Would putting a clear piece of protective film on the lens lower output?

Hey guys, I have some of this clear film protector that is made to protect the screen of the PSP .. and I was asking if I cut this out and put it in the front of the lens of my flashlight will it lower the output and if so by a lot? I know plastic lens are cheap but they don't shatter and I just have some of the protective film laying around and was wondering. Thank you.

I think a plastic lense can reduce the output of a light by as much as 20% but the film that you will be using is very thin so i doubt if you would loose much more than a few percent.

That film is used a lot to smooth the beam on Mags, etc. It does cut some output, but the smooth spot to flood seems worth it.

I have an Arc AAA turq that's really ringy. I warmed the head and stuck it on a piece of Writeright and trimmed it. It's been my around the house light for over a year and the film is still there.

I have done the same (made diffusers with a PSP screen protector). Cuts output by less than 5%, but cuts throw by about 10% (lux at hotspot by 20%).

Smooths the beam slightly - but not like the diffusion of a LDF UCL lens (which really hits throw)

I think a plastic lense can reduce the output of a light by as much as 20% but the film that you will be using is very thin so i doubt if you would loose much more than a few percent.

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The thickness of the medium isn't what causes the losses in most cases, it's the interfaces (where light enters, and exits the film) that do, due to the fact that a lot of the light is reflected rather than transmitted. Try shining your flashlight through your household windows and you'll see what I mean. This is why higher end flashlights, projectors, and camera lenses typically have anti-reflective coatings, and can achieve 99%+ transmission at selected wavelengths -- even huge TIR optics that can be very thick. Fiber optic cables can carry light for miles, absorption per unit length within the medium is almost negligible when talking about flashlight lenses.

The reason plastic can be so much worse for light transmission is that plastic is very prone to getting scratched, much more so than glass -- each scratch creates more interfaces, and more opportunity for light to be scattered/lost.

diffusion, reflection and transmission.
if you add a reflective surface, like a lens on top of a lens, some light will be bounced back.
plastic clean and perfect would reduce transmission by about 5% vrses uncoated glass at 8-10% , i am not sure how much of that is due to reflection.
diffusion, would change the beam pattern, but doesnt nessisrily reduce overall light output, depending on its trasmission and reflection .

there i bet that helps

Any film may alter the tint, also.

The clearer the film the better the output

OK for a plastic lens, but you didn't specify. If you are thinking of putting it on a glass lens to smooth out the beam, be careful about heat. If your light puts out a lot of heat that could be why it has a glass lens, and this film could melt (or worse).

Edit: Rereading your post, you do mention plastic but I'm not sure whether that is referring to the lens or the film.

yes. anything in the way will attenuate the beam to some degree.gc

If you want plastic which doesn't scratch as easily as the stock windows, check out the polycarbonate hardcoat lenses from flashlightlens.com.

I bought two of the one side hardcoat windows and cut them down (file) to fit in my maglite. They are a little thicker than stock so there's a small gap when you screw on the top ring but that's the only downfall.

Remember that a film may burn if the flashlight gets too hot. (Probably a bad idea to put one on a HID...)

in the spirit of a true CPFr I was going to answer this question for you as a gesture of good will and helpfulness. After reading the answers you got, I am now glad I kept my damn mouth shut.

After all, tis better to keep your mouth shut and have people THINK you are a fool than to open it and remove all doubt.

You received first class information and I saved face by not seeing your question first but my heart was in the right place.

Regards and welcome to the planet of CPF,

Vhyper007