I've lost count of how many times on these newsgroups I've encountered
someone saying that providing space habitats with natural sunlight via
mirrors and windows would just be too complicated, and we'll instead use
artificial illumination. Sometimes the advantages of using red LEDs to
raise crops are touted (less wattage, less need for heat rejection).

I've always argued against this, mostly from instinct, but also from knowing
the actual solution the original space settlement studies did settle on. I
was concerned about conversion efficiencies (why convert light to
electricity and then back to light again when light is what you wanted in
the first place?), and it always struck me that aluminized Mylar and glass
panels by the square mile would be pricey, but PV arrays and artificial
lights by the same magnitude would be more so.

Here's a paper that seems to agree:

"Effect of Environmental Parameters on Habitat Structural Weight and Cost"
http://www.nas.nasa.gov/About/Educat...eres/II-1.html

In the midst of looking into a variety of parameters for habitats for 1,000
(early construction shack), 100,000 (intermediate range earthlike habitat),
and 10,000,000 (long range habitat), and for toroidal, spherical,
cylindrical, and Crystal Palace geometries, the paper compares the costs for
artificial vs. natural illumination.

Table 6 indicates that natural illumination with mirrors should have only
about 20% the cost of the artificial illumination option.

The paper does agree that concentrating solar energy so as to minimize
window area is to be recommended. They say you could get up to a solar
concentration level of 70x before getting into problems with the glass
softening.

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Regards,
Mike Combs
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By all that you hold dear on this good Earth
I bid you stand, Men of the West!
Aragorn