Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Number of photons emitted by a lightbulb per second

Roughly how many photons are emitted by a 100-W lightbulb in 1 second?

People tend to remember wavelengths rather than frequencies for visible light. The bulb emits photons with a range of frequencies and wavelengths, but let's take 600 nm as a typical wavelength for purposes of estimation. The energy of a single photon is

A power of 100 W means 100 joules per second, so the number of photons is

Last Update: 2009-06-21