From: macrakis@osf.org (Stavros Macrakis)
Subject: Re: Plant lights
Date: 25 Mar 92 10:19:26 GMT

callahan@biffvm.cs.jhu.edu (Paul Callahan) writes:
   ...can somebody tell me what makes a plant light different from a
   normal light.

The spectrum.

   ... it makes... sense to add some (especially in the UV range) in
   order to mimic sunlight.

The big difference between indoor lighting and sunlight is the
intensity.  Plant lights concentrate their energy in bands where
plants need it, so the visible intensity is proportionately less.
Plants actually need a lot of red, and not so much UV.  By far the
most reasonable way to provide this is the special fluorescent bulbs.
There are two kinds, both of which are fine for the plants, but one
makes them look an ugly color.  `Grow and Show' bulbs produce a
reasonably nice color.  Fixtures are cheap.  Incandescent bulbs are
very inefficient, and produce amounts of heat that can hurt the
plants.  With fluorescents, you can place the bulbs a few inches away,
concentrating the light where it's needed.  For larger applications
(greenhouses), high intensity discharge lamps are a better solution.

   Is the filament made of a different material than regular bulbs?  

Incandescent bulbs put out a black-body spectrum (which doesn't
correspond to plants' needs particularly well).  Only temperature, not
material is relevant to the color.  Halogen filaments run hotter and
therefore bluer.  (But blue light is called `cooler' than red
light...)

	-s