**Emissive power** of a body at a given temperature is the amount of energy emitted per unit time per unit area of the surface for a given wavelength.

The emissive power of a body is defined as the ratio of the amount of energy emitted (or radiated) per unit area per second to the amount of emitted heat energy per unit area of a perfectly black body per second at the same temperature.

The value of emissive power lies between 0 to 1. The emissive power of a perfectly black body is 1. But, a perfectly white surface or body has the zero emissive power.

**Emissive power is denoted by e _{λ}. **

**Its unit is W m ^{-2}.**