How Much Heat Does a Light Bulb Put Out?

A 50-watt incandescent light bulb, the most common type of light bulb found in most households, converts 50 joules of electricity into heat and light every second. Of this, 98 percent is converted to heat and 2 percent to light.

Similarly, a 100-watt light bulb converts 100 joules of electrical energy to heat and light every second, with 98 percent of that converted to heat and the remaining 2 percent to light. The average incandescent light bulb is hot to the touch shortly after it is activated as a result of its tendency to generate a disproportionate amount of heat versus light.