What is the optimal wavelength of light for growing plants
Michael L Roginsky
d_micro at ix.netcom.com
Fri Oct 24 16:03:23 EST 1997
In <01bcdbb7$6179c680$2a9d0ccb at rd> "Ross Drewe" <nospam at nospam.com>
> >Plants, for the most part, are uninterested in red and infra-red
> >radiation. They do their photosynthesis thing with the light from
> >the sun; in order to do this most efficiently, they are most
> >responsive to light at the wavelengths of the peak output from the
> >sun, namely the middle of the visible spectrum, i.e. green -- not
> >coincidently the color of peak visual acuity of the human (among
> >others) eye, which is as efficient as it is because it, like
> >is at its best for the wavelengths most available in sunlight.
>This posting appears to express what the author would like to be true,
>not what actually is true.
>It is *very* well established that photosynthesis in all higher plants
>uses mostly blue and red light - exactly the opposite of what is
>claimed above. Jim Ivey is correct in saying that the absorption peaks
>for chlorophyll are in the blue and red. I would like to add that the
>actual effectiveness of the light of different wavelengths in
>photosynthesis does not necessarily coincide with the absorption
>spectra of the chlorophylls. It is influenced by other light absorbing
>pigments and varies from plant to plant. It is expressed as an
>'activity spectrum' and has to be experimentally determined for each
>species (by measuring photosynthetic rates). However, it remains true
>that it is the red and blue parts of the spectrum which are used.
> >The same evolutionary pressure has made eyes and plants most
> >sensitive to green light, which is why the grass is green.
>This is also nonsense. If there is any truth in the argument, it would
>be the other way around - we would see best in the green because
>have been using chlorophyll for much longer than we have been
>As it happens, we do NOT have maximum visual sensitivity for the
>midgreen, where chlorophyll reflects best (see below). In view of the
>complexity of the photosynthetic pathways and the limited number of
>photosynthetic pigments which appear to work (across the whole animal
>kingdom), it appears that evolution has NOT been free to match the
>maximal visual sensitivity with the colours in the environment.
> >they are most responsive to light at the wavelengths of the PEAK
> >output from the sun, namely the middle of the visible spectrum,
> >i.e. green
>Wrong. The peak energy in sunlight is in the blue, not the green. The
>spectrum of sunlight above the atmosphere is reasonably approximated
>black body radiation at around 5800K, over an extended range (say,
>0.2-2 microns). At the earth's surface, it is modified by atmospheric
>absorption - it lacks a lot of the UV, especially the shorter
>wavelengths, and there are sharply defined chunks out of the
>However, the bulk of the energy is still in the blue at ground level.
>Furthermore, there is no reason why evolution should put the peak
>sensitivity at the peak of the sunlight spectrum. In fact, it should
>logically be the other way round. Increasing the sensitivity of the
>in spectral regions which are relatively deficient in sunlight would
>the obvious way to maximise information across the widest possible
>spectrum. And this does happen in nature: many animals make good use
>a visual range which, for them, extends into the UV. For some animals,
>information from the UV is critical to some of their normal
>It's the information that counts, not how brightly the scene is lit.
>There may even be animals that use infra-red to some extent in vision,
>despite its low photon energies - I don't know any off hand, perhaps
>someone else can give examples.
> >i.e. green -- not coincidently the color of peak visual acuity of
> >the human (among others) eye,
>Wrong again. In sunlit conditions ('photopic' conditions) our
>wavelength of maximum sensitivity is more towards the yellow (around
>555nm) than the midgreen typical of sunlit plants.
To make it simple, look at the info provided by GE and Sylvania on
their electro-luminescent tubes used to start plant seedlings indoors.
Very little in the red and below bandwidht, increasing with shorter
wavelenghts into the blue and above. Cheers.....Micro.
More information about the Plantbio