Phytochrome and daylength.

[DavidCampen]

The plant pigment phytochrome exists in 2 forms called Red (Pr) and Far-Red (Pfr). When Pr absorbs light red light of around 670 nm it is converted into Pfr. During the night Pfr slowly changes back into Pr. It has been shown that the photoperiodism of some plants is determined (at least in part) by how low the Pfr concentration drops during the night. In the winter the long nights allow more time for Pfr to convert back to Pr and some plants that require long nights to initiate flowering use Pfr concentrations to determine when floweing begins.

Another way to convert Pfr back to Pr is to expose it to light at 730 nm which quickly converts Pfr to Pr.

Phytochrome

What I would like to see are some experiments with long night flowering orchids where 730 nm far red lght is used to artificially create long nights.

Since my orchid solarium connects to my living room via large glass doors and I also like to work out there late at night I am worried that some of my orchids that require long nights to flower may not flower. I am considering adding some 740 nm LED lights to use during winter nights to simulate long nights.