Considerations when setting up your germination red light experiments
Why use a red filter? Answer - The original scientific paper , J. Amer. Soc. Hort Sci.,volume 120, pages 953-955, (1995) by Y. Yambe, K. Takeno, and T. Saito tested white light provided by cool white fluorescent tubes, red light provided by a red cellophane sheet and blue light provided by a blue cellophane sheet. The red filtered light provided the highest percentage (around 38 to 58%), white light provided a germination percentage of around 15 to 28 %. It appears that blue light is absorbed by both forms of the phytochrome and is to be avoided. This is the reason for the red filter.
The following are from the book "Seeds" by Carol C. Baskin
and Jerry M. Baskin, Academic Press, 1998, pages 14 and 15.
"Cool white fluorescent tubes are a better light source for germination studies than
incandescent light bulbs. Cool white fluorescent tubes emit considerable red but very
little far-red (Toole, 1963)...."
".... This means that one or two 20-W cool white fluorescent tubes 15-20 cm above
each incubator shelf will provide enough light for germination, if the lights are on for
several hours each day."
"...light of "...almost any quality inhibits germination if applied at high
irradiances for sustained periods: (Roberts Et al., 1987). The maximum photon dose
(=incident photon flux area density X duration of exposure) of light that can be given to
seeds without inhibition of germination varies with the species (Ellis et al., 1986a) and
among seeds of the same species (Ellis et al., 1986b)."
"Photoperiod, potassium nitrate, and temperature may also influence the maximum
photon dose for promotion or inhibition of germination."
"Because the high irradiance reaction overrides the reversible phytochrome reactions
(Borthwick et al., 1969; Bartley and Frankland, 1982), exposure to continuous light during
germination tests may inhibit germination.."
Thus it appears that one should not leave the lights on continuously. I now use timers that keep the lights on during the day but shut them off at night.
I did try both 24 hours and the 12 hours and did seem to get slightly better
germination with the 12 hour on experiment. However, turning the lights off also
probably produced a cooling effect which also may have been the cause of the slight
increase in germination as compared to the 24 hour on experiment.