Luminance Converter
Convert between candela per square meter, foot-lambert, stilb, and other luminance units
About Luminance Measurement
What is Luminance?
Luminance is a photometric measure that quantifies the amount of light emitted, transmitted, or reflected from a surface per unit area in a given direction. It represents the brightness of a surface as perceived by the human eye and is fundamental to understanding how light interacts with materials and surfaces.
The mathematical definition of luminance is:
L = dI / (dA × cos θ)
Where: L = Luminance, dI = Luminous intensity, dA = Area, θ = Angle between surface normal and viewing direction
Common Luminance Units and Conversions
| Unit | Symbol | Definition | Conversion to cd/m² |
|---|---|---|---|
| Candela per square meter | cd/m² | SI base unit | 1 |
| Nit | nt | Display industry standard | 1 |
| Foot-lambert | fL | US cinema standard | 3.426 |
| Lambert | L | CGS unit | 3,183 |
| Stilb | sb | CGS unit | 10,000 |
| Apostilb | asb | Non-SI unit | 0.3183 |
Luminance Types and Real-World Applications
| Luminance Type | Typical Range | Applications | Examples |
|---|---|---|---|
| Display Luminance | 100-1,000 cd/m² | Screens, monitors, TVs | iPhone display: 800 cd/m², HDR TV: 1,000+ cd/m² |
| Ambient Lighting | 10-500 cd/m² | Indoor environments | Office lighting: 300 cd/m², home: 100 cd/m² |
| Automotive Lighting | 1,000-20,000 cd/m² | Headlights, taillights | LED headlight: 15,000 cd/m², brake light: 5,000 cd/m² |
| Natural Light Sources | 1,000-2×10⁹ cd/m² | Sun, moon, sky | Sun surface: 2×10⁹ cd/m², full moon: 2,500 cd/m² |
| Medical Imaging | 50-500 cd/m² | Diagnostic displays | X-ray monitor: 400 cd/m², ultrasound: 250 cd/m² |
Luminance Measurement Tools and Instruments
Photometers
- • Spot photometers: Measure luminance at specific points
- • Imaging photometers: Create luminance maps of entire scenes
- • Color photometers: Measure both luminance and chromaticity
- • Portable photometers: Field measurements and calibration
Calibration Standards
- • Standard light sources: NIST-traceable calibration
- • Luminance standards: Certified reference materials
- • Integrating spheres: Uniform luminance sources
- • Blackbody radiators: Temperature-based standards
Luminance vs Brightness vs Illuminance: Key Differences
Fundamental Distinctions
The relationship between these quantities is governed by the photometric law:
E = L × π × cos θ
Where: E = Illuminance, L = Luminance, θ = Angle of incidence
Luminance-Perception Relationship and Human Vision
Human visual perception follows a logarithmic relationship with luminance, described by the Weber-Fechner law:
ΔS = k × (ΔL / L)
Where: ΔS = Perceived brightness change, ΔL = Luminance change, L = Base luminance, k = Constant
Visual Comfort Ranges
- • Reading: 100-500 cd/m²
- • Computer work: 200-400 cd/m²
- • General lighting: 50-300 cd/m²
- • Night vision: 0.01-1 cd/m²
Adaptation Effects
- • Scotopic vision: Rod-dominated, low luminance
- • Mesopic vision: Mixed rod-cone response
- • Photopic vision: Cone-dominated, high luminance
- • Adaptation time: 5-30 minutes for full adaptation
Why Luminance Measurement Matters: Industries and Safety
Safety and Compliance
- • Workplace safety: OSHA lighting standards
- • Road safety: Automotive lighting regulations
- • Aviation: Runway and aircraft lighting requirements
- • Medical: Diagnostic display calibration standards
Quality Control
- • Display manufacturing: Consistency and performance
- • Lighting design: Architectural and theatrical applications
- • Photography: Exposure and color accuracy
- • Printing: Color matching and proofing
Frequently Asked Questions About Luminance
How does luminance affect energy efficiency?
Higher luminance typically requires more power, but modern LED technology provides excellent efficiency. The relationship follows: Power = Luminance × Area × Efficacy, where efficacy is measured in lumens per watt (lm/W).
What's the difference between luminance and radiance?
Luminance measures visible light as perceived by human vision (photometric), while radiance measures total electromagnetic radiation (radiometric). Luminance is weighted by the human eye's spectral sensitivity curve.
How do I measure luminance accurately?
Use a calibrated photometer with proper cosine correction, ensure the measurement angle is perpendicular to the surface, avoid ambient light interference, and calibrate regularly against known standards.
Why is luminance important in display technology?
Luminance determines display visibility in different lighting conditions, affects power consumption, influences color accuracy, and impacts user comfort and eye strain during extended viewing periods.
Frequently Asked Questions About Luminance Conversion
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