Far-red light

[5] In plants, the photoreceptors cryptochrome and phototropin absorb radiation in the blue spectrum (B: λ=400–500 nm) and regulate internal signaling such as hypocotyl inhibition, flowering time, and phototropism.

The inactive conformation will remain in the cytosol, allowing PIFs to target their binding site on the genome and induce expression (i.e. shade avoidance through cellular elongation).

In the early 1970’s, PhD physicist and soil crop professor Dr. Keith J. McCree lobbied for a standard definition of photosynthetically active radiation (PAR: λ=400–700 nm) which did not include FR.

[11] More recently, scientists have provided evidence that a broader spectrum called photo-biologically active radiation (PBAR: λ=280–800 nm) is more applicable terminology.

The Emerson Effect established that the rate of photosynthesis in red and green algae was higher when exposed to R and FR than the sum of the two individually.