The ASNSW in ther light use policy document for the Wiruna Dark site advise
Quote:
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Filters should be made from a deep red gel filter material, which can be obtained from theatrical lighting suppliers such as Herkes Electrical Supplies Pty Ltd, 890 Bourke Street, Waterloo (Tel: 02 9319 3133)
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Quoted from
http://www.asnsw.com/wiruna/lightusage.asp
I have spoken with Herkes and they have this filter. I recall when I looked there address up they are not far from the Bintel shop in Sydney.
I have also seen on Amart a product sold called Rubylith, which apparently is equivalent of 25a Red photographic filter.
It is sold by these guys on Amart
http://www.astro-rubylith.com/Home.html
Also have read that this maybe available from Art supply stores, but i have not looked there. But do not confuse it with Red Acetate which could be used but is not as good.
There is also a Article on IIS about using Neutral Density filter material instead of the Red filter. To cut the brightness of Laptop screens.
Regards
Fahim