When you flip a light switch, a current of electricity passes through your light bulb. The filament in the light bulb then heats up, eventually producing a glow or the "light" we are used to seeing. Believe it or not, most light bulbs are more adept at producing heat than they are at producing light. Traditional incandescent bulbs waste far more energy than other sources of light simply because a light bulb produces so much heat. That is of course unless you use your light bulbs to heat a room!