P

In a light beam of a certain power, a corresponding amount of energy will be carried (as photons) by the beam in any given time, and this is related to the photon density. If the beam is high power, or the spot-size is small, then the photon density can be significantly larger than a low power beam with a larger spot size. Photon density is a similar measure to intensity, but considers the photons occupying a volume at any given time.

Related Terms: Photon, Photon Density, Power, Power Density