# UV light transmittance?



## FrogsInWinter (Nov 2, 2006)

Does anyone have any measurements on UV light transmittance through various lenses? Specifically comparing polycarbonate, lexan, pyrex, borofloat, B270, mineral glass, or UCL to the bare LEDs. From what I've read on wikipedia, glass is more transparent to UV light while polycarbonate inherently blocks most UV light.

I'm going to drop a UV TerraLUX Ministar 2 into a 2aa mini-mag and I'm wondering if there's a big difference between UV light transmittance vs. visible light transmittance through different lenses. After all having a UV LED behind a lens that blocks most/all UV light doesn't make a whole lot of sense.

Would it be a better idea for me to get a UV light that has the LEDs exposed? Like the ones sold on Light Hound or Advancedmart? Thanks in advance for any helpful information!


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## macforsale (Nov 2, 2006)

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## Sub_Umbra (Nov 2, 2006)

FrogsInWinter said:


> Does anyone have any measurements on UV light transmittance through various lenses? Specifically comparing polycarbonate, lexan, pyrex, borofloat, B270, mineral glass, or UCL to the bare LEDs. From what I've read on wikipedia, glass is more transparent to UV light while polycarbonate inherently blocks most UV light...


I don't have any measurements. I'd like to see them, too. 

While glass _itself_ may block less UV than other materials, I've read that the AR coatings on UCLs attenuate UV and are counterproductive in that use. 

IIRC InReTech used to advise customers to use M/\G's stock polycarbonate window with their UV drop-ins. I'm not sure, though.

Some CPFers have noted that the Carlco optics tend to attenuate UV while the Frean optics do not. They have stated that a visibly noticable color change in the UV beam will accompany this attenuation. (The Carclo optics glow green instead of purple.)

If you do find any hard data on UV transmission rates with various materials be sure to post it. It's a very interesting subject.


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## elgarak (Nov 2, 2006)

As a rule of thumb, glass DOES NOT transmit UV. Period. That's the rule that I as physicist use. All glasses that do are specially formulated (and are technically not glasses, but look and feel like it). You will know it when you buy it, 'cause it's frickin' expensive.

Now, LEDs are just barely in the UV. Mostly they emit around 400nm, which is near UV purple. I have seen flashlights emitting ~375 nm. Bare LEDs may go down to 350nm. That's all just beginning of UV, so most glasses MAY work. However, I would recommend using LEDs bare, especially the lower wavelength ones, since they are probably not very bright yet, so you wanna avoid any absorbance.


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## cdosrun (Nov 2, 2006)

Absorption at UV wavelengths is worth noting, but I don't think it is too much of a problem with the longer wavelengths as Elgarak noted. Nichia do use quartz 'glass' on their focused UV leds as quartz has very low attenuation in the UV spectrum.

Optical glass should be good to around 335-350nm, Acrylic down to about 300nm and quartz, well into the UVc range (140nm or so). An idea is probably to Google for something like "acrylic cuvettes nm" substituting acrylic for the material in question. Cuvettes are the little receptacles for samples when measured spectrographically in the lab.


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## soapy (Nov 2, 2006)

Agreed. The "UV" is generally visible purple light and very long wavelength UV, which glass will let through just fine. 

Do tests on anything neon at a bit of a distance, and use the return from your neon target to tell you if anything much has been cut out when you add your test material.


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## Sub_Umbra (Nov 3, 2006)

I was thrashing about on the web and I found a few graphics that _may_ have a bit of interesting info here and there. Or not. I added the URL of each graphic to the bottom of each one.







*This one* isn't big but it's too wide for this page.






I know that this stuff isn't particularly _pointy_ but I thought it was interesting enough to put up.


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## NewBie (Nov 3, 2006)

Also check this out:


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## hank (Nov 3, 2006)

Are any of the flashlight lens sellers reading this?

If so, please consider sending samples of your various lenses to Craig at LEDmuseum -- he's been posting the spectra of various light sources.


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## FrogsInWinter (Nov 3, 2006)

Wow, thanks to everyone for all the great info. I also posed this question to Chris at Flashlightlenses.com and he gave similar answers to what's been posted here. He was also nice enough to provide me with this chart regarding light transmittance for their UCL lenses:





(Used with permission)
Sorry if the picture is a little small, but you can save it to your computer and zoom in using any kind of picture viewer.


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