Seeking opinions on best material:

[Jeff Engel]

The premise:
When sunlight enters the space through a window or skylight, it brings
not only light energy but also heat energy. Except in cold climates,
this solar heat gain from daylight can be a burden on the building
cooling system, and sunlight must be carefully controlled to avoid this.

But with good design, the daylight is not only a good source of light
but the most efficient. The number of lumens per watt (efficacy) of
daylight is twice that of a fluorescent lamp and ten times that of an
incandescent lamp. Properly designed daylighting strategies can both
reduce electric energy demand for lighting and minimize loads on the
cooling equipment.
Our subject: What material or method will pass or reflect most light
and reflect or absorb most heat? Anything more practical to be done
with the waste heat? Are those efficacy claims above valid? Is this
more interesting than LED holiday lights?

 

[TKM]

The premise:
When sunlight enters the space through a window or skylight, it brings
not only light energy but also heat energy. Except in cold climates,
this solar heat gain from daylight can be a burden on the building
cooling system, and sunlight must be carefully controlled to avoid this.

But with good design, the daylight is not only a good source of light
but the most efficient. The number of lumens per watt (efficacy) of
daylight is twice that of a fluorescent lamp and ten times that of an
incandescent lamp. Properly designed daylighting strategies can both
reduce electric energy demand for lighting and minimize loads on the
cooling equipment.
Our subject: What material or method will pass or reflect most light
and reflect or absorb most heat? Anything more practical to be done
with the waste heat? Are those efficacy claims above valid? Is this
more interesting than LED holiday lights?

No doubt about it; daylighting is a good thing especially when the new
research about light and hluman health is factored in. Boiled down, it
leads to the conclusion that humans need bright days and dark nights.
Electric lighting can't easily meet the "bright days" criterion -- too much
energy use, cost and heat result if the high lighting levels required are
put into work spaces. But daylighting is a good solution for most climates.

The last time I checked, sunlight came in at 120 lumens/watt and "low E"
glass was a great way to handle the radiant heat; but I'm not an expert.

Terry McGowan

 

[David Lee]

TKM wrote...

No doubt about it; daylighting is a good thing especially when the new
research about light and hluman health is factored in. Boiled down, it
leads to the conclusion that humans need bright days and dark nights.
Electric lighting can't easily meet the "bright days" criterion -- too much
energy use, cost and heat result if the high lighting levels required are
put into work spaces. But daylighting is a good solution for most climates.

The last time I checked, sunlight came in at 120 lumens/watt and "low E"
glass was a great way to handle the radiant heat; but I'm not an expert.

Terry McGowan

I was very impressed at the daytime-lighting installed in the kitchen area
of the Worcestershire Wildlife Trust headquarters (UK). The kitchen was
built onto the back of an existing barn and has a turf roof running down to
ground level and so has no natural light. Prisms on the roof collect
sunlight and pipe it down to light fittings in the ceiling. It's extremely
bright and of course zero cost in energy to run.

David