Inoptics thenoise-equivalent flux density (NEFD) ornoise-equivalent irradiance (NEI) of a system is the level offlux density required to be equivalent to thenoise 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'snoise-equivalent power for a collection areaA and a photon bandwidth${\displaystyle \nu }$ by:

${\displaystyle \mathrm{N}\mathrm{E}\mathrm{F}\mathrm{D}=\eta \frac{\mathrm{N}\mathrm{E}\mathrm{P}}{A\nu }}$,

where a factor${\displaystyle \eta }$ (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.

External quantum efficiency

Thisoptics-related article is astub. You can help Wikipedia byexpanding it.

• v
• t
• e

• Physical quantities
• Engineering ratios
• Photodetectors
• Quantum electronics
• Spectroscopy
• Optics stubs

• Articles with short description
• Short description matches Wikidata
• All stub articles