Stephen Henning wrote:
John Thomas wrote:


For what it's worth, Scientific American had an amateur scientist column
c. 1969, since reprinted in collection of the columns, on what sort of
lights work best with seedlings and mature plants.


I have been taught by the experts that the "gro-lites" are a waste of
money. The best grow lights are a mixture of cool white and warm white
fluorescent tubes. On a 2 tube fixture, use one of each. On a 4 tube
fixture, alternate with 2 of each. This combination the highest lumens
per watt and spans the optical spectrum best.


That information was correct 30 years ago. The EPA ruined 40W
fluorescent cool-white and warm-white lamps back in 1974, IIRC. But
even back in the 70's, cool-white and warm-white lamps did not maintain
their luminocity very well, and you had to change the lamps every year
or two to get good plant growth with them.

If you want good lighting today, you use GE SPX series lamps, or Philips
or Osram "ALTO" 800 series lamps. The lamps are cheap, they have a very
good spectrum, and they maintain typically 90% of their luminence for
20000+ hours.

Regards,
Bob