Definition
A unit of luminance (brightness) equal to the brightness of a perfectly diffusing surface that emits or reflects one lumen per square centimeter. Used historically in aviation to specify the brightness of instrument lighting, cockpit displays, and runway/approach lighting.
Plain English
A measurement of how bright a lit surface appears. One lambert is the brightness of a flat surface giving off light evenly in all directions at a set rate.
Context Anchor
Seen in technical discussions of aircraft lighting, instrument displays, airport lighting, and visibility-related light measurements.
Derivation
Named after Johann Heinrich Lambert (1728–1777), the Swiss-German mathematician and physicist who studied how light is reflected and scattered from surfaces. His work on light measurement became the foundation for how brightness is quantified.
Why Pilots Care
Cockpit and instrument lighting must be bright enough to read at night but not so bright that it destroys night vision. Brightness specifications, including those given in lamberts, ensure displays are usable across all flight conditions.
Intuition Check
Do not read Lambert as a person, place, or aircraft part in this context. Here it is a unit for how bright a surface appears.
Example Sentence 1
The instrument panel lighting was specified at a maximum brightness of 1 lambert to preserve the pilot's night vision.
Example Sentence 2
During the preflight, the pilot checked that the chart light output stayed within acceptable lambert values for comfortable reading.