Ultra Violet and Infrared question...

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evahle
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Ultra Violet and Infrared question...

Post by evahle » Wed Jan 07, 2009 3:21 am

I recently received 105 LEDs(7colors, 15each). High brightness types. It had Ultra-Violet LEDs as well. I haven't had any of these before and decided to experiment with them.

I remember in the 1960s the Black Light craze, where you'd use Ultra-Violet in a dark room, where you'd paint the walls and ceiling with flouescent paint(if I remember correctly). That was pretty cool! The paint would glow as if you were in outer space. What I also remember was, if anyone came into the room wearing white, their white clothes would also seem to glow.

I've also noticed the night-viewers, night-scopes and infrared viewers available out there. I've also noticed the credit card size infrared detector that I bought from MCM and how it glows orange when infrared strikes the little area on the card.

I decided to shine the ultra-violet LED onto my workbench, then move it over onto a white piece of paper. On the workbench it had a dull purple glow. On the paper, it was a bright blue. hummm. I then tried the same experiment with a Blue LED, and it was a bright blue on the workbench, as well as the piece of paper. In fact the blue on the paper didn't look much different than the Ultra-Violet on paper.

With Infrared turning orange and Ultra-Violet turning blue, I wonder how this works. So my question is; How does a simple piece of white paper change the wavelength of light? I know very little on the subject, and it may have a simple answer, but I haven't run across anyone asking this before. Yea, I could search the internet, but I thought this might be a little thought prevoking and I would be happy to hear anyone's opinion. Thanks!

evahle :smile:

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MrAl
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Post by MrAl » Wed Jan 07, 2009 3:37 am

Just a quick note of warning here...

Ultraviolet light can cause blindness because the eye does not
react to the level of light like it does for ordinary light, so the
retina gets banged hard.
Be very careful.

Some info...
http://en.wikipedia.org/wiki/Fluorescence
LEDs vs Bulbs, LEDs are winning.

sghioto
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Post by sghioto » Wed Jan 07, 2009 5:37 am

I don't think it's changing the wavelength. Any thing white reflects all colors. The infrared LED probably has a small amount of output in the red/orange band that shows up when held next to the paper, same for the ultra violet in the visible blue wavelength.

Steve G.

farsideeng
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Post by farsideeng » Wed Jan 07, 2009 6:55 am

Many papers have a whitener added which fluoresces in the blue.

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dacflyer
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Post by dacflyer » Wed Jan 07, 2009 11:08 am

i searched in vain to try to find a white paint that is reactive to blacklight
i never had any luck. dyes will react but paint pigments won't, well at least not with house paint. i was wanting to paint my room once with white reactive paint, so that when i turned on a black light on. the room would glow a brillant blue.. i found a whole case of 4' blacklights that was being discarded from a flood, but the lights were still new and only the paper cover was ruined..them lamps cost baout $25.00 in most places..and i got 40 bulbs in a case :P

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haklesup
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Post by haklesup » Wed Jan 07, 2009 12:10 pm

Evidently UV lLEDs come in colors ranging from 360nM to 255nM
http://www.roithner-laser.com/LED_diverse.htm
Do you know what you have?

Acording to Wiki, a blacklight bulb source can be from 450nM to 310nM with the common black light you speak of apparently at 370nM
http://en.wikipedia.org/wiki/Black_light

It seems reasonable that the flourescence you see in white clothing should work for both the LED and fluorescent bulb

Laundry bluing seems to help white clothing really shine. Mixing some into paint might help. Though since the base in most modern paint is Zinc Oxide, a rather inert low energy substance, I am not surprised it doesn't have the electron valance structure to put an electron in a high enough energy level to produce flourescence A specific UV or blue dye would be required.

More expensive high resolution ink jet paper is more likely to have the kind of additives needed to make it flouresce as opposed to the cheapest stuff. Not all paper is equal and thats clear even without a black light.

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Re: Ultra Violet and Infrared question...

Post by Bigglez » Wed Jan 07, 2009 12:35 pm

evahle wrote: I decided to shine the ultra-violet LED onto my workbench, then move it over onto a white piece of paper. On the workbench it had a dull purple glow. On the paper, it was a bright blue.
The UV light spectrum is divided into different wavelengths.

The UV LEDs are not the same as the UV discharge
lamps popular in Discos, etc.
evahle wrote:How does a simple piece of white paper change the wavelength of light?
The printer paper and other 'white' products contain
phospors that convert visible light (and UV-A or
"BLB" bulbs) to visible blue - making them appear
brighter to the eye.

Discharge lamps produce UV-C (Germicidal lamps)
and are used to stimulate phosphors found in neon
and CRTs.

White LEDs include phosophor belnds to emit 'white'
from the native UV or blue light emitted by the die.

When I worked in the CRT factory we use UV-C
lamps to identify phosphor materials used for
screens.

The light from some UV sources is hazardous to
the eye (causes cornea burns, possibly blindness).

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dacflyer
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Post by dacflyer » Wed Jan 07, 2009 6:26 pm

bigglez >> you said... Discharge lamps produce UV-C
(Germicidal lamps)
and are used to stimulate phosphors found in neon
and CRTs.

i have one of these lamps, and i used it to identify neon tubes colors when i used to make neon, it was a small ball shaped bulb with a small filiment in it..it worked great, i also have a small 6 watt UV-C lamp
but it does not do the same... both lamps are clear, and you can clearly see the filiment glow, so i am wondering why they both do not work the same, same with clear neon with argon gas (no phosphers) if i hold the clear neon to another stick of glass with coating init,, it also does not show color of the coating.. does the arc/glow have to be in contact with the coating to make it glow ? or does the UV have to be at a exact wavelength? even tho all the glows look exactly the same ? i figgured the discharge glow in a flourescent lamp or neon is the same ,, or ?
enlighten me if you can..

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Post by jimandy » Wed Jan 07, 2009 6:56 pm

As an aside, scorpions fluoresce green. Really bizarre. I bought a UV light to look for the little boogers in my basement.
"if it's not another it's one thing."

Bigglez
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Post by Bigglez » Thu Jan 08, 2009 12:52 am

dacflyer wrote:bigglez >> you said... Discharge lamps produce UV-C
(Germicidal lamps)
and are used to stimulate phosphors found in neon
and CRTs.

i have one of these lamps, and i used it to identify neon tubes colors when i used to make neon, it was a small ball shaped bulb with a small filiment in it..it worked great, i also have a small 6 watt UV-C lamp
but it does not do the same...
Yep, I found that out (the hard way) too!
The gadget for inspecting open "neon" glass with coating
has to be UV-C (Germicidal). The glass used in these is
actually quartz (hard glass), while neon is soda-lime leaded
glass (aka "soft glass").
Neon glass can be melted in gas/air fires, as you know.
Hard glass needs O2 for hotter flame, and protective
eyewear, due to the UV form the flame.

I hoped to use the UV LED to inspect phosphors, but
of course it didn't work!

Soft glass blocks UV-C, and so an argon or neon-mercury
tube won't light up another tube (or loose phosphor
powder). Nor will a black light (UV-A) tube, which uses
"woods glass" to allow the UV-A wavelength to pass.

Some disco bulbs had a filament as a ballast to the
cold cathode capsule, and the filament can be seen
through the blue glass. These run very hot. A tube
(fluorescent lamp) with BLB is much better.

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dacflyer
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Post by dacflyer » Tue Jan 27, 2009 6:43 am

some high power blacklights now use a 400 watt mercury lamp and a BLB glass lenz they seem to be powerful, i have seen a motel near here use that scheme to light up the outside of the building.. looked really cool. made the motel look like a giant ELD :P

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