Luminance Converter

Convert luminance between candela per square metre and foot-lamberts, describing how bright a surface actually appears.

Luminance Measures Perceived Brightness of a Surface, Not Total Light Output

Luminance measures how bright a surface actually appears to an observer, combining the light being emitted or reflected from that surface with the specific area it’s coming from, which is exactly why luminance is the relevant measurement for display and screen brightness, since two screens emitting identical total light output can appear very differently bright to a viewer if that light is being emitted from surfaces of different sizes, concentrating or spreading the same total light output across a smaller or larger visible area. This distinguishes luminance clearly from luminous intensity, covered separately, which measures total light output in a given direction regardless of the emitting surface’s size, meaning luminance specifically answers “how bright does this surface look” while luminous intensity answers “how much light is this source producing,” two genuinely different questions that happen to both get colloquially called “brightness” in everyday, imprecise conversation. Candela per square metre, the SI unit, is used directly in display technology specifications, camera and cinema industry standards, and architectural lighting design, wherever the actual perceived brightness of a specific visible surface, rather than a light source’s total output, is the quantity that genuinely matters for the application at hand.