying harder than the ones measured by JimDeane. 
 

Offline helius

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Re: Getting UV light from a blackbody radiator?
« Reply #26 on: January 14, 2019, 04:44:30 am »
You have a (qualitative and unreplaceable) spectrophotometer for UV-A in your Mark I eyeballs—exposure to even indirect UV of much intensity (as to cause fluorescence on optically brightened paper and cloth) by the unprotected eyes will cause dryness and irritation from damage to the conjunctiva.
This is one reason I am not a fan of blacklight paintings/posters or unshielded UV lamps in public spaces.
 

Offline raptor1956

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Re: Getting UV light from a blackbody radiator?
« Reply #27 on: January 14, 2019, 05:52:13 am »
An interesting thing about incandescent bulbs is that with higher voltage you get higher temps and bluer light but at the expense of lifespan.  Voltage is REAL important here as lifespan is related to voltage to the fourth power so even a small change in voltage can make a huge difference in lifespan.  OTH, if you ran the bulb below rated voltage it could last a very long time at the expense of light output and color.  LED bulbs are way more efficient but the quality of light is not so good.  There have been improvements, but getting really high CRI isn't easy or cheap.  LED bulbs are now getting fairly cheap if you buy in bulk -- I just bought a 16-pack of 60W 2700K Phiips LED's from Amazon for less than $2/each.  What would be nice is a practical LED bulb that you can adjust the color temp from warm (2700K) to about 4000K or even 5000K -- I could see a multi-LED bulb with RGB LED's to accommodate that by varying the ratio of power to each.  Probably still need some phosphors an filter coatings to flatten the spectrum.


Brian
 

Offline helius

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Re: Getting UV light from a blackbody radiator?
« Reply #28 on: January 14, 2019, 07:18:38 am »
I'm struggling to see what your post has to do with UV radiation?
Anyway, the lamps that can change their color temperature are the Philips "Hue" and equivalents from other brands. They are not cheap, costing at least $30 each for color adjustability.
 

Offline Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #29 on: January 14, 2019, 09:08:04 am »
I think he meant: more volts = more UV.

You have a (qualitative and unreplaceable) spectrophotometer for UV-A in your Mark I eyeballs—exposure to even indirect UV of much intensity (as to cause fluorescence on optically brightened paper and cloth) by the unprotected eyes will cause dryness and irritation from damage to the conjunctiva.
This is one reason I am not a fan of blacklight paintings/posters or unshielded UV lamps in public spaces.
UVA blacklights are fairly benign. You get more exposure on a sunny day. I remember trying to give myself a tan with a couple of 8W blacklight blue tubes, when I was a teenager. I put the tubes in a PCB exposure unit and pressed my face against the glass for around five minutes, didn't even close my eyes and didn't suffer any eye problems. Of course I don't recommend this and it was a stupid thing to do.
 

Offline Nerull

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Re: Getting UV light from a blackbody radiator?
« Reply #30 on: January 14, 2019, 09:33:56 am »
I actually took a spectrum from a "Black Light Bulb" purchased at Wal-Mart in the US during the halloween season. I wanted to compare it to LED and fluorescent versions. Turns out...not black light at all. Not even trying.

I thought I recalled black light incandescent bulbs actually working (causing fluorescence in fabrics, dyes) back in the 1980s. Now this one at least is a huge fake.

I'm attaching the spectrum.

A lot of materials don't need UV to fluoresce. My green laser pointer causes quite a bit of florescence, I would imagine that blue or violet causes even more.

If you go outside during the day and look up there's a pretty good example of a blackbody radiator emitting fairly significant amounts of UV up in the sky.
« Last Edit: January 14, 2019, 09:37:03 am by Nerull »
 

Offline jimdeane

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Re: Getting UV light from a blackbody radiator?
« Reply #31 on: January 14, 2019, 06:50:39 pm »
I actually restricted it (in another test) to just wavelengths below 500 nm. It was flatline.
 

