Author Topic: Getting UV light from a blackbody radiator?  (Read 1372 times)

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Offline Beamin

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Getting UV light from a blackbody radiator?
« on: January 06, 2019, 05:17:39 am »
Postulate this: If a tungsten light bulb filament gives off black body radiation how do they make black light bulbs (the woods glass type) and "halogen" lights that give off UV? The UV catastrophe problem says that you can't do that.  I have a feeling "black light" may not be UV but rather extreme purple that our eyes can't see, but its still color light right before the photon has enough keV to ionize. This would be the same trick in woods glass fluorescent black light tubes, as the envelope would have to be quartz to let out UV, or does silica glass pass UVA just fine? Wouldn't the best black light be a fluorescent quartz glass tube with a UVB/C filter that also cuts most of the shorter UVA wave lengths?

Fun Story, my bed room as a kid had four 4' black lights on the edge of the ceiling with tin foil reflectors on the wall. The room looked normal day or night, but when you turned on the black lights you could see the walls were painted in laundry detergent antifreeze, dilute highlighters, and some other toxic chemicals that look clear under normal light. We used to give our friends way too many hits of LSD or mushrooms bring them in the room they saw many times in ordinary light, then turn on the black lights and watch their minds explode!!! Wish I had pictures film cameras didn't show that stuff well or rather not easily like a digital camera would.


 
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Offline helius

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Re: Getting UV light from a blackbody radiator?
« Reply #1 on: January 06, 2019, 06:00:51 am »
The simple answer is that "woods lamps" are not incandescent at all. They are gas discharge lamps with an integrated incandescent ballast.

See video here:
https://youtu.be/aBrLeOVBCaE?t=4m0s
« Last Edit: January 06, 2019, 06:43:09 am by helius »
 
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Offline tooki

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Re: Getting UV light from a blackbody radiator?
« Reply #2 on: January 06, 2019, 06:28:03 am »
No, there really are incandescent blacklight bulbs using wood’s glass. I had one as a kid.

They work, they’re just ferociously inefficient, since less than 0.1% of the energy is UV.

See https://en.wikipedia.org/wiki/Blacklight#Incandescent
 

Online Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #3 on: January 06, 2019, 06:54:41 am »
Incandescent lamps do emit a tiny amount of UV. The higher the filament temperature, the more UV they'll emit, at the expense of a shorter life.

Ordinary glass passes UVA pretty well. It just blocks the shorter UVB and UVC wavelengths, which is good for protecting the eyes and skin.

The shorter visible wavelengths, blue, indigo and violet, cause fluorescence at longer wavelengths: green, yellow, orange and red. In fact the longer end of the visible spectrum will excite fluorescence to some degree but it will be infrared.

Digital cameras respond poorly to UV but I don't know how they compare to colour film. Old back and white film will respond in the UV but camera lenses filter it out.

The mid to lower end of the UV spectrum, is not ionising. Incandescent lamps do not emit and ionising radiation.
https://en.wikipedia.org/wiki/Ionizing_radiation#Definition_boundary_for_lower-energy_photons
 

Offline CatalinaWOW

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Re: Getting UV light from a blackbody radiator?
« Reply #4 on: January 06, 2019, 08:47:12 am »
Agree.  Those cheap tungsten UV lights run hot and live short lives.  Produce little UV.  And usually have some sort of filter to block the IR and visible which is produced in far greater quantities.  It would be interesting to know if this is some sort of absorption filter or a cheaply produced interference filter.  My bet is for the absorption type.

Remember, while there is a peak wavelength for each temperature of emitter, and the reduction in intensity beyond the peak is why the UV catastrophe doesn't occur, there is no wavelength that has zero output, no matter what the temperature.  You just have to use lots of zeros to describe it.
 

Offline T3sl4co1l

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Re: Getting UV light from a blackbody radiator?
« Reply #5 on: January 06, 2019, 08:58:38 am »
Yeah, the UV side of the curve drops off exponentially, or something like that.  So there's a nonzero chance of, say, receiving a 1keV photon from room-temperature material..... it's just "impossible" (10^-100 likelihood, say).

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Online Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #6 on: January 06, 2019, 09:00:19 am »
Agree.  Those cheap tungsten UV lights run hot and live short lives.  Produce little UV.  And usually have some sort of filter to block the IR and visible which is produced in far greater quantities.  It would be interesting to know if this is some sort of absorption filter or a cheaply produced interference filter.  My bet is for the absorption type.

Remember, while there is a peak wavelength for each temperature of emitter, and the reduction in intensity beyond the peak is why the UV catastrophe doesn't occur, there is no wavelength that has zero output, no matter what the temperature.  You just have to use lots of zeros to describe it.
They use Wood's glass, which passes infrared, UVA and some violet and a tiny amount of far red.
https://en.wikipedia.org/wiki/Wood%27s_glass

https://www.uqgoptics.com/materials_filters_schott_uvTransmitting_UG1.aspx
« Last Edit: January 06, 2019, 09:41:57 am by Zero999 »
 

Offline Beamin

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Re: Getting UV light from a blackbody radiator?
« Reply #7 on: January 06, 2019, 10:12:21 pm »
Agree.  Those cheap tungsten UV lights run hot and live short lives.  Produce little UV.  And usually have some sort of filter to block the IR and visible which is produced in far greater quantities.  It would be interesting to know if this is some sort of absorption filter or a cheaply produced interference filter.  My bet is for the absorption type.

