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Real UV flashlight

Cyparagon

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I'll disassemble my UV LED light when I get a chance and let you know what I find.

Today I compared a UV "blacklight" tube, the flashlight and a 405nm laser dot under the grating.
Fluorescent blacklights will always have a profile something like:



Of course, this is a graph of relative power, not relative brightness.
 
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Atomicrox

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I don't think my grating filters the UV. The decrease in fluorescence with the grating is very small and the reflected spectrum looks justlike the transmitted one.
 

Sigurthr

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So you're saying you have a transmission grating that reflects as well? What sorcery is this?! None of my transmission gratings are reflective and all block <400nm - no fluorescence, zip.


(or you've misunderstood me and you do have a diffraction mirror - you bouce light off it and you can see spectra, like with a CD)
 

Wolfman29

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Sig, I think you're missing that all transmissive material reflect a bit too ;)
 

Sigurthr

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D'oh! Massive brainfart. Now I see what you're saying. Yeah, works great with lasers but I've never seen the effect with lamp + slit.
 

Atomicrox

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This effect works with anything, even regular fluorescent tubes :)

With the sun or a high power flashlight you can even project 4 small rainbows (2 reflective and 2 transmissive).
 

zyxwv99

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One problem with looking at UV is that it's hard to tell why it looks so desaturated. The most obvious cause is a noisy signal. Here at LPF a number of people have posted the spectrometer readings of various laser pointers. They tend to look like tall narrow bell curves with very long, dirty tails. As we learn in statistics, not everything that looks like a bell curve is a true normal curve or Gaussian distribution. The same is true for the sensitivity curves of the rods and cones: in the real world they too have very long, dirty tails. Only in published editions do we see how the graphic designers cleaned them up to make the curves look more Gaussian.

The second complicating factor is eye fluorescence combined with UV opacity, which makes it hard to estimate what we are actually seeing. Last night I was shining various uv lights into my own eyes while looking in a mirror. The lens is quite a bit deeper in the eye than I realized (and changes shape as I change my focus). It doesn't take much to make it fluoresce. Nevertheless, I can see through the fluorescence and see the same eye staring back at me in the mirror.

Yesterday I was reading about this online, including how much UV the lens filters out. At birth it hardly filter out any, but by the time we become adults it's already an OD3 - OD4 filter for anything below 400nm, exact wavelength rising with age. Many elderly persons have trouble seeing violet or even blue. On the other hand, human vision spans a brightness range of ten orders of magnitude, seven for photopic (color) vision, so even OD4 should not be an absolute barrier.

Finally, I've stumbled only some researchers in the field of human UV vision who have discovered that humans possess an opsin known as rhodonine 11 or r(11). The molecule itself has a peak sensitivity at 342nm although in the human eye the peak seems to be something like 353nm. r(11) is apparently scattered among all three cones, but more concentrated in the blue cones.

Since all three of the above factors can contribute to the same result, i.e., seeing desaturated blue when we look at UV, it is hard to separate them. More expensive equipment should take of the first problem. People with aphakic vision solve much of the second problem. (These are people who had early lens implants in the 1970s, before manufacturers realized that artificial lenses need to have UV filtering.)

Ultraviolet light, spectral sensitivity, macular pigments, ocular lens absorbance, scotopic sensitivity, photopic sensitivity, Monet, color vision, rod photoreceptors, cone photoreceptors

PS I am look at diffraction grating mirrors online. Thanks for the tip.
 

Atomicrox

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Update!

Not sure if you guys already know but there are lots of feebayers selling 365nm 5mm LEDs. Seems to be different (and more expensive) than the old ones that did ~400nm. This guy (not the cheapest seller, BTW) even has a comparison picture.

I ordered a couple and will report back when they get here (probably a few months from now, don't wait for it..)
 

zyxwv99

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I have this one: TANK007 TK-566 365nm 1W UV LED Flashlight (1xAA/1x14500) - WorldWide Free Shipping

Tank 007 host. $35.26 from Price Angels. It says 1W output. A single bulb-LED with little square inside that looks like a fine grid when turned on.

No spectrometer, but it lights up the 365 nm security features on British and Canadian currency in a way that higher wavelengths won't. Light looks bluish-gray. Great at finding stains and dirt, but only at close range (2 feet).
 

Atomicrox

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Does it have much visible light on the output?
Mine has a lot of crap all over the visible spectrum. "Dot" looks yellow on a white surface with low fluorescence.
 

Bionic-Badger

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It really helps to have a filter in front of the LED to block out all that extra visible light. Only then did I really appreciate the output of my 365nm LED. Even then, the filter I used wasn't perfect. A true Wood's Glass filter would be best.
 

BShanahan14rulz

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I've seen glass-lensed 5mm LEDs, but just looking at the fluorescence in the photos of the encapsulated LEDs makes me wonder how much visible light is emitted by these compared to typical high power LEDs. Don't know what encapsulant HP UV LEDs use, same as visible HP LEDs?

Anyways, anxiously awaiting review of the encapsulated 5mm :beer:
 




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