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Finding the optimum wavelength of light for the best plant growth

john markwell markwell at unlinfo.unl.edu
Mon Apr 18 07:55:31 EST 1994

j-cheeseman at uiuc.edu (John Cheeseman) writes:

>Despite the fact that chlorophyll absorbs maximally in the blue and red,
>photosynthesis (and thus growth) is almost equally efficient across the
>entire visible spectrum from 400 to 700 nm.  Therefore, sunlight is good
>stuff, tungsten would be good except for the large heat load if you are
>using it in a closed area, and the fact that the heat load represents watts
>you are paying for without results.  Fluorescents, halides, mixed halides
>and all those give usable light, depending on what your specific plant
>requirements are and you budget.  

The above statement about all wavelengths being almost equally 
efficient is both correct and incorrect.  If one considers the quantum
yield, then any visible photon which is absorbed is effective (+/- 
25%) at driving photosynthesis.  However, if one desires to examine 
the efficiency of different light sources, then the action spectrum 
must be considered.  The blue and red photons are absorbed with a high
molar absorptivity, whereas the green and far red are not.  The 
wavelengths which are not absorbed do not drive photosynthesis to any 
appreciable extent.  To get information on the quantum yield, you 
might consult Emerson and Lewis (1943) Amer. J. Bot. 30: 165.  For the
relationship between action spectrum and quantum yield you might 
consut P.S. Nobel(1991) Physiochemical and Environmental Plant 
Physiology, Academic Press.  I hope this helps.

>Varying the levels of UV could do things ranging from nothing (depending on
>the species and the amount of UV and its wavelength, to killing the platns
>if you hit them hard enough for long enough.  If you are interested in the
>possibility that UV will help the plants or augment the growth that results
>from visible light, I think you can forget it.

>In article <bmm.765614307 at ardu.dsto.gov.au>, bmm at ardu.dsto.gov.au (B.M.
>Murrell (Bruce)) wrote:

>> Could anyone provide information on the which wavlengths of light provide
>> the best growth rate for plants.  I need information for a project I am
>> devising and would appreciate any help I could get.  I also need to know
>> what the effect of varying levels of UV have on plant growth.
>> Thankyou, Bruce Murrell
>> bmm at ardu.dsto.gov.au
>> --
>> SGT B.M. (Bruce) Murrell
>> Aircraft Research & Development Unit (ARDU)
>> Royal Australian Air Force (RAAF)
>> 61-8-256-3116

>John Cheeseman                                 "We haven't the money,
>Department of Plant Biology                     so we've got to think."
>University of Illinois                          -- Lord Rutherford (1962)
>Urbana IL 61801 USA
John Markwell			Phone: 402-472-2924
Dept. Biochemistry		FAX:   402-472-7842
University of Nebraska		Internet: markwell at unl.edu
Lincoln, NE  68583-0718

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