Radiance and spectral radiance are radiometric measures that describe the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction. They are used to characterize both emission from diffuse sources and reflection from diffuse surfaces. The SI unit of radiance is watts per steradian per square metre (W·sr^-1·m^-2). Radiance characterizes total emission or reflection, while spectral radiance characterizes the light at a single wavelength or frequency. The radiance is equal to the sum (or integral) of all the spectral radiances from a surface. Spectral radiance has SI units W·sr^-1·m^-3 when measured per unit wavelength, and W·sr^-1·m^-2·Hz^-1 when measured per unit frequency interval. Radiance is useful because it indicates how much of the power emitted by an emitting or refl

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # TAGS