I have metal halide fixtures that have a clear glass. I would like to
make some sort of a light diffucing glass and am curious if there are
any paints or coatings that stick to glass and are white and diffise
Something like chalk paste or some such (which I can make myself in a
blender if it is suitable).
You have to be very careful - even clear glass gets quite hot in such a
fixture and by changing the glass you probably have to re-do UL
That said, the keyword you want for diffusion in such a fixture is
"frosted" or "prismatic". Glass remains clear but is cast (prismatic)
or sandblasted (frosted) in such a pattern that internal
reflection/refraction takes care of diffusion.
If you want a reflective white diffusing coating, the standard optical
product is called "Munsell White Reflectance Coating". It's real good
stuff and easily coated onto glass. I suspect you're talking about a
transmissive diffuser, though (the other side of a piece of glass
coated with this stuff will have only a tiny fraction of a percent of
light shining through!)
And a colleague who used to work in the lighting industry informed me
that most frosted glass used to be done with hydrofluoric acid etching,
although he was of the opinion that this is seen as environmentally
You know, if you and I lived a bit closer, I could see us hanging out
together regularly. I've got a blast cabinet in the garage...
One thing to think of - around here we have an outfit called "U-Spray"
which rents sandblast cabinet time by the minute. Inexpensive, they
have all the equipment, and you just pay a flat fee based on your time.
Might be a franchise?
At least from my own experience with MH fixtures, there's a good
chance the glass is tempered, designed to protect you from excess UV
and from showers of nearly-molten quartz if a bulb ever detonates. I
would not mess with the factory glass.
How hot does the outside of the glass get?
I used to have an MH in my garage that was a high-bay fixture in a
lower-height room, so I put an external diffuser on it, just cut a
circle out of one of those plastic diffuser sheets you can get at the
hardware store for 4-tube fluorescent fixtures, and mounted the
circle an inch below the MH fixture's glass.
firstname.lastname@example.org is Joshua Putnam
When I wanted frosted glass in an outdoor lamp fixture I frosted it with a
palm sander and aluminum oxide paper (I think.) it was a long time ago.
Maybe emery paper. I would think 80 grit would be about right.
Add a piece of frosted glass.
Frosting your glass can weaken it and MH fixtures need a sheild in case
of "non-passive failure."
There are some theatrical materials that come in a wide range of
frostings and colors. If the heat isn't too great they would be ideal.
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