Offline jimdeane

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Re: Getting UV light from a blackbody radiator?
« Reply #32 on: January 14, 2019, 06:52:50 pm »

I haven't looked at trying a log axis on this particular piece of software. UV would be visible as a curve if it existed coming from this bulb, which it doesn't. That's all I cared to find out.
 

Offline jimdeane

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Re: Getting UV light from a blackbody radiator?
« Reply #33 on: January 15, 2019, 03:52:49 pm »
Here's a photo of the "fake black light".  It did not make anything fluoresce at all, but it was very hot. To the Mk1 eyeball it did not look as "bright" as this, the camera picked up lots of infrared. It looked deep, deep red, but I think there is a bluish pigment on the bulb so when you look at it it may look purple-ish.

My speculation:  wood's glass is expensive, they quit using it and went to some generic "dark glass" that unfortunately only lets through deep red. Or someone mixed up "black light" and "heat lamp" at the factory in China.
 
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Offline Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #34 on: January 15, 2019, 04:42:28 pm »
Here's a photo of the "fake black light".  It did not make anything fluoresce at all, but it was very hot. To the Mk1 eyeball it did not look as "bright" as this, the camera picked up lots of infrared. It looked deep, deep red, but I think there is a bluish pigment on the bulb so when you look at it it may look purple-ish.

My speculation:  wood's glass is expensive, they quit using it and went to some generic "dark glass" that unfortunately only lets through deep red. Or someone mixed up "black light" and "heat lamp" at the factory in China.
It's probably an infrared lamp designed for use with security camera, rather than a black light. In which case the spectrum certainly makes sense.
 

Offline CatalinaWOW

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Re: Getting UV light from a blackbody radiator?
« Reply #35 on: January 15, 2019, 05:38:08 pm »
JimDeane's "fake" looks identical to the two brands I have.  I can't guess at motivation, but clearly it wasn't accident.
 

Offline apis

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Re: Getting UV light from a blackbody radiator?
« Reply #36 on: January 15, 2019, 08:11:44 pm »
Is it possible it's a 230 V lamp?
 

Offline CatalinaWOW

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Re: Getting UV light from a blackbody radiator?
« Reply #37 on: January 15, 2019, 09:20:34 pm »
At least one of mine is clearly marked 120 volts.  Given how hot they run on 120 V, I can hardly imagine how hot they would get fed 220 V
 

Offline Beamin

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Re: Getting UV light from a blackbody radiator?
« Reply #38 on: March 02, 2019, 12:51:47 am »
Here's a photo of the "fake black light".  It did not make anything fluoresce at all, but it was very hot. To the Mk1 eyeball it did not look as "bright" as this, the camera picked up lots of infrared. It looked deep, deep red, but I think there is a bluish pigment on the bulb so when you look at it it may look purple-ish.

My speculation:  wood's glass is expensive, they quit using it and went to some generic "dark glass" that unfortunately only lets through deep red. Or someone mixed up "black light" and "heat lamp" at the factory in China.

That doesn't look right. I think the real ones are woods glass with an insanely bright and short life filament inside. Those get dangerously, I remember combing my hair and spec of water touched the bulb and it exploded shooting insanely hot glass that melted the carpet. It did make black light posters glow.  I wonder what % is actually UVA. Normal light bulbs are only 1 or 5% light vs IR, the brighter or whiter/bluer the lower that % goes. Is a Low pressure sodium still the most light per watt (ignoring CRI) or have LEDs surpassed this efficiency mark? Problem with LPS is they making things look black and white or orange and white even worse then the high pressure sodium which has almost no color besides that orange peak.

Would it be possible to make a true black and white light? Have a light that puts out real sharp spectrums that trick the rods in your eyes. Be a pretty cool effect but only 1 color/black maybe physically possible.


How do the green laser pointers make fluorescent paper, except green and blue, fluoresce? The ones that take IR and half it to 532nm work really well as black lights.
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Offline GeoffreyF

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Re: Getting UV light from a blackbody radiator?
« Reply #39 on: March 02, 2019, 07:52:42 pm »
I don't think you understand what is meant by "Black Body Radiation" or "Black Light".  It appears to me you are riffing on "Black" and "Radiation" without understanding either phrase.