Remember, while there is a peak wavelength for each temperature of emitter, and the reduction in intensity beyond the peak is why the UV catastrophe doesn't occur, there is no wavelength that has zero output, no matter what the temperature.  You just have to use lots of zeros to describe it.
They use Wood's glass, which passes infrared, UVA and some violet and a tiny amount of far red.
https://en.wikipedia.org/wiki/Wood%27s_glass

https://www.uqgoptics.com/materials_filters_schott_uvTransmitting_UG1.aspx


I thought you were Hero999 not Zero999 Did you change it while I was on holiday? Or am I losing my mind?
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Online Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #8 on: January 07, 2019, 06:28:34 am »
Yes, I changed it while you were away around Christmas time.
 

Online Brumby

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Re: Getting UV light from a blackbody radiator?
« Reply #9 on: January 07, 2019, 12:47:16 pm »
From Hero to Zero ...                                                               
 

Offline Beamin

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Re: Getting UV light from a blackbody radiator?
« Reply #10 on: January 07, 2019, 08:17:58 pm »
From Hero to Zero ...                                                               

Quagmire: 
"Hey lady, why don't you ditch the zero and go home with a hero?" He then gets punched in the face.
"Alright!"


I'm glad someone noticed I was gone, I bet people were like "Ahhhhh, so nice and quiet here, no stupid questions or repetitive posts followed by apologies and excuses."


Zero99 is a cooler name I think.
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Online Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #11 on: January 07, 2019, 09:39:00 pm »
Yes, I thought Hero was a bit narcissistic. I can't remember why I chose it in the first place. I've been unhappy with it for awhile, but stuck with it because I didn't know it could be changed without closing my old account and opening a new one. Recently, I learned it's possible to change my name, with the permission of a moderator, so I did.
 

Offline Beamin

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Re: Getting UV light from a blackbody radiator?
« Reply #12 on: January 10, 2019, 10:01:19 pm »
Yes, I thought Hero was a bit narcissistic. I can't remember why I chose it in the first place. I've been unhappy with it for awhile, but stuck with it because I didn't know it could be changed without closing my old account and opening a new one. Recently, I learned it's possible to change my name, with the permission of a moderator, so I did.

If only doing it in real life was that easy. Its actually easier to change your gender on your birth cert. then your name. It depends on the sate but you don't even need documentation from your doctor, you just say "I identify as this sex now" and they change it. Which is great because some people live as females but don't want to have surgery, like myself. Has nothing to do with the state you currently reside in. So if you were born in some shithole state like Mississippi, you can move away but will always be affected by its laws. Of course you could always delete your account in real life and create a new one but that only works if you are Buddhist.
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Offline apis

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Re: Getting UV light from a blackbody radiator?
« Reply #13 on: January 12, 2019, 08:54:56 am »
A good example of an incandescent lamp that emits UV is the sun (which has an equivalent black body temperature of 5778 K)


https://en.wikipedia.org/wiki/Black-body_radiation

The black line represents what classical mechanics intuitively would predict, which obviously didn't agree with measurements. That problem was called the UV catastrophe.

The solution was to make some, for the time, rather strange assumptions. They were the first clue to modern quantum physics and thus are very important historically. Those assumptions give a so called black body radiation spectra which agrees perfectly with measurements. The other lines show black body radiation spectra for different temperatures. As can be seen in this graph that means there is a fair amount of UV from the sun (most of which is blocked by the ozone layer).
« Last Edit: January 12, 2019, 08:58:40 am by apis »
 

Offline helius

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Re: Getting UV light from a blackbody radiator?
« Reply #14 on: January 12, 2019, 09:18:20 am »
This is an example of the type of lamp I was talking about:
http://pen-ray.uvp.com/highintensitylamps.html


It is a 90 W lamp, with an irradiance of 8500 uW/cm2 at 2 inches. It is a gas-discharge lamp with an incandescent ballast (gas discharge lamps have negative resistance and require ballasts to limit current consumption). The user can tell this immediately, because the UV output doesn't begin until the lamp has been "lit" and warming up for about 30 seconds. The bulb also has a safety cutout to prevent hot striking and so it may shut off during use, which is not true of incandescents.
 

Offline jimdeane

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Re: Getting UV light from a blackbody radiator?
« Reply #15 on: January 12, 2019, 09:58:31 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.
 

