Which statement best describes the relationship between tungsten bulbs and heat output?

Which statement best describes the relationship between tungsten bulbs and heat output?

• A. They produce most of their energy as heat (80%) and little as light (20%)
• B. They produce mostly light with little heat
• C. They are 100% efficient
• D. They produce equal heat and light

Answer: (A)

Tungsten bulbs work by heating a tungsten filament until it glows, and at those high temperatures the emission is dominated by infrared radiation, i.e., heat. Only a portion of that energy comes out as visible light. So the energy distribution is heavily weighted toward heat, with relatively little visible light produced. That’s why the statement that they produce most energy as heat and only a portion as light is the best description. They are far from 100% efficient and do not produce equal amounts of heat and light; the visible-light output is small enough that the bulb feels warm even while lighting a room.

Tungsten bulbs work by heating a tungsten filament until it glows, and at those high temperatures the emission is dominated by infrared radiation, i.e., heat. Only a portion of that energy comes out as visible light. So the energy distribution is heavily weighted toward heat, with relatively little visible light produced. That’s why the statement that they produce most energy as heat and only a portion as light is the best description. They are far from 100% efficient and do not produce equal amounts of heat and light; the visible-light output is small enough that the bulb feels warm even while lighting a room.