Luminance Converter

Luminance: The Brightness of Surfaces and Displays

Luminance is the photometric measure of the luminous intensity per unit area of light travelling in a given direction. In simpler terms, it describes how bright a surface appears to a human observer — whether that surface is a smartphone screen, a cinema projection, the overcast sky, or the reflective face of the moon. The SI unit of luminance is the candela per square meter (cd/m²), universally known in the display and cinema industries as the nit.

As display technology has advanced from CRT monitors to OLED, QLED, and MicroLED panels, luminance has become one of the defining specifications that separates entry-level consumer products from professional-grade displays. High Dynamic Range (HDR) content standards, which have transformed both home cinema and professional post-production workflows, are built entirely around peak luminance specifications. Converting between luminance units accurately is critical for display engineers, cinematographers, photometrists, and architectural lighting designers.

The Nit: A Unit Born from Display Technology

While candela per square meter (cd/m²) is the formal SI unit, the term nit (from the Latin nitere, to shine) has become the dominant informal unit in the display industry. Display manufacturers in the United States and globally specify peak brightness, sustained brightness, and HDR tier ratings in nits. One nit equals exactly one cd/m².

HDR standards define luminance tiers that matter enormously to consumers and content creators. The HDR10 standard requires a minimum of 400 nits peak brightness; Dolby Vision supports up to 10,000 nits; and HDR10+ targets up to 4,000 nits. The IMAX Enhanced certification for home displays requires a minimum 600 nits. In a movie theater, the Society of Motion Picture and Television Engineers (SMPTE) standard for 2D projection has historically been approximately 48 cd/m² (about 14 foot-lamberts), while HDR cinema targets 108 cd/m² or higher.

Foot-Lamberts: The Cinema Standard

The foot-lambert (fL) remains the standard unit for cinema projection brightness in the United States, specified in SMPTE and ANSI standards. One foot-lambert equals 1/π candela per square foot, which translates to approximately 3.4262 cd/m². For decades, the standard screen brightness for commercial cinema was 16 foot-lamberts (approximately 55 cd/m²), lowered to 14 fL in the digital projection era.

The foot-lambert survives in the US cinema industry because projector specifications, screen gain tables, throw distance calculations, and photometric reports have been written in these units for over a century. Converting between foot-lamberts and nits is a daily requirement for anyone specifying projection systems for commercial cinemas, theme parks, and corporate presentation environments, which is why this converter explicitly supports it.

Luminance in Architectural Lighting Design

Architectural and workplace lighting standards specify not just illuminance (lux or foot-candles) but also luminance limits to prevent glare. The Unified Glare Rating (UGR) system used in the UK and Europe, and the Visual Comfort Probability (VCP) system used in North America, both depend on the luminance of luminaire surfaces as seen from a given viewing angle. The CIBSE (Chartered Institution of Building Services Engineers) in the UK and IES (Illuminating Engineering Society) in the United States publish recommended luminance limits for office environments, typically capping luminaire luminance at 3,000–10,000 cd/m² depending on the viewing angle and task sensitivity.

In roadway and outdoor lighting, luminance is the preferred metric for evaluating whether a road surface provides adequate visibility for drivers — rather than illuminance, which measures what arrives at the surface, luminance measures what the driver's eye actually receives. British Standard BS 5489 and American ANSI/IES RP-8 both use maintained road surface luminance as a design target.

Extreme Luminance: Natural and Industrial Sources

The human visual system accommodates luminance across an extraordinary range — from about 10⁻⁶ cd/m² (absolute visual threshold in darkness) to over 10⁹ cd/m² (direct view of the sun). The sun's photosphere has a luminance of approximately 1.6 × 10⁹ cd/m², making it incomparably brighter than any manufactured display. A clear blue sky away from the sun measures roughly 5,000–10,000 cd/m². A standard white piece of paper in office lighting registers about 80–120 cd/m².

Industrial high-brightness projectors for outdoor events can reach 50,000–100,000 lumens output, producing screen luminance exceeding 1,000 cd/m² on large format screens. Surgical lighting environments target task-area luminance of 10,000–40,000 lux, which — combined with surface reflectance — produces luminance values many times higher than standard office environments, designed to ensure surgeons can distinguish tissue types with precision.