Incoherent sources emit light with frequent and random changes of phase between the photons. (Tungsten filament lamps and 'ordinary' fluorescent tubes emit incoherent light). Conventional light sources are incoherent sources.

What is incoherent light in physics?

Incoherent light does not contain photons with the same frequency and does not have wavelengths that are in phase with one another. This type of light is diffuse, like that of a flashlight, rather than a steady stream of light as with a laser.

What type of light produces incoherent light?

Regular light, such as from an incandescent light bulb or from a fire, is incoherent. The light from a fire contains different light waves that are not the same frequency, are not in phase, are not traveling in the same direction, and are not in the same polarization state.