Glass lens for custom dive torch

[Brettis87]

Hi guys,
I'm building a dive torch from scratch and am having trouble sourcing a lens thick enough. Im looking for something around the 70mm diameter and 5-6mm thickness range.
Can anyone point me in the right direction?

thanks,
Brett

 

[DIWdiver]

dealextreme.com and kaidomain.com both stock various sizes of glass and plastic lenses, most of which are not for diving. CPF member 350xfire stocks a couple sizes of borosilicate lenses (highly recommended, if they fit).
Also check this thread http://www.candlepowerforums.com/vb/showthread.php?292465-DIVE-LIGHTING-LIBRARY for additional references.

If you're just looking at one or a few, I can make polycarbonate lenses in any size/thickness that you can get material, with or without o-ring grooves. PM me if needed.

 

[Klem]

Hi guys,
I'm building a dive torch from scratch and am having trouble sourcing a lens thick enough. Im looking for something around the 70mm diameter and 5-6mm thickness range.
Can anyone point me in the right direction?

thanks,
Brett

I would use synthetic for anything greater than Maglite diameter. I tried normal 6mm glass for 100mm diameter a while back and it imploded at 19 Metres. Like in the movies...'Tick'(hairline fracture),... 'Tick' (another one), 'Boom' (flood)...darkness.

I source Perspex (6mm) from the local glaziers. Perspex comes fresh with protective paper on both sides that peels off. You draw a circle on the paper, then use a narrow blade on a jigsaw to carefully cut a circle to suit. Clean-up with a file.

 

[Brettis87]

Thanks for that info guys! I've been doing a bit more reading and have decided to go with acrylic/ Perspex. What is the light transmission of the Perspex like?

 

[Klem]

Perspex/Plexiglass has slightly better light transmission than polycabronate, although you'll struggle to perceive any difference with the naked eye. Perspex is likely to be a little cheaper.

Simple comparison here
http://www.hydrosight.com/technology/polycarbonate_vs_acrylic.php

Glass is the clearest, however with your diameter it would need to be thicker than 6mm to be sure.

Synthetic binds with glue nicely if you're going that way, but not very good with heat transmission. Be careful of it melting if it gets too close to point heat sources. Polycarbonate 'browns-out' if it gets too hot. Brown speckles appear, whereas Perspex melts like butter and goes opaque. I doubt you'll have any of those issues with LEDs. my experience with melting is from HID globes almost touching the lens.

For 70mm diameter 5-6mm Perspex will work fine.

 

[350xfire]

I was going to say that for 70mm I would probably use may be 8-10 mm... Unless, of course the lens is supported on multiple spots to minimize deflection due to pressure. I use 5mm on Mag builds and take them down to 265' without failures...

 

[DIWdiver]

I would use polycarbonate. It's much more resistant to fracture than acrylic.

 

[Klem]

What is the deepest you are likely to ever go with it?

 

[Brettis87]

The deepest it will most likely travel would be about 30 ish metres. Will have an O-ring to seal, rather than glue :-)

 

[Klem]

For that depth I would be comfortable with 5-6mm synthetic; either acrylic or polycarbonate.

O rings will work also.

 

[Brettis87]

Sounds like a plan! Any suppliers on the internet or should I just head to my local glazier / perspex dealer?

 

[Klem]

Every glazier should have the stuff. You might even get lucky and be given a small off-cut free.

You live in Perth...I use Balcatta Glass, opposite Bunnings, 188 balcatta Rd.

 

[bvanant]

I would use polycarbonate. It's much more resistant to fracture than acrylic.

Most big dome ports are either glass or acrylic since the optical properties of PC are not quite as nice as acrylic. At 7 mm thick it should be fine to 30 M.
Bill