In astronomy, a photometric system is a set of well-defined passbands (or optical filters), with a known sensitivity to incident radiation.
For each photometric system a set of primary standard stars is provided.
[citation needed] Photometric systems are usually characterized according to the widths of their passbands: Each letter designates a section of light of the electromagnetic spectrum; these cover well the consecutive major groups, near-ultraviolet (NUV), visible light (centered on the V band), near-infrared (NIR) and part of mid-infrared (MIR).
[a] The letters are not standards, but are recognized by common agreement among astronomers and astrophysicists.
Units of measurements: Note: colors are only approximate and based on wavelength to sRGB representation (when possible).