Author Topic: Getting UV light from a blackbody radiator?  (Read 1360 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, 03:18:59 pm »
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, 03:44:30 pm »
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, 04:52:13 pm »
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, 06:18:38 pm »
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, 08:08:04 pm »
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, 08:33:56 pm »
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, 08:37:03 pm by Nerull »
 

Offline jimdeane

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Re: Getting UV light from a blackbody radiator?
« Reply #31 on: January 15, 2019, 05:50:39 am »
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 15, 2019, 05:52:50 am »

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 16, 2019, 02:52:49 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.
 
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Offline Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #34 on: January 16, 2019, 03:42:28 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.
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 16, 2019, 04:38:08 am »
JimDeane's "fake" looks identical to the two brands I have.  I can't guess at motivation, but clearly it wasn't accident.
 

Online apis

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Re: Getting UV light from a blackbody radiator?
« Reply #36 on: January 16, 2019, 07:11:44 am »
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 16, 2019, 08:20:34 am »
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
 


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