Noise-equivalent flux density explained

In optics the noise-equivalent flux density (NEFD) or noise-equivalent irradiance (NEI) of a system is the level of flux density required to be equivalent to the noise present in the system.^[1] It is a measure used by astronomers in determining the accuracy of observations.^[2]

The NEFD can be related to a light detector's noise-equivalent power for a collection area A and a photon bandwidth

\nu by:NEFD = η (NEP)/(A \nu) ,

where a factor

η (often 2, in the case of switching between measuring a source and measuring off-source) accounts for the photon statistics for the mode of operation.

See also

External quantum efficiency

Notes and References

1. Book: Malacara, Daniel . Physical Optics and Light Measurements . 247 . 1988 . . 9780124759718 .
2. Benford . D. J. . Hunter . T. R. . Phillips . T. G. . Noise Equivalent Power of Background Limited Thermal Detectors at Submillimeter Wavelengths. International Journal of Infrared and Millimeter Waves . 19 . 7 . 931 . 1998 . 10.1023/A:1022671223858 . 1998IJIMW..19..931B . 9196659 .