How to tell a glass from a plastic lens

I know this is probably a ridiculously simple question, but I've never let that stop me. What is the easiest way to tell if a lens is glass vs. plastic? I have a couple of lights where it is difficult for me to know for sure. I remember a post from long ago that mentioned an easy way to tell---something about holding the lens at a certain angle---but I can't find it now.

Thanks for any answers.

When you look at the glass from the side it will have a green tint to it. (That's IF it is glass) A plastic lens will have a clear, whitish appearance.

Another way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.

Hit it with a hammer and see if it breaks.

Or do the teeth thing. That's what I do.

xiaowenzu said:

Another way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.

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Whew! So I'm not alone on this one.

xiaowenzu said:

When you look at the glass from the side it will have a green tint to it. (That's IF it is glass) A plastic lens will have a clear, whitish appearance.

Another way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.

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It will only have the green or purple tint if it is antireflective coated. One that isnt coated will be "white" as well. Plastic can be antireflective coated too, so looks aren't a reliable way of checking.

I tap my fingernail on the lens and that clearly tells me if its glass or plastic. The glass feels alot more solid and the sound is like a soft tapping where the plastic sounds like a thumping and is alot louder. It's a big difference and theres no mistaking it.

the tooth-sensor works best.

BigBaller said:

I tap my fingernail on the lens and that clearly tells me if its glass or plastic. The glass feels alot more solid and the sound is like a soft tapping where the plastic sounds like a thumping and is alot louder. It's a big difference and theres no mistaking it.

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That worked fairly well for me too, until I tried it on my Streamlight ProPolymer 4AA. The plastic they use in that is very hard and has an almost glass sound to it.

You could just flick the lens, if it gives a solid pingy sound then it's glass if it's a low blop type sound it's plastic. It's like when you flick crystal glassware.

i guess there r different grades of plastic / glass. i swapped the original Pelican M6 2390 plastic lense w/ another photographic quality lense. & i can really see the difference between both plastics.

any1 popped a saphire crystal lense from a watch for your flashlight?

i guess there r different grades of plastic / glass. i swapped the original Pelican M6 2390 plastic lense w/ another photographic quality lense. & i can really see the difference between both plastics. plastics is fine w/ me.

any1 popped a saphire crystal lense from a watch for your flashlight?

xiaowenzu said:

WAnother way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.

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If you do it right, it will break your tooth if it is glass and it will bounce back if it is plastic :laughing:

The window-lens in front of my Thor 15MCP knock-off is supposed to be glass, but tapping it it's hard to tell. I think it MUST be glass, because plastic probably would melt!

I use my fingernail first. If I can't tell, I just tap the lense with the edge of a penny. I can always tell using the penny-tap test.

Another vote for the 'tooth tap'.

Cliff

Thanks, guys, for the tips.

the tooth tap woked for my u2 and a2 but i can not tell if my 8nx is or not does inyone know?

Before tooth tap test

After tooth tap test


TIP: Remove strike bezel before testing. :laughing: :lolsign:

benchmade_boy said:

the tooth tap woked for my u2 and a2 but i can not tell if my 8nx is or not does inyone know?

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I have the 8AX and the 8NX, the AX lens is definitely, and obviously glass, but the NX lens, being surrounded by plastic, doesn't sound as 'glassy' when tapped. Attempts to (gently) scratch it with a knife tip proves it is glass, at least on mine, late model I think, earlier ones may be lexan.

RAF_Groundcrew said:

I have the 8AX and the 8NX, the AX lens is definitely, and obviously glass, but the NX lens, being surrounded by plastic, doesn't sound as 'glassy' when tapped. Attempts to (gently) scratch it with a knife tip proves it is glass, at least on mine, late model I think, earlier ones may be lexan.

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Thanks! I am pretty sure mine is pyrex becuase i compared tooth tap to my g2 and there is defenitly a differnce but i canot decide if i have the old 8nx or the new 8nx cuz my box was very old but my green charger light stays constant on then about an hour after that it startes blinking.

sorry for getting so of topic