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re: best reflective surface for skylight shaft?
31 jul 2004
dadioh wrote:
>>> ...max reflectance may not give you the max output at the bottom because
>>> they are so directional.
>>
>> not according to the usual lightwell calculations.
>>
>>> ...a non specular (not glossy) white or aluminum paint would probably be
>>> best due to the usual shape of a skylight shaft.
>>
>> i doubt that. can you find a specific example that makes your claim true?
>
>can you line a skylight chase with mirrors (or even specular reflectors) so
>they reflect the skylight opening to the ceiling opening?
think "non-imaging." direct sun aside, the question is: "can a lightwell
with diffuse reflective walls move more lumens into a room than one with
specular walls, given a skylight that collects a certain solid angle of
diffuse isotropic sun?"
intuitively, light rays enter the skylight from all directions. if the
lightwell is vertical, vertical rays from overhead sky pass all the way
down the well with no reflections in either case, like shining a laser
down a pipe. slightly off-vertical rays are reflected from the walls far
down in the lightwell. more tilted rays hit the walls nearer the top.
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...
we could make this more mathematical, if you like.
nick
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