Rather curious what books or wiki you have read on these subjects.  Probably none, but if some, still curious.
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Offline IanMacdonald

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Re: Getting UV light from a blackbody radiator?
« Reply #40 on: March 02, 2019, 08:40:19 pm »
Regular halogen capsule bulbs give off some UV, in fact it's not recommended to use them where people can look into them, without a UV filter.  8)
 

Offline tooki

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Re: Getting UV light from a blackbody radiator?
« Reply #41 on: March 03, 2019, 12:29:10 am »
That doesn't look right. I think the real ones are woods glass with an insanely bright and short life filament inside. Those get dangerously, I remember combing my hair and spec of water touched the bulb and it exploded shooting insanely hot glass that melted the carpet. It did make black light posters glow.  I wonder what % is actually UVA. Normal light bulbs are only 1 or 5% light vs IR, the brighter or whiter/bluer the lower that % goes.
I already provided that number in the second reply to this entire thread.
 

Offline Beamin

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Re: Getting UV light from a blackbody radiator?
« Reply #42 on: March 09, 2019, 09:17:08 pm »
I don't think you understand what is meant by "Black Body Radiation" or "Black Light".  It appears to me you are riffing on "Black" and "Radiation" without understanding either phrase.

Rather curious what books or wiki you have read on these subjects.  Probably none, but if some, still curious.


Me? I have first learned of it when studying plank and the UV catastrophe and wave lengths bouncing around in an oven of certain size where no fractional wave lengths exist.


I also have used many gas discharge lamps and was able to measure their spectrums to see the peaks. So this I do know a bit about. Probably read most of the wiki pages on quantum physics and even got a little into the math. Why do you say this?
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Offline Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #43 on: March 09, 2019, 10:28:25 pm »
I imagine a lot of the fluorescence will be due to the shorter visible wavelengths. I remember putting a deep blue plastic box over a linear incandescent lamp as a child to make a poor man's black light. It made lots of  red, orange, yellow and green fluorescent materials glow nicely. It wasn't as good as a real black light, as the visible blue interfered with the effect somewhat and it didn't make white paper glow bright blue, but it was good enough at the time.
 

Offline Beamin

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Re: Getting UV light from a blackbody radiator?
« Reply #44 on: March 10, 2019, 12:02:08 am »
I imagine a lot of the fluorescence will be due to the shorter visible wavelengths. I remember putting a deep blue plastic box over a linear incandescent lamp as a child to make a poor man's black light. It made lots of  red, orange, yellow and green fluorescent materials glow nicely. It wasn't as good as a real black light, as the visible blue interfered with the effect somewhat and it didn't make white paper glow bright blue, but it was good enough at the time.


How did that work? I thought fluorescence was higher wavelength usually ones we can't see being absorbed and reflected at longer wave lengths.  Really hot bulbs do put out some UV especially halogens that need to be behind glass since they are in a quartz envelope to deal with the heat which is clear to UVAB and I think C. But that's less then 1% of the light and the light is like %5 of the total. So almost nothing. Wouldn't the filter have to be purple like woods glass is? Although I have an insane green laser that will fluoresce neon colored paper. That's IR turned to 530nm so no UV, maybe its the brightness on such a small spot?
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Offline Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #45 on: March 10, 2019, 10:22:52 am »
I imagine a lot of the fluorescence will be due to the shorter visible wavelengths. I remember putting a deep blue plastic box over a linear incandescent lamp as a child to make a poor man's black light. It made lots of  red, orange, yellow and green fluorescent materials glow nicely. It wasn't as good as a real black light, as the visible blue interfered with the effect somewhat and it didn't make white paper glow bright blue, but it was good enough at the time.


