LED/UV combos--wavelength considerations

snovvman

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I found the chart immediately below some time ago and have referenced it for UV wavelength applications:

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I then came upon the chart below from
http://www.theledlight.com. If you compare the two, it seems like someone had the original, and someone else modified it.



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The question is, which chart is more accurate?

I am considering the Streamlight Night Com UV, Nitecore CU6, and Nitecore P20UV.

I am looking for a well-rounded UV light that can be used for viewing animal/bodily fluids, scorpion/insect hunting, AC/leak detection, and just as importantly--document/currency examination. The white LED light makes it a good general carry.

On first blush, it would seem like the Night Com UV, with its dual 365nm and 390nm setup would be ideal. After some research, it seems like a more powerful 365nm can be just as good for all those applications?? This is where I am unable to find definitive information and the charts above only add to the confusion.

I am clear that 365nm is needed for many "real" UV applications while 390nm is closer to visible light (I have read the Night Com UV review comparing the two). Question is, then, why have 390nm at all? Again, the charts above seem to offer no definitive guidance. The CU6 claims 3000mW of UV while the Night Com UV is only 24mW. The P20UV claims to output 320mW.

Will the CU6, with its single (realizing that there is wavelength spill), more powerful 365nm, "outshine" (pardon the pun) the Night Com UV, OR, will the Night Com UV, with its additional 390nm diodes, reveal certain things that the CU6 will not (albeit at a closer distance)?

I would appreciate any information.... Thank you.
 

newbie66

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I myself am confused with UV wavelength and hope someone can recommend a good uv light.
 

jonwkng

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Hi snovvman,

I have both the StreamLight NightCom UV and the NiteCore CU6. Both have their individual merits. I suppose it ultimately boils down to what you intend to do with it.

I got both for the main reason of setting Norland 61 (Optimal UV wavelength 365nm), secondary purposes to go scorpion spotting, having fun with UV flourescence and such. As mentioned, overall output of the NightCom UV mixed spectrum 365nm & 390nm LEDs is very much lower than the reflectored and more powerful set-up on the CU6. And you have correctly mentioned, that there could be aspects of use such as UV flourescence that the CU6 may miss compared to the NightCom UV due to the purely 365nm output on the former.

Do check out subwoofer's excellent NightCom UV review here:-
http://www.candlepowerforums.com/vb/showthread.php?338893-Streamlight-Night-Com-UV-Review

As I always emphasize... UV eye protection is not costly. Do NOT use UV output lights without eye protection. :caution:
 

mmander

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First off, after a fair bit of hesitation, I decided to take a chance on the NiteCore CU6 and I have to say, I am quite impressed... even with the UV emitter. For a brief overview, including a close macro shot of the UV LED and some visible/UV comparison animations, see this post of mine from the other day...

http://www.candlepowerforums.com/vb...P-G2-UV-RGB)&p=4480596&viewfull=1#post4480596

Secondly, I believe this is the link to the spec-sheet of the UV LED being used in the CU6 (found by CPF member hikanio) and if you look at the spectral output curve, calling it a 365nm UV LED is a bit misleading. The peak appears to be just under 385nm with seemingly very little output at 365nm. Certainly, the output curve seems to start at 365nm but it is likely putting out very little there. However the good news is that the LED also outputs very little visible light, so with dark adapted eyes, UV responsive objects appear with excellent contrast, even they only fluoresce slightly.

I have extensively compared the CU6 to a much more expensive EagleTac T25C2 with an LEDengin Gen2 365nm UV LED drop-in module, well supposedly that is the module since that is what I ordered. With the somewhat disappointing output curve of the CU6, I decided to go the route of the EagleTac originally and was very surprised at how much visible white light that UV LED produces, so much in fact, that it washed out any faintly glowing items. Only very strongly fluorescing items were easily visible. Since the CU6 seemed a generally much more useful light, being able to quickly and easily switch back and forth between visible and UV, I decided to get it during an Independence Day sale. In fact, on a recent trip to Arizona during a scorpion hunting session, in part due to not quickly and easily being able to switch between UV and visible, I ended up stumbling slightly and brushing my butt against a Cholla cactus. :eek: Ouch.:fail: It took well over half an hour to not only extract the needles from my butt (not easy when traveling solo!) but also from my shorts. Anyway at that point, marginal UV LED or not, I decided that I would order the CU6 and give it a try during the next good sale I came across!

Imagine my surprise when I got the CU6 and at half the price of the custom EagleTac, it outperformed it! Since then, I have installed a deep violet Rosco gel with only a 4% visible light transmission under the lens of the EagleTac and that has now elevated the usability, in terms of purely strength of UV output, beyond that of the CU6. I am also special-ordering a custom cut Rosco #3660 Permacolor glass dichroic "Cold Mirror" filter to install in the T25C2 in place of the standard glass lens. The filter doesn't allow as much 365nm to pass as a traditional Woods Glass filter, or the now discontinued Rosco #3650 filter, but since the CU6's UV LED seems output in a similar curve to the #3660 filter, it might still work well with the EagleTac, even if it cuts off some 365nm output? If it turns out not to be ideal, I may try some other, harder to find and possibly more expensive options to cut the EagleTac's visible spill.

However, even after "modding" and improving the EagleTac with a filter, I still find the CU6 to be a far more useful flashlight overall, combining white light and UV in one unit. So far, I have yet to find an object that fluoresces only with the EagleTac and not the NiteCore, so right now I don't find the CU6's seeming lack of much true 365nm output to be an issue. :shrug:

I was going to repost an image from my previous forum entry I linked to above but dammit, not only my website currently down where I am hosting all my images, even my web-hosting company's website is totally down! :shakehead That means those animations won't be showing up at the moment, sorry. Oops, scratch that - my site is back up already!

