"Glen Able" wrote in message
...
OK, imagine an torch pointing straight down onto your work surface. (Or
do
it with a real one!) Now imagine it tilted at an angle - it's obvious
that
the same amount of light is spread out over a much greater area of the
surface. Likewise there is less light energy per unit of surface area
when
the sun's lower in the sky.

As Kay points out, there's also the effect that when the sun is lower in
the
sky, the light has to travel through more atmosphere is and gets
dissipated
by this. So you can't use an angled mirror at sunset to get the effect of
noon at the equator!


I did mention both those points in my original question.

I still think the mirror has some benefit though - because the area of the
mirror is greater than the area of the greehouse floor, it's getting more
light into the greenhouse. I've drawn a diagram here :
http://www.users.globalnet.co.uk/~sy...reenhouses.jpg

In the standard greenhouse, some light just passes through without going
near the plants. In the modified one on the right, the roof is asymetrical
and internally mirrored on the side away from the sun so that that light
gets redirected to the plants. I bet it wouldn't be an expensive
modification and might make more of the little light we have. You could also
mirror the vertical side as well. Maybe even tin-foil would do the job?




--
Martin & Anna Sykes
( Remove x's when replying )
http://www.users.globalnet.co.uk/~sykesm