The source radiates into a narrow cone with an opening angle of a few hundredths of a milliradian or less for undulators, or a few tenths of a milliradian for bend magnets.
Spectral brightness is the brightness per unit spectral bandwidth.
Experiments with synchrotron light tend to fall into three categories. Brightness brings distinct advantages to each of these kinds of experiments. A typical benefit accrues to the study of solid surfaces, which are mostly heterogeneous, making it hard to interpret spectroscopic data obtained by illuminating the entire surface. With spatial resolution, spectral features could be directly associated with specific surface areas and structures. For the spectroscopist, brightness allows high spectral resolution without the usual penalty of reduction in signal and increase in measuring time.