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re: best reflective surface for skylight shaft?
1 aug 2004
dadioh wrote:
>nicksanspam@ece.villanova.edu wrote:
>
>> specular reflectors pass these rays downwards with little intensity
>> loss. diffuse reflectors scatter the light all over the place--
>> down, up, and horizontally to adjacent walls...
>
>agreed.
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...
>but the difficulty would be to get the specular reflectors to collect the
>light from source and direct it to where desired.
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.
>...if i were the op and wanted to light a stained glass window in the
>ceiling i probably would have scrapped the skylight in favor of artificial,
>controllable light.
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
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