You might see 0.1 FC in a 5 FC room through a 2% transmissive film.
I like Duraflex from Graphic Arts Systems in Cleveland. About 10 cents/ft^2 in 0.002"x54"x100' rolls.
Duane Johnson gets great results with Mylar heliostat mirrors.
Nick
So a lightwell lined with mirrors acts like a crab trap for entering rays. Rays enter, but they never come out. They are all passed downwards, with more reflections for rays from lower sky elevations and fewer for rays from higher elevations. But diffuse reflectors scatter light back up and out of the well. That seems like enough to convince most people that specular lightwells deliver more light, without any math...
I'm assuming that part is the same for the diffuse and specular lightwells, that indirect sun rays come equally from all over the sky hemisphere, and each point on a diffuse reflector reflects each ray out from its wall equally over its hemisphere, but a specular reflector beams each ray downwards with an angle of reflection that equals the angle of indicence. Always downwards, never upwards, because of the way rays enter a lightwell with parallel sides.
That might be nice at night. A specular lightwell with no diffuser at the bottom might have glare problems in direct sun. SunOptics makes skylights with lots of "microprisms" that spread direct sun about 30% more efficiently than white plastics with bubbles inside. They produce enough skylights every week (Wal-Mart is one of their customers) to offset 1 megawatt of peak electrical lighting power, without any government subsidies.
Nick
Yes, a 1892 row house in Brooklyn.
But the shaft is only a couple feet deep (the thickness of the roof). The amount of light that comes in would cost a fortune to replace with artificial. And the skylight is orginal, just I replaced the outside glass with an InsulaDome.
Don .
Well, there's my problem...I was thinking of my own that come down to a dropped ceiling in hall, etc.. Shafts are 6-8'.
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