 Radiant energy density

Radiant energy density refers to the amount of energy per unit volume carried by electromagnetic radiation, such as light. It is an important concept in fields like astrophysics, optics, and thermodynamics, particularly when studying the behavior of radiation in environments like blackbody radiation, the interstellar medium, or the early universe. Mathematically, radiant energy density \( u \) is typically expressed in units of energy per unit volume, such as joules per cubic meter (J/m³).