"J. Del Col" wrote in message
The best way is to use a light meter calibrated in footcandles.
Good ones aren't cheap.

Are these too cheap to be good?
http://dansgardenshop.com/liginmet.html $27.95
http://greenhousestuff.com/instruments/lightmeter.htm $29.95
http://www.greenfire.net/hot/E611.html $24.95

But even if they are not very accurate, could they be "accurate enough" for
the purpose of establishing whether the light is good enough?

I am also thinking of getting a light meter. I grow my Phals in only
northern windows with some supplementary grow lights. I know that the window
without the light is not enough because the first year that I had two Phals,
they did not rebloom and one of them keiki'ed, and the new leaves were too
dark. So then I got the lights. The main thing I keep wondering is, how far
from the grow light can I put my Phals -- being an orchid addict I keep
buying more, of course, and not all of them can be equally close to the
lights and windows -- I can get more lights, but I would like to know if it
is needed. I would rather not wait too long -- I don't want to risk the next
blooming season for those orchids that currently might be too far from the
lights.

Joanna