What this tool does
This luminance converter allows you to convert between various units of luminance, which measures the intensity of light emitted or reflected from a surface per unit area in a given direction. Luminance is what determines how "bright" a surface appears to human eyes. The tool supports conversion between SI units (candela per square meter), CGS units (stilb, apostilb, lambert), and imperial units (foot-lambert). Whether you're calibrating displays, working in photography, or designing lighting systems, this tool provides accurate conversions between all major luminance units.
Supported units
1. Candela per square meter (cd/m²) - The SI unit of luminance, measuring luminous intensity per unit area. 2. Nit - Identical to cd/m², commonly used in the display industry to specify screen brightness. 3. Stilb (sb) - A CGS unit equal to 10,000 cd/m², used in older scientific literature. 4. Apostilb (asb) - A CGS unit equal to 1/π cd/m², historically used for measuring diffuse reflectors. 5. Lambert (L) - A CGS unit equal to 10,000/π cd/m², common in older photometry references. 6. Foot-lambert (fL) - An imperial unit approximately equal to 3.426 cd/m², still used in US cinema projection standards.
Conversion formulas
All conversions use candela per square meter (cd/m²) as the intermediate base unit:
- 1 nit = 1 cd/m² - 1 stilb (sb) = 10,000 cd/m² - 1 apostilb (asb) = 1/π cd/m² ≈ 0.3183 cd/m² - 1 lambert (L) = 10,000/π cd/m² ≈ 3,183.1 cd/m² - 1 foot-lambert (fL) ≈ 3.426 cd/m²
To convert from unit A to unit B: First multiply by the factor to convert A to cd/m², then divide by the factor to convert cd/m² to B.
Common applications
1. Display calibration - Monitor and TV manufacturers specify brightness in nits (cd/m²). Professional displays for HDR content may reach 1000-4000 nits. 2. Photography and cinematography - Light meters and exposure calculations often involve luminance measurements to ensure proper exposure. 3. Lighting design - Architects and lighting designers use luminance calculations to ensure adequate illumination while preventing glare. 4. Cinema projection - The SMPTE standard specifies screen luminance in foot-lamberts (typically 14-22 fL for 2D and 3.5-7 fL for 3D). 5. Automotive displays - Dashboard and infotainment displays must be readable in bright sunlight (requiring 500+ nits) while not blinding at night.
How to use
1. Enter the luminance value you want to convert in the input field. 2. Select the unit of your input value from the "From Unit" dropdown. 3. Select your desired output unit from the "To Unit" dropdown. 4. The conversion result appears automatically in the hero result card. 5. Use the "Swap Units" button to quickly reverse the conversion direction. 6. Click "Copy Result" to copy the converted value to your clipboard.
Worked examples
Example 1: A smartphone display has a peak brightness of 800 nits. What is this in foot-lamberts? 800 nits × (1 fL / 3.426 cd/m²) = 233.5 fL
Example 2: A cinema screen is calibrated to 16 foot-lamberts. What is this in cd/m²? 16 fL × 3.426 cd/m²/fL = 54.8 cd/m²
Example 3: An old photometry reference specifies a surface luminance of 0.5 lamberts. Convert to nits: 0.5 L × (10,000/π) cd/m²/L ≈ 1,591.5 cd/m² = 1,591.5 nits
FAQs
Q: What is the difference between luminance and brightness? A: Luminance is an objective, measurable physical quantity (cd/m²), while brightness is the subjective perception of light intensity. Two surfaces with the same luminance may appear differently bright depending on surrounding conditions.
Q: Why do displays use nits instead of cd/m²? A: "Nit" is simply a more marketable term than "candela per square meter." They are identical units (1 nit = 1 cd/m²).
Q: What luminance level is comfortable for indoor display viewing? A: For office environments, 200-300 cd/m² is typically comfortable. For HDR content viewing in a dark room, peak brightness of 1000+ nits with an average picture level of 100-200 nits works well.
Q: Why are foot-lamberts still used in cinema? A: The US cinema industry established standards using foot-lamberts decades ago, and these standards (like SMPTE 196M specifying 16 ± 2 fL for 2D projection) remain in use for backwards compatibility.
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