How did that work? I thought fluorescence was higher wavelength usually ones we can't see being absorbed and reflected at longer wave lengths.  Really hot bulbs do put out some UV especially halogens that need to be behind glass since they are in a quartz envelope to deal with the heat which is clear to UVAB and I think C. But that's less then 1% of the light and the light is like %5 of the total. So almost nothing. Wouldn't the filter have to be purple like woods glass is? Although I have an insane green laser that will fluoresce neon colored paper. That's IR turned to 530nm so no UV, maybe its the brightness on such a small spot?
No all fluorescent material needs it glow is to be excited by a short enough wavelength, normally shorter than the wavelength it emits. It doesn't have to be UV. Blue light will make plenty of neon objects glow and green will cause yellow, orange and red objects to glow. A classic application of this is white LEDs, which use deep blue or violet light to excite a phosphor which produces the longer visible wavelengths, which combine to make white light. Fluorescence can also occur in the infrared band, excited by visible light.

It's also possible for fluorescent materials to emit a shorter wavelength than the incident radiation. Two or more photons in the infrared range can excite a fluorescent material causing emission in the visible spectrum. It only occurs at relatively high intensities, as the second photon has to excite the material, before it has time to fall back to the de-energised state. Infrared laser detector cards, which produce green light from an infrared laser are an example of this.
https://en.wikipedia.org/wiki/Fluorescence
https://en.wikipedia.org/wiki/Photon_upconversion
 
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Offline tooki

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Re: Getting UV light from a blackbody radiator?
« Reply #46 on: March 10, 2019, 11:38:17 am »
How did that work? I thought fluorescence was higher wavelength
No, higher frequency, i.e. shorter wavelength.


usually ones we can't see being absorbed and reflected at longer wave lengths.
We can only see the visible spectrum. Both shorter and longer wavelengths — UV and IR, respectively — are invisible to us.


Really hot bulbs do put out some UV especially halogens that need to be behind glass since they are in a quartz envelope to deal with the heat which is clear to UVAB and I think C. But that's less then 1% of the light and the light is like %5 of the total. So almost nothing. Wouldn't the filter have to be purple like woods glass is?
Yes, basically. It's why the incandescent UV bulbs are so unbelievably, insanely inefficient.


Although I have an insane green laser that will fluoresce neon colored paper. That's IR turned to 530nm so no UV, maybe its the brightness on such a small spot?
Not just brightness, just that some pigments/dyes will react to visible spectrum, too. It's probably exactly how fluorescent colors work. (I'm no expert in this.)


As an aside, just an amusing thing a lot of people don't know: in laundry detergents (except for the special ones for black fabrics), they use optical brighteners, which are literally just dyes that fluoresce blue when exposed to UV, making our clothes glow slightly blue, making them appear bright white! (If you have a UV lamp and a box of powder detergent, the specks of optical brightener glow separately, even!)
 

Offline apis

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Re: Getting UV light from a blackbody radiator?
« Reply #47 on: March 10, 2019, 03:09:32 pm »
That's cool, didn't know there was such a thing as infrared laser detector cards.

Might be worth noting that other things can also excite the atoms and cause luminescence, like electricity (neon lights) or chemical processes (fireflies), but then it's not technically fluorescence any more (electroluminecence, chemiluminescence, etc) even though it's basically the same phenomena.
 

Offline tooki

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Re: Getting UV light from a blackbody radiator?
« Reply #48 on: March 10, 2019, 04:55:05 pm »
That's cool, didn't know there was such a thing as infrared laser detector cards.
Back when people still repaired stuff, they were commonly used for verifying the function of the lasers in CD players, and of infrared remote controls.

Nowadays, a digital camera will do the trick, since they're fairly sensitive to IR. (Except for SLRs, which tend to have very effective IR filters.)
 

Offline Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #49 on: March 10, 2019, 06:22:46 pm »
That's cool, didn't know there was such a thing as infrared laser detector cards.

Might be worth noting that other things can also excite the atoms and cause luminescence, like electricity (neon lights) or chemical processes (fireflies), but then it's not technically fluorescence any more (electroluminecence, chemiluminescence, etc) even though it's basically the same phenomena.
Up-conversion phosphors cost more than cocaine.
https://maxmax.com/shopper/category/9352-infrared-down-conversion-phosphor

 


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