辐射度量学是研究各种电磁辐射强弱的学科。

辐射度量学中最基本的物理量就是辐射通量，是单位时间内通过某一面积的所有电磁辐射（包括红外、紫外和可见光）总功率的度量，既可以指一辐射源发出辐射的功率，也可以指到达某一特定表面的辐射能量的功率。单位是瓦特。

对于非单色辐射，人们往往关心能量的频谱分布，叫做辐射通量的谱密度。单位是瓦特/赫兹。

瓦特每平方米每赫兹

L_eν

瓦特每球面度每平方米每赫兹

Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye. Radiometry is distinct from quantum techniques such as photon counting.