Dr. Rev. Chuck, M.D. P.A. wrote:

Andrew Ostrander wrote:

I don't think a double bank would be adequate, but a ceiling covered with
fluorescents would be enough for some plants at some stages of their growth.
It would be prohibitively expensive for commercial greenhouses to do that;
sunlight is free.

Andrew


Don't they supplement with halides when daylight hours are short?


They use incandescent lamps in greenhouses if they are just trying to
lengthen the hours of daylight for plants that are sensitive to day length,
because incandescents are cheap and they don't need much brightness. They
use high pressuse sodium lamps if they need to supplement the amount of
light. The natural light provides plenty of blue wavelengths to regulate
plant growth, and HPS are more efficient and have better lumen maintenance
than metal halide lamps. (that means they don't start dimming out after a
few hundred hours.)

Best regards,
Bob