Mirrors versus diffuse reflection

[snikt]
> Plants do require one of the UV bands. You might see if you can find
> the spectral emission chart for a commercial plant light. I would
> expect that your standard white paint is a poor reflector of UV. I
> would also expect that a soft indirect glow would not work for plants.
> The leaf structure is in a plane perpendicular to sunlight. A leaf
> would have to be round to catch indirect sunlight. Pines have round
> needles but you need more than evergreens in a biosphere.
>

The leaf orientation problem, caused by phototropism (the tendency of plants
to grow in the direction of the light), is not exactly a problem, since even
my proposed diffuse lighting system would not provide omnidirectional
lighting: light would still come primarily from just one side and from
above - in fact, the polar cap glowing with indirect light would be
analogous to a white sun with enormous apparent diameter glowing in the
"sky" of the colony... At least in this case I have some experimental
(though far from scientifically rigorous) evidence: I have a plant in my
living room that never catches direct sunlight; even though, its leaves grow
in the general direction of the window - for most of the indirect light
hitting the plant is produced by sunlight hitting the walls and the floor
around that window. Therefore, plants inside the colony would still orient
their leaves toward the glowing cap and get some light input maximization by
doing so.

However, the UV need that you mentioned seems to be a problem. I was not
aware of it - as far as I knew, plants grow with any light in a relatively
broad band of the visible spectrum, peaking at red light... Even though,
maybe it is possible to produce a non-standard white paint that *is* a good
reflector also at the UV band that you mentioned - but I cannot say for
sure.

> Mitchell James

Lucio Coelho