Sunlight emits all colors of the rainbow plus invisible ultraviolet and far-red energy. Electric lamps emit most of these colors, but in different proportions than sunlight. Incandescent lamps, such as the common light bulb, emit a higher ratio of red to blue light compared to cool white fluorescent tubes that emit higher ratios of blue light. Lamps that emit higher ratios of red light enhance the poinsettia bract color. Under blue light, red bracts have a dull bluish-red appearance and look old.
Most retail stores use cool white fluorescent tubes because they are more energy efficient.
Many large buildings, like exhibition halls, use mercury vapor lamps. Unfortunately, these light sources drastically dull bract colors. For best bract color when displaying poinsettias, use incandescent or color corrected lamps with a high ratio of red to blue light. Use these as supplemental spot lights to enhance the appearance of poinsettias that are for sale. At least, provide good quality light for red cultivars.