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About Luminance Conversion

Luminance measures the amount of light emitted or reflected from a surface in a particular direction—essentially how "bright" a surface appears to an observer. Unlike illuminance (light falling on a surface), luminance is what your eyes actually perceive. It accounts for both the intensity of light leaving the surface and the area over which it's emitted, making it direction-dependent: the same surface can have different luminance when viewed from different angles. This directional nature is why display specifications must account for viewing angle effects.

The SI unit is candela per square meter (cd/m²), also called the nit in display industry terminology. Luminance spans an enormous range in everyday experience: from 10⁻⁶ cd/m² for the dimmest visible starlight to 1.6 × 10⁹ cd/m² for the sun's surface. Human eyes adapt remarkably well across this range, but comfortable viewing typically falls between 50-500 cd/m². Luminance is crucial for display technology (screen brightness specifications), lighting design, roadway visibility analysis, and visual comfort assessment in work environments.

Our converter handles all standard luminance units used in photometry, display engineering, and architectural lighting.

Common Luminance Conversions

Luminance Unit Reference

Candela per square meter (cd/m²) – The SI unit of luminance, representing light intensity per unit projected area in a specific direction. This is the fundamental unit for all modern display specifications, lighting calculations, and photometric measurements. Typical values: office lighting creates 100-500 cd/m² on white surfaces; computer monitors operate at 200-400 cd/m²; the clear sky is about 8,000 cd/m².

Nit – An informal but widely used name for cd/m², especially popular in the consumer electronics and display industries. "1000 nit display" means 1000 cd/m² peak brightness capability. The term comes from the Latin "nitere" (to shine). HDR display marketing extensively uses nits because it sounds more consumer-friendly than the technical SI unit. 1 nit = 1 cd/m² exactly.

Foot-lambert (fL) – The traditional US unit for luminance, still used in cinema projection standards and some American lighting specifications. 1 fL ≈ 3.426 cd/m². SMPTE cinema standards specify 14-16 fL (48-55 cd/m²) for 2D projection and 3.5-6 fL for 3D. Increasingly replaced by cd/m² in modern specifications.

Stilb (sb) – The CGS unit of luminance. 1 sb = 10,000 cd/m² = 1 cd/cm². Rarely used today except in older scientific literature, as values for most practical surfaces would be inconveniently small fractions.

Lambert (L) – A unit assuming perfectly diffuse (Lambertian) emission or reflection from a surface. 1 L = (1/π) cd/cm² = 3,183 cd/m². The millilambert (mL) is more commonly encountered. Used when analyzing matte surfaces like painted walls or paper where light scatters uniformly in all directions.

Apostilb (asb) – The metric analog of the foot-lambert for diffuse surfaces. 1 asb = (1/π) cd/m² ≈ 0.318 cd/m². Also called the blondel in some European references. Used in some European lighting standards.