Flashlight lenses, how to tell them apart?

How can you tell the difference between a pyrex lens and a lexan lens, or other varieties? Like on my M2 ?

Tapping the lens will tell the difference between lexan and pyrex. Pyrex will sound like glass and lexan sounds plastic.

Geoff

Maybe there is someone with more knowledge than me, but . . .

Pyrex is glass and Lexan is plastic, so, taping lightly on the lens with a metal pbject, glass sound like "klink klink klink", whereas plastic has a deader "tap tap tap" sound.

To set a reference point before doing this on your lens, tap the metal object on a known glass and a known plastic object to get familiar with the sound.

As with BuddTX's tapping suggestion, tap your monitor screen (you should all be sitting infront of it! /ubbthreads/images/graemlins/smile.gif) that's the sound of glass.

Actually, tapping doesn't sort out the difference. I tried it on a UCL in my TL, it doesn't have the resonance of other glass, possibly due to the small size of glass and it being tightly screwed down against o-rings.

Mine isn't. /ubbthreads/images/graemlins/grin.gif
(You knew someone would say it).
LCD.
I guess if I tap real hard I could break the glass substrate...

the M2 should be Pyrex. Surefire will glue pyrex lens to the the bezel, Lexan is snapped in and held together with an o-ring.

FC might provide examples.

Geoff

Tap with a metal point - Glass sounds like tapping glass, plastic sounds like plastic.

Al

Nup Size15, I tried it with my folding knife. UCL in TL vs PT Surge. The Surge sounded more glass than the UCL did.

I am not suggesting that anyone try this, but on the Mohs Scale of Hardness, Glass rates 6-7. A knife blade is 5.5. With that logic, a knife will not scratch a pyrex lens, but it WILL scratch a plastic (lexan) lens. Personally, I wouldn't try this experiment on my beloved lights, but if you really want to know.....

(I'd sooner contact the manufacturer!)

If you look at a reflection in pyrex it will look nice and sharp. With the lexan lens the reflection will appear a little distorted! (must be sober for this test!)

kev's suggestion is the best. the lexan will usually be a little warped due to the tension from the snap-fit. on surefires at least, the reflection on the glass lens will also be dimmer due to the anti-reflective coating.

Interesting thoughts here.... I'm obviously assuming you can't get the lens out, which means it's probably either press-fit poly or glued glass. Most polycarb lenses I've seen on lights have practically come from the factory with a few scratches. In fact, I haven't met a poly lens I couldn't put scratches in with a rough piece of skin on my finger.

A test? - If non-destructive tests aren't telling the tale, then I'd suggest using a pin. Give the lens a little rub with the point near the edge. You should quickly be able to see the result. If you use a dental pick type instrument, you may even hear the result - a glass lens might cause the pick to resonate and squeak a little.

flashlightlens: sometimes when cleaning the lens on my C2 with my t-shirt, i put what i think are scratches on it which can't be cleaned off. but when i use a proper liquid cleaner on it, the scratches come right off. this is probably because lexan gets stained easily, and stains on a lexan lens are harder to clean off than on a glass lens.

My wife, who beads necklaces etc., taps beads against her front teeth to tell glass ones from plastic. Works well, and they make quite a different bone conducted sound, as well as a different tactile sensation on the teeth.