Photosynthetic action spectra of several cyanobacteria show a peak at about 650 
nm, the height of which is correlated with allophycocyanin content in the 
strains examined. Allophycocyanin harvests light more efficiently than do 
phycocyanin and phycoerythrin. The contribution of chlorophyll a absorption to 
photosynthetic activity is barely detectable in cells of normal pigment 
composition. Chlorophyll a becomes the major light-harvesting pigment in cells 
that have been physiologically depleted of phycobiliproteins.