Allard's law

From Glossary of Meteorology



Allard's law

An equation used in predicting the night visual range of self-luminous targets.

Assume a light source at distance x from an observer and having (monochromatic) luminous power Pv in that person's direction. Then for uniform extinction coefficient σ, the illuminance Ev reaching the observer is
ams2001glos-Ae15
When Ev equals the threshold illuminance for a given background luminance and detection probability, x is the night visual range, or maximum distance for detecting the light source.