Here is a page from my current Canadian passport, first lit with the CU6's white LED in its lowest regular output mode, then the UV LED...

UV_Passport_anim.gif


By the way, that was taken with a 40mm glass Olight diffuser on the CU6, a filter that hardly cuts down on the UV output at all and works very well. I hope this helps anyone wondering about the CU6's effectiveness, at least for visual or photographic needs...
 
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TEEJ

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I use UV for forensic investigations and other uses, and there are more factors than just wavelength at play.

For example, for an LED, efficiency goes progressively down the tubes when the wavelength gets progressively shorter.

The shorter (365 n is shorter than 390 nm, etc...) wavelengths have higher energy, so things tend to fluoresce more strongly in them.

That means that generally, if something fluoresces at 390 nm, it will do so at 365 nm too, but, if it fluoresces at 365 n, it might not at 390, and so forth.



Now, to see something fluoresce at a given RANGE, say 100' away, the POWER to make a 365 nm beam REACH the target 100' away is a lot MORE than the power needed to make a 390 n beam hit the same target.

So, for scorpions for example, they might glow more brightly when hit by 365 nm at 5' than by 390 nm at less than 5', but, at 100', the 365 nm beam may not have enough range, and the scorp is more visible with the 390 nm beam at that point...and so forth.


So, for a given range, the 365 nm LED set-up is a lot more expensive, as it needs to be a far more powerful set-up to get the same range. Of course, if your target doesn't fluoresce until you get down to 365 nm, and 390 won't excite it enough...you need 365 nm and that's that.


For the few exceptions that only fluoresce AT a particular wavelength, its so rare that for 99% of users, its not worth worrying about....and its safe to assume that for most uses, 365 nm will produce stronger fluorescence than 390 nm can.

So, if you KNOW what your target fluoresces at (money, etc...different bills/country's currency use different dyes, etc) you can use that wavelength or shorter. If RANGE might be an issue, you might use the LONGEST wavelength that it fluoresces at, to get more range with less power/$.

:D
 

mmander

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Hey Teej, thanks for the detailed reply. That all makes a lot of sense. Do you know of any specific items that only fluoresce strongly at 365nm? I would still like to know if my EagleTac light actually has more 365nm output than the CU6?

I have a friend with an Xrite i1 Pro2 and if I recall, it can give spectral distribution output for ambient light measurements. Drat, I just checked the specifications for it and it only reads down to 380nm. Oh well...
 

TEEJ

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Hey Teej, thanks for the detailed reply. That all makes a lot of sense. Do you know of any specific items that only fluoresce strongly at 365nm? I would still like to know if my EagleTac light actually has more 365nm output than the CU6?

I have a friend with an Xrite i1 Pro2 and if I recall, it can give spectral distribution output for ambient light measurements. Drat, I just checked the specifications for it and it only reads down to 380nm. Oh well...

If you mean at 365 but not 390, Ivory or rubies for example...some currencies, etc...a lot actually, but off the top of my head....I'd say just google it. :D



As I said, MOST things will fluoresce at 365 more strongly than at 390 if they fluoresce at 390.
 

mmander

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If you mean at 365 but not 390, Ivory or rubies for example...some currencies, etc...a lot actually, but off the top of my head....I'd say just google it. :DAs I said, MOST things will fluoresce at 365 more strongly than at 390 if they fluoresce at 390.

Thanks, yes that is what I meant - at 365nm but not at 390nm. My dad may have some rough, uncut rubies kicking around since my parents were avid rockhounds. I did do a Google search and came up with this...

http://www.diyphysics.com/2012/04/1...from-395-nm-ultraviolet-leds-and-flashlights/

So, I dug up the same generation of $10 bill and did a comparison. I also included the EagleTac, both filtered and unfiltered so you can see how much white light spill it has...

UV-Compare_10dollar.gif


If this $10 bill behaves the same way as the $5 bill in the link above, and if it's true that the "Bank of Canada" markings only fluoresce under 365nm, then it would appear as though the CU6 does but out a fair bit of 365nm UV light? Maybe the LED used in the CU6 is indeed slightly different (or newer generation) than the one described in the spec-sheet? :thinking:
 
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snovvman

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Wow... thank you to mmander and TEEJ for your knowledgeable and detailed replies. Very helpful! Thank you to jonwkng for your info. It seems like, for a portable UV/LED general-use combo, the CU6 is a better choice than the Night Com, especially after seeing the wavelength distribution.... Again, thanks!
 

TweakMDS

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Interesting to use the violet gel. I have a bunch of rosco sets around, but I only ever use the CTO and straw ones to balance my flashes against tungsten. I think I have a violet and royal blue to play around with. Used that once for a shoot and it came out ghastly :p
I have a new head for my AMC Mule with Nichia 033B coming in, so I can do some more comparisons. Unfortunately I won't be able to use that banknote ^^
 

TweakMDS

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Speaking of safety glasses, I got mine in finally: http://www.conrad.nl/ce/nl/product/678776/CAT-Veiligheidsbril-Tread-112-TREAD112CATERPILLAR-EN-166
I was using amber safety goggles up until now, but they were uncomfortable, mad-scientisty and a bit scratched. These are a million times better :)

I have no consistent way of actually testing the UV protection, but I did find that my Olympus E-PL5 camera combined with 20mm pancake lens is very sensitive to UV light, so maybe I can use that to see if any UV passes. Otherwise I'll have to trust the specs (they don't mentioned UV protection here, but I found the 99.9% on another site for these).
 
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