Silene armeria was cultured on a medium containing 5% sucrose, and subjected to various light conditions. 1. Plants subjected to continuous illumination of far-red radiant energy exclusive of other spectral regions initiated flower buds most readily. Far-red light mixed with other spectral regions was less effective in promoting flowering than far-red light alone. 2. The plants subjected to short photoperiods initiated no flower buds irrespective of the quality of light in the light period. 3. Red light was more effective in promoting flowering than daylight fluorescent light but was less effective than the far-red light.