Luminance Converter

Luminance measures how bright a surface appears to the human eye when viewed from a given direction — the luminous intensity emitted, transmitted, or reflected per unit area. It's the quantity that determines whether a screen looks bright enough in sunlight, whether a road sign is visible at night, or how a photographer's light meter reading translates into an actual exposure setting.

Our Luminance converter supports the SI unit, candela per square meter (cd/m², also called the nit), along with candela/square centimeter, candela/square foot, and candela/square inch for different measurement scales. Kilocandela/square meter handles very bright sources conveniently. The stilb (cd/cm²) is a CGS unit still occasionally used in photometry, and lumen/steradian per unit area units (per square meter, centimeter, or foot) express luminance in terms of luminous flux rather than intensity. A specialized radiometric unit, watt/square centimeter/steradian (at 555 nm, the wavelength of peak human eye sensitivity), links luminance to absolute radiometric power for scientific applications.

For older and CGS-based photometry, the converter includes the lambert and millilambert, foot-lambert (still common in cinema and projector brightness specifications), apostilb, blondel (identical to apostilb), bril, and skot (a unit for very low luminance levels, used in low-light vision research). Having all of these available in one tool means a historical measurement or an older lighting standard can be converted directly into modern nit-based specifications.

To use the converter, select your starting and target units from the dropdown lists and enter a value — the result is calculated instantly to up to 12 significant digits. For example, converting a smartphone display's typical brightness of 500 nits to foot-lamberts gives about 146 fL, a figure directly comparable to cinema screen brightness standards (which target around 14-16 fL for projected film).

Luminance conversions matter across display technology (comparing brightness specifications between manufacturers who may quote nits, cd/m², or foot-lamberts), photography and cinematography (exposure calculations and light meter readings), architectural and roadway lighting design (glare and visibility standards reference luminance, not just illuminance), and vision science (studying how the eye responds across an enormous range of luminance levels, from starlight to direct sunlight). Because luminance spans such a wide range of values and unit conventions across industries, a single reliable converter avoids costly specification errors.

All conversion factors used in this tool are drawn from standard, internationally recognized photometric unit definitions, so results are dependable for display engineering, photography, and lighting design work. The converter is free, requires no account, and works equally well on desktop and mobile devices.

Luminance is also closely related to illuminance, elsewhere in this Light Converters section — a surface's luminance depends on both how much light falls on it (illuminance) and how well it reflects that light (its reflectance), so the two converters are often used together when working through a complete lighting design calculation.