UV/IR transmission of lenses & stuff?

Well, I searched here and on the web but didn't find anything very helpful.

I'm wondering if anyone knows or has a link to a site where I can find out the IR & UV transmission characteristics of various materials used in flashlight lenses & bulbs?

I think that because I can buy a very cheap pair of plastic sunglasses that advertise "Blocks UV-A & UV-B" (not that I know what A & B are on the spectrum) that most plastic must have good blocking in itself.

I'm just curious about why, for example, we can have a UV version of the ARC flashlight if its LED is made with a dome of clear stuff (epoxy)?

And some of those HID lights advertise putting out UV. Does that mean that they must have something other than a plastic lens?

What about quartz, used for some bulbs? Does that absorb in the UV or IR?

What about glass? That can't transmit IR or else the inside of my car wouldn't heat up so much from the sunlight would it? But if it doesn't transmit IR, then why does the light beam from my fancy flashlights feel so hot?
[edit] Oh wait, glass must transmit IR because heat lamps probably have housings of regular glass. Hmmmm. Now I'm realizing I just have no clue how that greenhouse effect works. (If only I had a memory)

Questions like that are what I'm wondering...

binky,

Most thermoplastics are very transparent to IR, even when colored with any pigments other than carbon black. I'm not sure about UV transmittancy. Quartz glass passes UV but ordinary soda (window) glass doesn't. It's supposed to be hard to get sunburned indoors through a patio glass window. That's the limit of my limited knowledge /ubbthreads/images/graemlins/smile.gif .

Larry

That's good info -- thanks!

So I guess those HID light manufacturers such as Xenonics touting the NHII for forensics use might be using a quartz lens? Hmmm. That sounds pretty expensive. Of course, the NHII is expensive.

I'm still wondering about the other stuff. What about the epoxy over the UV LED, such as in the Arc UV. I guess epoxy must pass UV.

If anyone has any links to a web site with this transmittance info, that'd be really helpful too.

binky,
The "plastic" on conventional LEDs like 5mms isn't epoxy, it is typically acrylic (aka plexiglass). It is injection-molded, and I believe fairly UV transparent. I am unaware of a good site for optical transmissivancy (sp?) at various wavelengths of thermoset and thermoplastic materials. (But would sure like to bookmark one! /ubbthreads/images/graemlins/grin.gif )

Larry

I think most glass will pass a fair amount of UV unless it is coated or impregnated to do otherwise. The whole "sunburn inside" thing probably holds true because most glass used in structures is designed to reject UV for energy efficiency.

Thanks Chris. BTW -- you don't happen to have any links to data on transmission, do you? I'm hoping that you might know some url's since there might be some info buried in manufacturer's sites that you've visited for the lens making.

I'm just really curious of UV/IR through
Polycarbonate = ?
Lexan = ?
Boro... quartz...

UV A 315 - 400nm
UV B 280 - 315 nm
UV C 100 - 280 nm

Optical glass

http://www.cvilaser.com/static/tech_optmaterial.asp

Plastics

http://irc.nrc-cnrc.gc.ca/cbd/cbd213e.html

Dug all this up a whiloe back to do with a,erm, discusion about blacklight effects on a newsgroup.

HTH
Adam

Wow, thanks Adam! /ubbthreads/images/graemlins/smile.gif

Those graphs are great, and so's this text:

[ QUOTE ]
Optical properties. -- Both thermoplastics and thermosetting plastics may be highly transparent, opaque, or have any degree of clarity and light transmission in between. The total solar energy transmission may run as high as 90% with 92-93 in the visible region (400 to 750 nm).

Transmission in the visible, ultraviolet (UV) and infrared (IR) is a variable (depending on the wavelength) and can be controlled to a large extent by composition. Thus the UV transmission can be made high to achieve beneficial effects such as killing germs, or it may be cut off entirely by using UV absorbing additives to reduce deterioration of the plastic. Similarly a substantial portion of the heat-inducing In light can be either transmitted or absorbed, depending on the composition. Like glass, most clear plastics used as glazing provide a 'greenhouse effect' because the solar radiation that is converted to heat in an enclosure is not transmitted back to the exterior. Soils, plants and frames inside the greenhouse absorb this radiation during the day, and reradiate it as heat energy at night. The enclosure (glass or plastic) blocks the passage of the IR radiation to the outside air, thus providing a small but significant source of heat and reducing the cost of the operation. Since clear plastics transmit approximately as much solar radiation as glass and also retain heat, their use as green- house enclosure material is widespread.

[/ QUOTE ]

So regular glass doesn't transmit IR. I always thought the only reason Surefire & others might have been using Pyrex for their flashlight lenses was because it could handle thermal shock better than glass. Now I see that maybe also it's necessary to let the IR light out so the flashlight can be useful for nightvision applications. And a heatlamp housing must also not be glass as I'd always thought it was.

I'm just getting started looking this stuff over. Thanks again to all for the responses! There's more science involved in the lens choice than I thought!!

Chris (flashlightlens) I see this IR transmission is another reason to keep selling the Borofloat lenses. (Maybe this is another good info point to add to the web page?)

So Lexan doesn't transmit IR and Pyrex does.

I wonder, as the mechanics of not transmitting IR, if a Lexan lens reflects or absorbs the IR. If it absorbs it, that would explain why people might experience a melted lens. I just couldn't understand how a lens could get melted (as people are complaining/worried about such as with G2 & P61 lamp here and in lots of other threads) since it was hard for me to imagine that the entire front housing of the G2 was getting above the melt temp of acrylic (acrylic has melt temp ~400F, BTW nylon=nitrolon has melt temp ~500F).

[ QUOTE ]
tvodrd said:
......
The "plastic" on conventional LEDs like 5mms isn't epoxy, it is typically acrylic (aka plexiglass). It is injection-molded, and I believe fairly UV transparent.........

Larry

[/ QUOTE ]

Larry,

Are you sure about this? I was under the impression that the envelopes of say the Nichia LED's are an epoxy. Further I understand that UV will degrade epoxy and this is one of the reasons that the UV LED's don't have a long life. Nichia has some metal housed UV LED's and their new 2 watt has a glass lens instead of plastic.

- Don

Intuitively, it seems that a thermoset epoxy would be better suited to mold over a hotspot than a thermoplastic acrylic which could melt at some point, but maybe this is a question for our friendly ledmuseum guy. (I did a quick specific scan over the Craig's website for this info, but didn't find it in, for example the faq section describing how led's are fabricated)

McGizmo-
I have been batting zero lately /ubbthreads/images/graemlins/twak.gif I just took a generic clear T 1 3/4 and plunged it into Weld-On #3 acrylic solvent cement and no effect. I repeated with a Nichia, and again no effect. Definately a thermoset and most likely an epoxy! This also explains why when I slipped with the soldering iron and hit an LS ho harm was visable. I had misassumed that they were manufactured by simple insert-injection molding. Learn something new every day!

LED-FX-
Before I blow it again, 1000nm = 1 micron or micrometer. That would mean 280-400nm = .28-.40 microns. I think ordinary window glass is borosilicate. BK-7 was the only borosilicate glass listed and does poorly with UVC, getting better going towards A. And thanks for the link!

Larry