DIY MH Pendant Glass Thickness, Composition

[altisimus]

I'm currently building a 24"x18"x8" light pendant using a PFO combo reflector, 1x 175watt SE MH and 2x 65watt PC. My current thought for the protective glass would be a piece of 1/4" thick tempered for durability and assumed resistance to breakage from water splash while hot (the pendant is vented on one side with a fan pulling air through the reflector to the other). At that thickness, I'm curious if the light dispersion/refraction would have a significant effect on PAR measurements, and if low-iron glass would be a better option with respect to available light. The tank inhabitants are primarily mussids, faviids, and mondtiporas, although the option to keep corals with higher light requirements in the future would be nice. Any opinions/suggestions would be welcome!

[Clownfish518]

With the mogul bulbs you don't need glass for UV protection. Most folks (myself included) run moguls without glass.

DE (HQI) bulbs you need glass. You have to have them high enough off the water anyway; I never get splashes that high

[altisimus]

Good points; In the fixture I'm building the mogul bulb is situated 4" higher than the two PC bulbs, so while it may be safely out of splash range at 8"- 10" above the water the PC bulbs will be 4"- 6". Currently at that height the bulbs get a salt spray coating and I've replaced two sockets due to corrosion. For me, the glass is necessary.

[Clownfish518]

Huh. 6" above the water I would not expect splashing. Do you have a filter or something kicking the water up?

The glass will cut down a good 30% or so of the light from reaching the tank. Low iron light will allow more light through. Try to keep it as thin as possible is my advice

[altisimus]

I have much surface agitation from two 1" returns coming from an upstream fuge, more of a salt spray than splashing. 30% ? Wow, wouldn't have guessed that much. Thanks for the number, it's a big help.