Offline tooki

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Re: Getting UV light from a blackbody radiator?
« Reply #16 on: January 13, 2019, 01:03:39 am »
This is an example of the type of lamp I was talking about:
http://pen-ray.uvp.com/highintensitylamps.html


It is a 90 W lamp, with an irradiance of 8500 uW/cm2 at 2 inches. It is a gas-discharge lamp with an incandescent ballast (gas discharge lamps have negative resistance and require ballasts to limit current consumption). The user can tell this immediately, because the UV output doesn't begin until the lamp has been "lit" and warming up for about 30 seconds. The bulb also has a safety cutout to prevent hot striking and so it may shut off during use, which is not true of incandescents.
:palm:
Nobody was disputing that gas-discharge UV lamps exist.

You claimed that the incandescent UV lamps must be gas discharge, and this claim is demonstrably untrue. Disproving this claim says nothing whatsoever about the existence of gas discharge UV lamps.
 

Offline tooki

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Re: Getting UV light from a blackbody radiator?
« Reply #17 on: January 13, 2019, 01:06:22 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.
So it was what, an incandescent heater? :D

Just to be clear, incandescent UV lamps are so unbelievably inefficient at UV that I wouldn‘t be surprised if the ratio of IR to UV from those exceeds the dynamic range of some measurement gear.
 
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Online Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #18 on: January 13, 2019, 01:57:57 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.
So it was what, an incandescent heater? :D

Just to be clear, incandescent UV lamps are so unbelievably inefficient at UV that I wouldn‘t be surprised if the ratio of IR to UV from those exceeds the dynamic range of some measurement gear.
I agree.

Does this one actually cause things to fluoresce?

What colour does it appear when lit? No doubt it's cherry red, rather than the usual dim violet glow produced by real black lights, as it emits more in the deep red, than violet end of the spectrum.
 

Offline T3sl4co1l

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Re: Getting UV light from a blackbody radiator?
« Reply #19 on: January 13, 2019, 02:20:29 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.

Why would you plot it on linear axes?  The UV component is a few pixels here.

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Online Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #20 on: January 13, 2019, 04:36:51 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.

Why would you plot it on linear axes?  The UV component is a few pixels here.

Tim
No doubt it's the default seeting for the software connected to the spectrometer, which might not have a wide enough dynamic range to see the UV as well as the IR.
 

Offline helius

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Re: Getting UV light from a blackbody radiator?
« Reply #21 on: January 13, 2019, 07:12:33 am »
:palm:
Tooki:
I showed you mine—now you show me yours.
 

Offline tooki

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Re: Getting UV light from a blackbody radiator?
« Reply #22 on: January 13, 2019, 05:48:44 pm »
:palm:
Tooki:
I showed you mine—now you show me yours.
What are you, 10?!

I already linked to evidence in my first reply.
 

Online Zero999

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Re: Getting UV light from a blackbody radiator?
« Reply #23 on: January 13, 2019, 08:30:50 pm »
:palm:
Tooki:
I showed you mine—now you show me yours.
I presume he doesn't have a crappy blacklight incandescent lamp. No doubt if he has or gets a blacklight, it'll be a fluorescent or LED type.

I know blacklight incandescent lamps exist. Maplin used to sell them. I have a blacklight CFL which wasn't that much more expensive and no doubt is 1000 times more efficient. The glass bulb is ordinary, uncoloured glass, coated with a blacklight filter, probably Wood's glass. The only issue is the end of the tube only has a thin layer of filter, so it produces more visible light, than a standard linear blacklight blue fluorescent tube.

I have contemplated buying a blacklight incandescent lamp, but only so I can use the glass bulb as a filter for a UV LED, as I couldn't find a cheap Wood's glass filter. In the end I didn't bother, because I'm not confident in my ability to cleanly and safely cut the base off the bulb without breaking it. I thought about trying on an ordinary incandescent lamp to practise, but I've read that Wood's glass is more difficult to work with.
 

Offline CatalinaWOW

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Re: Getting UV light from a blackbody radiator?
« Reply #24 on: January 14, 2019, 03:04:01 pm »
More proof of existence.  I dug into the bin of bad buys and came up with two brands of incandescent black light bulbs.  They were originally purchased (at a second hand shop) in an attempt to come up with a cheap eraser for UVEPROMs.  Yeah it was a long time ago.  They didn't work.  But about the same time I purchased a 6 inch fluorescent tube reputed to be UV.  Which wouldn't erase the PROMs either after four hours of exposure.  The incandescent bulbs give no visible sign of causing florescence even in a totally dark room, so at least for me these have been a total failure, though I don't doubt for a minute that there is some minute amount of UV emitted.

The bulbs are very similar in appearance, but one is marked as made in China, while the other is marked as made in Korea.  Since these were purchased before trade relations with China were fully normalized it is possible that they were both made in China, with one having been exported first to Korea before coming to the USA.

The photograph of one of them in operation shows clearly that they are not a gas discharge bulb, but a fairly standard tungsten filament type.

These bulbs run very hot.  My pyrometer shows the top of the bulb at 155 C with the sides running 95 to 100 C.  Normal incandescent bulbs measured with the same pyrometer measure about 65 C on the upper surface and 40 C or so on the side.  That leaves a potential application for these things as fingerprint removers.

 
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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.
 

Online 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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Online 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.
 

Offline 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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