Re: Radiation

ROBERT POGSON (robert.pogson@mwcs.mb.ca)
Sun, 08 Dec 96 11:13:00 -0600

CC> From: burkhard@aries.scs.uiuc.edu
C> Hello all,
C>
C> One of the concerns that a plant grower has is lighting. We are all aware
C> that usually plants do better with natural sunlight than with artificial
C> light. A reasonable explaination for this is sunlight provides a wide
C> spectrum of frequencies. However, ideal "black body" radiation provides
C> all frequencies of radiation. The heating of a ceramic rod closely
C> simulates the frequency output of such a black body and therefore
C> analagous to an ordinary tungsten incandescent light. Yet, most "grow"
C> lights are flourescent.
The spectrum of black body radiation shifts with temperature. The sun
is hot enough to give plenty of light in the visible range while a hot oven
produces mostly in the infrared range. The fluorescent lights are simply
more efficient than heat at producing visible light because they use
electronic excitation of atoms to produce ultraviolet and fluorescence to
shift energy to the visible range.

C> I am currently using halogen lights in place of incandescents, but have
C> not seen any dramatic improvements other than in my electric bill.
The halogen lamps are just a variation of the incandescent using a
halogen gas to permit higher operating temperatures without much evaporation.
They should produce more light with the same energy consumption, because
radiation rises with the 4th power of temperature.
C>
C> If anyone could provide any information on the frequencies of light that
C> plants utilize the most, I would most appreciate it. I am under the
C> impression that it must be in the ultraviolet region.
Chlorophyll is green so it probably uses something other than green for
photosynthesis. The process is organic, so it is probably not a resonant
absorption like ionization. Has anyone tried sodium vapour lighting? It is
a very pure orange and about as efficient as electric light can get because
the sodium is easy to ionize and no wavelength shifting is necessary. Plants
look putrid under it, however. You could use one source for growth and
another for viewing...

C> Paul Burkhardt
C

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