Specific intensity (ln) is a measure of the amount of energy radiated by a source in a particular direction per unit solid angle.

Common units related to specific intensity include watts per square meter per steradian (W/m^2/sr) in the SI system, and ergs per second per square centimeter per steradian (erg/s/cm^2/sr) in the CGS system.

• Specific intensity is crucial in fields like astronomy to measure the brightness of celestial objects.
• It is used in radiometry to quantify the intensity of radiation in different directions.