Experimental designs for photoacceleration of embryonic development of chickens used by previous workers were re-examined and compared by 1) light intensity, 2) total energy and 3) photon energy. When compared in this manner, it was obvious how "light" could both increase and decrease hatching time, increase and decrease embryo weights and other variables.Wavelengths of light between 230 and 385 nm. were introduced during incubation. Light at 295 nm. appears to activate embryonic weight gains.