Torch Light lens material.

[wen gege]

Hi there, i would much appreciate if anyone can advice me with my doubt.
I have a DIY canister dive torch light, the frame is make of alluminium, lens is arcylic.
I would like to know will my lens crack underwater due to pressure of 40M if it's arcylic?

Thanks in advance

 

[Packhorse]

That would all depend on the thickness of the lens and its unsupported diameter.


I use 3.6mm acrylic at 50mm diameter down to 57 meters and have had no issues.

I used a stock polycarbonate maglite lens to 42 meters before it went concave and pressed so hard against a MR16 bulb that it smashed it. Then lens was fine though and the light didnt leak.

 

[wen gege]

alright. i am just worried it will crack. will tested it out on wed night dive.

 

[DIWdiver]

I posted a calculation of this a little while ago. Search my posts or PM me if you are interested.

Acrylic is slightly stronger than polycarbonate (yeild strength is 100 KSI as opposed to 90 for PC), but much more prone to cracking - the number I've heard is 7 times. Glass is stronger still, but we all know how prone it is to catastrophic failure! Borosilicate glass (pyrex is one brand) is much tougher than other glasses, but is less common. Since I typically want to machine an o-ring groove in the lens, I have to stick with plastic.

Thus my choice is PC. If I could get borosilicate glass in exactly the right shape, I'd prefer that.

Keep in mind that the lens can absorb anywhere from 1-10% or your light output when new, and wear makes this worse. If I was going for the record books on brightness, I'd go with ultraclear glass (99% transmission).

D

 

[wen gege]

Got my DIY canister underwater on the 15/07/09. outcome was good. didnt i expect to it to be strong.

my torch light lens is make of arcylic, so far it did not crack underwater of depth of 16.8m.
Thanks to all who advice and guide me along. will post a few photo soon

 

[Packhorse]

How thick is it and what diameter?

 

[wen gege]

How thick is it and what diameter?

If i remember correctly, i am using a 3mm thinkness len.
however, i also use RTV underwater silecone to seal the len edge of the torchlight just to prevent it leak. Though of using glass, but i think glass is weaker than arcylic.