不同光源，由于发光的物质不同，辐射能（辐射功率）按照波长分布的情况也就不一样。

A spectral energy distribution (SED) is a plot of brightness or flux density versus frequency or wavelength of light. It is used in many branches of astronomy to characterize astronomical sources. For example, in radio astronomy, an SED with a negative spectral index around −0.7 would indicate a synchrotron radiation source. In infrared astronomy, SEDs can be used to classify young stellar objects.