What spectrum of light promotes stem growth in plants.?

Question

What spectrum of light promotes stem growth in plants.?

Answer 1

depends on what plant

but most use chlorophyl, which absorbs light at 665nm and 465nm

there are different chlorophyls and some plants or algae use different pigments to absorb other wavelengths

Answer 2

"Red depleted light" (link below).

Red light drives photosynthesis.  So when red light is limited, this suggests that the plant may be under canopy.  This can initiate the shade avoidance response (stimulated growth in attempt to grow above the canopy and reach sunlight).