# Lighting fixture terms?



## derekleffew (Oct 31, 2009)

What do the words borosilicate and phenolic mean, relative to lighting fixtures?


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## epimetheus (Oct 31, 2009)

Well, before I go looking up the answers...

Phenolic is a plastic-like substance that was widely used as an electrical insulator (maybe not in theatrical lights) in the years of past. It was and is often used as a material for handles and knobs, which is where I think it is usually found in theatrical lighting, as is doesn't transfer heat very well. This means that the handle or knob will not heat up as much as a metal one when a fixture is hot. The problem is that over time, when constantly exposed to heat, phenolic can break down and become brittle. This is the main reason it not as widely used as an electrical insulator anymore.

Borosilicate I think has something to do with lenses, but I'm not entirely sure without looking it up.


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## tjrobb (Oct 31, 2009)

Borosilicate is a type of glass (boron + silicon, maybe?), and is heat-resistant IIRC, but beyond that I can't remember. As for phenolic, what was already stated is the limit of what I know.


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## calkew5 (Oct 31, 2009)

The Source Four reflector is borosilicate, right?


> Faceted borosilicate reflector with dichroic cold mirror coating
> removes greater than 90% infrared radiation (heat) and
> reflects greater than 95% of visible light



Of course, this doesn't mean I know what it is.


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## photoatdv (Oct 31, 2009)

Okay... my guess is borosilicate is a type of glass (maybe B(SOv3)v3 looking at a periodic table) Glass is formed when there's a random arrangement of particles... so it could be that stuff cooled really quickly . We made glass using I *think* boron and something in chemistry class last year.

As for Phenolic-- I know phenothalien (sp?) is an indicator. Well I found phenol in my chem book... so most likely it is an plastic that has phenol groups in it.


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## shiben (Oct 31, 2009)

My guess is that borosilicate is used for all the optics of the source 4. Its used in all kinds of high heat applications, due to the fact that is has a very low thermal expansion, allowing it to resist thermal shock, as well as maintaining optical clarity even at high heat. 

As for Phenolic, Bakelite is made from Phenolic Resin, and for a long time Bakelite was pretty much what insulators were made of. I believe that its no longer used much because its hard to make or something like that. However, Im fairly sure that a ton of old lighting instrument parts were made from the stuff, including the plugs (some of ours still have Bakelite plugs), knobs, etc. I would imagine nowdays that they might have switched to ABS or something else, but it is still in use, so maybe not.


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