radiation revisted

burkhard@aries.scs.uiuc.edu
Tue, 10 Dec 1996 12:19:27 -0600 (CST)

Hello list,

I would like to thank those who responded to my questions. However, I am
still unsure which lights would be the best for optimal growth. I agree
with Perry Malouf that these plants can be grown with artificial light
just as well as by natural sunlight. I believe that the intensity of
photosynthetically active radiation is the key. Say for instance, if the
PAR is in the 400-700 nm region (thanks Michael Chamberland), then I would
want a light with a greater intensity in this region. The question remains
is which radiation sources would provide the condition above.

Robert Pogson (thanks Robert for the input) pointed out that "radiation
rises with the fourth power of temperature". I would like to clarify that
it is the *total* energy density or emittance intensity, depending whether
you use Stefan's or Boltzmann's view, that is proportional to the fourth
power of temperature. Using these laws, one can only get information
dependent upon all wavelengths.

The maximum energy density at wavelengths of 700 nm for black bodies
requires temperatures that exceed 3800 degrees celsius and 6900 degrees
fahrenheit, based on calculations using Wien's Law. However, this is for
the maximum intensity of 700 nm radiation that a black body can produce,
which is far more than what is needed for the growing of plants.

I would be interested to know the experiences or thoughts on different
radiation sources from others on the list. Any other information would
also be welcomed. Also, has there been any experiments done with the
growing of plants using relatively narrow bandwidths of light (looking for
laser botanists)?

Paul Burkhardt