Luminance Unit Converter

Luminance measures the luminous intensity per unit area emitted or reflected from a surface in a given direction. It describes how bright a surface appears to the human eye and is fundamental in display technology, lighting design, and vision science.

Understanding Luminance

Luminance is the photometric measure of the luminous intensity per unit area of light traveling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given solid angle.

Key Characteristics:

• Physical quantity: Luminous intensity per unit area (cd/m²)
• Human perception: Directly related to brightness perception
• Direction dependent: Varies with viewing angle
• Surface property: Describes how bright a surface appears

Common Luminance Units

Metric Units

• cd/m² (Candela per Square Meter): The SI base unit of luminance
• nits: Alternative name for cd/m², commonly used in display industry
• cd/cm²: Used for very bright sources (10,000 cd/m²)
• mcd/m²: Millicandela per square meter for dim sources

Imperial Units

• Foot-Lambert (fL): Traditional unit equal to 1/π candela per square foot
• Stilb: Equal to 1 candela per square centimeter

Applications

Display Technology

• Computer monitors: Typically 100-400 nits
• TVs: 100-1000 nits for SDR, up to 4000+ nits for HDR
• Mobile devices: 400-1200 nits for outdoor visibility
• Cinema projectors: 48 nits for standard projection

Lighting Design

• Sky luminance: 1,000-10,000 cd/m² on clear days
• Paper in daylight: ~100 cd/m²
• Candle flame: ~1,000 cd/m²
• Sun's surface: ~1.6 billion cd/m²

Vision Science

• Photopic vision: >3 cd/m² (daylight vision)
• Mesopic vision: 0.001-3 cd/m² (twilight vision)
• Scotopic vision: <0.001 cd/m² (night vision)

Luminance vs Illuminance

It's important not to confuse luminance with illuminance:

• Luminance (cd/m²): Light emitted/reflected from a surface (brightness)
• Illuminance (lux): Light falling onto a surface (lighting level)

A white paper has high luminance in bright light but the same illuminance as a black paper beside it.

Measurement and Standards

Luminance is measured using:

• Luminance meters: Direct measurement devices
• Spot photometers: For specific areas
• Imaging luminance meters: For spatial distribution

Standards organizations like CIE (International Commission on Illumination) define measurement procedures and calibration standards for accurate luminance measurements across different industries.