903. Which gives off more heat energy, an incandescent light bulb or a fluorescent lamp? Which is more efficient to use in the summer or winter? — TJ, Woodbridge, VA
An incandescent lamp turns its electric power completely into heat. Even the visible light it gives off is actually thermal radiation. A fluorescent lamp tries not to produce heat—the light it produces is non-thermal (it doesn't involve hot materials). While a fluorescent lamp is only partly successful at not producing heat, it's still several times more energy efficient than an incandescent lamps—fluorescents produces several times as much illumination for the same amount of electric power. This statement is true both in summer and winter, although fluorescent bulbs lose some of their energy efficiencies in very cold or very hot weather. Fluorescent lamps work best at temperatures between about 15° C and 40° C.