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The end is near.....glass or plexi?
RandyT:
--- Quote from: versapak on November 04, 2004, 11:15:50 am ---
--- Quote ---Also I assume that tinted glass will cut down on reflections?
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I would think that it would actually make it worse. The darker it is the more mirror like it would be.
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Ras2a gets the nod on this one. Read on to understand why this is true.
Glass and other optical materials have a number of properties; Diffusion, Surface quality, distortion, reflectivity, transmission, absorption and index of refraction to name a few. These can all be controlled to a certain extent by manufacturing processes and/or optical coatings.
The ones that we are concerned with the most are Transmission, Reflectivity, and to a lesser extent, absorption.
The reflectivity of a surface is pretty much a constant based on a material and it's finish. You perceive the darker material to be more reflective because less *transmitted* light gets mixed with the *reflected* light and the reflected light is seen with less interference and is therefore seen more clearly.
A simple way to think about this for our purposes is:
% Transmission = 100 - (% Reflectance + % Absorption)
% Absorption = 100 - (% Reflectance + % Transmission)
% Reflectance = 100 - (% Absorption + % Transmission)
So in plain English, the less a material transmits and absorbs, the more it reflects, and the less it reflects or absorbs, the more it transmits.
Regular *clear* window glass, has a reflectance of about 2% per surface, or 4%. If that same glass were opaque (i.e. 0% transmission in the visible spectrum and essentially black to the human eye) then you could only get a reflection from one surface. Therefore, a dark piece of optical material is actually *less* reflective than a clear piece.
So what is optimal?
Something very expensive. If you can afford it, an AR coating (Anti-Reflective) would be essential. The material itself should absorb light *evenly* across the visible band. This is known as a Neutral Density Filter. The percentage of light that is allowed to pass should start at about 32 and go down from there, depending entirely on the effect you desire.
But what is practical?
Something that does the job, without breaking the bank. If you are looking at a very specific transmission, clear glass with a well-applied window tint may be what you want. Plexi comes in a "light" and "dark" version. It is also made by a few companies under different names, but it's all Acrylic plastic. Most will have their own light and dark versions, but may differ by the color and how much light is transmitted.
Suggestion.
Get samples! If you can get a small chunk, take it home and see what it does over your screen. When you get what you want, buy a bigger piece.
But if you want to hide your screen, 20% or less (the dark smoke acrylic is usually between 16% and 18%) If that's not what you are after, try 30% or slightly above. You may need to go with one type of material over another just to get the specs you are looking for, and there's always automotive tint as a last resort.
...and that's about all I can tell you.
RandyT
darktemp:
I've found that some shops carry 1 type of smoked gray glass which they call "regular gray" (not real helpful), however some shops carry the regular gray along with "graylite". At first I would have assumed that the graylite was a lighter gray and wouldn't work, after doing some research however I found this:
"Graylite is unique among all tinted glass, offering a dark-gray, almost black appearance which provides excellent glare control, shading coefficient and ultraviolet screening. Available in two thicknesses:
Graylite #31 (31% light transmittance) is 1/8" thick
Graylite #14 (14% light transmittance) is 1/4" thick "
I had been calling around looking for a tint with a light transmittance around 20% as RandyT suggested but nobody had that information. So I ask, is 1/4" graylite at 14% VLT the best glass to use or is it too dark?
ras2a:
Wow, thanks for that Randy, you sound like a clever bloke who knows his stuff. Nice one mate :). Also Darktemp, thanks for that...never heard of greylite before. I have been told that you can get laminated glass and it's the laminate part that is tinted rather than the actual glass itself. This sounds like a feasible option, but again, it's knowing what to use. I think I'll just experiment a bit as Randy says, until I find summat that works for me.
thanks guys!
keltech:
--- Quote from: Minwah on October 21, 2004, 10:38:40 am ---Another vote for glass here: I got a piece 599x642mm, tinted & toughened for
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Minwah:
--- Quote from: keltech on November 15, 2004, 05:56:41 am ---I was just wondering where you got your glass cut cheap in the UK? have you any contact details please
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I got mine from this place:
Witney Glass
Unit 1,
West End Industrial Estate,
Witney,
OX28 1UB
01993 771515
I know they don't do the cutting/tinting/toughening process themselves, they send it somewhere. One thing I would say is that they cut it very accurately, from the measurements I gave them.
You might end up paying more with shipping costs etc. tho. Personally I would probably prefer to get glass locally...