Ultraviolet Light Wavelengths

[martynball]

Hey, i'm no expert in science so I don't know what category light comes under.

 

But here is a question I asked on Yahoo Answers but i'm not getting a reply, plus there answers aren't always trustworthy.

 

I need a LED torch that will show drugs + blood.

Currently I have one which shows the security markings on UK driving licenses which according to Wiki is:

 

230-365 nm: UV-ID, label tracking, barcodes

 

For some reason this does not show the markings on UK notes, like it should do, i'm guessing money needs a different wavelength?

Now according to the same wiki page to see blood + drugs you need the following wavelength:

 

200-400 nm: Forensic analysis, drug detection

 

So my current one that should be between 230 - 365 is it works on driving licenses, should work on blood? It's between 200 - 400nm :S

Edited August 12, 2012 by martynball

[martynball]

How active is this forum?

[swansont]

How active is this forum?

Pretty active, but you ask a fairly specific question.

[Moontanman]

I doubt there is a wave length of UV that will show "drugs", the question is not specific enough... What drugs? What concentration?

[John Cuthber]

I can cite at least on psychoactive drug that has no accessible UV absorption, so the question is moot.

I also generally find that I can see blood perfectly well under normal visible light. The stuff is bright red.

Also, the range from 200 to 400 nm covers pretty much the whole range of UV that's going to be any use at all. (longer than 400 and it's visible, shorter than 200 and it gets absorbed by oxygen in the air.)

So this "200-400 nm: Forensic analysis, drug detection" is pretty meaningless.

Add to that the fact that UV leds for wavelengths less than about 350nm are getting into the range of seriously expensive and you are probably on a hiding to nothing.

 

What are you actually trying to achieve?

Edited August 13, 2012 by John Cuthber

[Fuzzwood]

You expect the stuff to light up under UV? It doesn't.

[martynball]

Money has marking on it that glows under UV light, as do other forms of identification. For some reason the UV LED's I have do not cause the marking on money to glow, but it does on a driving license.

 

Also, cocaine does glow under a certain wave length, of course I don't have any to test my led's on so I was wondering if anyone knew if my LED's would work.

 

And of course i'm not talking about visible blood, but blood that has been attempted to wash up, like they do in crime scene's although they use some spray to amplify the effect.

[martynball]

?

[Ronald Hyde]

What you're probably looking for is a lamp that will make the materials you're talking about 'fluoresce' as opposed to merely reflecting the light. The material fluoresces and reflects at much lower energy than that required to make fluorescence occur, because it's a two step process. The molecule absorbs the UV energy, drops down to a lower lever, then drops down again to the ground level by emitting the rest of the energy.