Visit the URL below for a nice writeup. I copied this paragraph from the
page.

It is important to select artificial lighting that provides both ends of
the spectrum in sufficient intensity. Household
incandescent bulbs are very heavy on the red end, while cool white
fluorescents are weak in reds and strong in the
blue end. That's why 50/50 wattages of each can be combined for
successful growing. Recent developments in
fluorescent phosphors have yielded spectra more like natural sunlight by
boosting the red end of their light output.

http://www.firstrays.com/plants_and_light.htm

Hal


Bette Noir wrote:

Hello, all,

I just got some light fixtures to supplement the light for my orchids
that are in a west window. At Home Depot I was sold some lights that
they said were wide spectrum. Well, the guy didn't seem to understand
what I wanted, after all. They are apparently considered intermediate
spectrum: the color temp is 3500k.

This seems to be pretty close to the temp for bulbs rated as warm. If
I mix two of the 3500k bulbs with bulbs that are rated cool, will I
have enough of the spectrum covered? Or do I need to ditch the 3500k
for 3000k? This seems to be a bit hard: there don't seem to be any
"warm" T8 bulbs on the shelves.