Does IR LEDs melt PMMA optics like UV LEDs?

[Chatika_vas_Paus]

I need to make a lightweight IR thrower and am thinking of a C8 with smo reflector and MC13 manker which has great optics.

[skinny_tie]

I don’t really know for sure whether PMMA optics can be used with IR LEDs, but I was curious so I did a bit of searching. Hopefully if my comment is grossly oversimplified or inaccurate it will prompt someone more knowledgeable to jump in.

As far as I can tell PMMA doesn’t really absorb much IR light so I don’t think it would be melted by an IR LED. However, have no idea whether a TIR optic designed for visible light would produce a decent beam with IR.

There are lots of spectral transmission charts for PMMA online but this page from a manufacturer PMMA products is more my level:

@Poliedrica s.r.l

PMMA allows infrared light of up to 2800 nm wavelength to pass. IR of longer wavelengths, up to 25,000 nm, are essentially blocked. Special formulations of colored PMMA exist to allow specific IR wavelengths to pass while blocking visible light (for remote control or heat sensor applications, for example).

Source: https://www.poliedrica.net/pmma/?lang=en

The page quoted above also says that PMMA also transmits UV down to 300nm:

@Poliedrica s.r.l

Unlike glass, PMMA does not filter ultraviolet (UV) light. PMMA transmits UV light down to 300 nm. Some manufacturers add a coating to PMMA sheets to make them absorb UV light. PMMA molecules have great UV stability compared to polycarbonate.

I know polycarbonate absorbs UV - could it be that the optics that are melted by UV LEDs are actually polycarbonate rather than PMMA?

[alpg88]

i use pmma with ir leds, no issues, there may be losses vs no lens at all, but it works just fine for what i need it, i also use pmma with uv lower than 400nm, no lenses melted yet.

i’m not sure what gave you an idea it would melt,

[Chatika_vas_Paus]

Thank you skinny_tie for this information. I think I will try out other optics first to make sure everything is ok.

@alpg88

i’m not sure what gave you an idea it would melt,

Yajiamei optics are made of PMMA and it melts at 365nm. I’ve already checked it.

[alpg88]

@Chatika vas Paus

Thank you skinny_tie for this information. I think I will try out other optics first to make sure everything is ok.

@alpg88

i’m not sure what gave you an idea it would melt,

Yajiamei optics are made of PMMA and it melts at 365nm. I’ve already checked it.

maybe their optics is just bad, i never had any issues with ledil, and led engin optics with any leds at any power levels,

just do not use Yajiamei optics, there problem solved,

btw thanks for the heads up, i never heard of that brand, but now i’ll steer clear from it.

s. when you say you checked it, did you actually used it in a light and it melted?

[Chatika_vas_Paus]

Yajiamei optics are very well known in this forum and for white leds they are excellent.
And yes. I wanted to use the nichia 365nm from Simon’s store. After a while, I noticed that the beam had distorted.