Luminance Converter

Convert between candela per square meter (cd/m²), nit, foot-lambert, stilb, apostilb, lambert, and more

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Common Presets
What is Luminance?

Luminance is a 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.

In simpler terms, luminance measures how much light is coming from a surface that appears to the human eye. It's what we perceive as brightness.

Importance of Luminance Conversion

Luminance conversion is essential in many fields:

  • Display technology: Comparing brightness specifications of monitors, TVs, and mobile devices
  • Lighting design: Ensuring proper illumination levels in architectural spaces. For broader illumination context, you might also explore light intensity measurements.
  • Photography and cinematography: Matching exposure levels across different equipment
  • Vision science: Researching human visual perception thresholds
  • Automotive industry: Standardizing dashboard and headlight brightness
Unit Symbol Definition
Candela per square meter cd/m² SI unit of luminance (1 cd/m² = 1 nit)
Nit nt Synonym for cd/m², commonly used in display specifications
Foot-lambert fL 1 fL = 3.426 cd/m² (used in cinema brightness measurements)
Stilb sb CGS unit (1 sb = 10,000 cd/m²)
Lambert L 1 L = 3183 cd/m²
Apostilb asb 1 asb = 0.3183 cd/m²
Millinit mnt 1 mnt = 0.001 cd/m² (used for very dim displays)
Candela per square foot cd/ft² 1 cd/ft² ≈ 10.764 cd/m²
Conversion Formulas

All conversions are based on these fundamental relationships:

  • 1 cd/m² = 1 nit
  • 1 cd/m² = 0.2919 foot-lambert
  • 1 cd/m² = 0.0001 stilb
  • 1 cd/m² = 0.000314 lambert
  • 1 cd/m² = 3.1416 apostilb
  • 1 cd/m² = 1000 millinit
  • 1 cd/m² ≈ 0.0929 cd/ft²

To convert between any two units, first convert the source unit to cd/m², then convert from cd/m² to the target unit.

Example Conversions
  • 500 cd/m² = 145.94 foot-lamberts
  • 1 stilb = 10,000 cd/m²
  • 100 foot-lamberts = 342.6 cd/m²
  • 1 lambert = 3183 cd/m²
  • 1000 apostilbs = 318.3 cd/m²

Luminance measures the brightness of a surface as perceived by the human eye (light coming from a surface). Illuminance measures the amount of light falling on a surface (light incident on a surface). Luminance is measured in cd/m², while illuminance is measured in lux (lx). You can explore this further with our light intensity conversion tool.

Different industries and historical periods developed their own units for measuring brightness. The SI unit (cd/m²) is now standard, but legacy units persist in specific fields like cinema (foot-lamberts) or lighting design (candelas per square foot).

Most smartphone screens range from 400-1000 cd/m² in normal use, with some reaching 1500 cd/m² or more for HDR content in bright sunlight.

Monitor brightness controls typically adjust the backlight intensity, which directly affects luminance. A brightness setting of 100% usually corresponds to the display's maximum luminance specification (often 250-400 cd/m² for office monitors).

The SMPTE recommends 14-16 foot-lamberts (48-55 cd/m²) for home theater projectors in a completely dark room. This equates to about 14-16 fL on the screen.

Learn Luminance Concepts

Understanding brightness measurements made simple for students and beginners.

What This Converter Teaches

  • How different industries measure brightness
  • The relationship between scientific units (SI) and practical units
  • Why we need multiple brightness measurement systems
  • How to convert between display specifications
  • Real-world brightness comparisons

Quick Visual Guide

Think of luminance as:
• How bright a light source APPEARS to your eyes
• The "glow" coming from a screen or surface
• Different from total light output (that's luminous intensity)
• Different from light falling on something (that's illuminance)

Unit Meanings in Simple Terms

cd/m² & Nit

Think: Standard brightness unit.
Like: How bright 1 candle spread over 1m² would look.
Use for: All modern displays, scientific work.

Foot-Lambert (fL)

Think: Cinema brightness unit.
Like: Old film projector brightness measurement.
Use for: Movie theaters, projectors.

Stilb (sb)

Think: Very bright sources unit.
Like: 10,000× brighter than cd/m².
Use for: Arc lamps, some industrial lighting.

When to Use Each Unit

UnitBest Used ForCommon In
cd/m² / NitAll modern applicationsSmartphones, TVs, monitors
Foot-lambertCinema and projectionMovie theaters, home theater setups
LambertHistorical referencesOld physics textbooks
MillinitVery dim displaysNight vision devices, astronomy
cd/ft²US lighting industryArchitectural lighting plans

Real-World Examples

Smartphone Screen
500 cd/m² = 146 fL
That's about 10× brighter than a cinema screen!
Office Monitor
300 cd/m² = 88 fL
Comfortable for daily 8-hour work
Cinema Screen
14 fL = 48 cd/m²
Dark room makes this appear brighter

Step-by-Step Conversion Thinking

  1. Identify your starting unit - What does your number represent?
  2. Convert to cd/m² first - This is our common reference point
  3. Remember the multipliers - Each unit has a fixed relationship to cd/m²
  4. Convert to target unit - Multiply or divide using the conversion factor
  5. Check if it makes sense - Does the result seem reasonable?
Example in your head: "100 foot-lamberts to cd/m²... I know 1 fL = 3.426 cd/m²... So 100 × 3.426 = 342.6 cd/m²... That's a typical monitor brightness. Makes sense!"

Understanding Your Results

  • Small number → Big number: You're converting to a smaller unit (like cd/m² to millinit)
  • Big number → Small number: You're converting to a larger unit (like millinit to cd/m²)
  • Same ballpark numbers: Units are similar in scale (like cd/m² and fL)
  • Very different numbers: Units are vastly different (like stilb and apostilb)

Common Student Mistakes

Avoid these!
  • Mixing up luminance (cd/m²) with illuminance (lux)
  • Forgetting that nit = cd/m² (they're identical!)
  • Thinking foot-lamberts are for floor lighting (they're not!)
  • Using wrong decimal places in stilb conversions (it's 10,000×, not 1,000×)
  • Confusing lambert with lumen (different concepts!)

Exam & Study Tips

Memorization Shortcuts
  • cd/m² → fL: Multiply by 0.292 (≈ 0.3)
  • fL → cd/m²: Multiply by 3.426 (≈ 3.4)
  • Stilb rule: "Still Bright" = 10,000× cd/m²
  • Lambert: Roughly 3,000× cd/m²
  • cd/ft²: About 11× cd/m²
Visual Memory Aids
  • Picture a candle on a 1m² card = cd/m²
  • Cinema projector shining = foot-lamberts.
  • Car headlight = stilb (very bright!)
  • Full moon = about 0.25 cd/m²
  • Smartphone in sunlight = 1000+ cd/m²

Knowledge Base & FAQ

A: "Nit" comes from Latin "nitere" (to shine) and was created as a simpler name for cd/m². Display manufacturers liked it because it's shorter to say! They're identical units - 1 nit = 1 cd/m² always.

A: It depends on ambient light!
• Dark room: 50-100 cd/m²
• Office: 200-300 cd/m²
• Sunny outdoors: 500-1000+ cd/m²
Your eyes adapt, so the same screen looks different in different lighting.

A: Not directly! Luminance measures perceived brightness by human eyes, which depends on color. Two lights with same luminance can use different power. You need efficiency data (lumens per watt) for energy calculations. Tools like our energy converter can help with related calculations once you have that data.
Accuracy & Educational Use

This tool uses industry-standard conversion factors that haven't changed in decades. The physics of light measurement is stable! All conversions are mathematically precise based on the definitions provided.

For students: Use this to check homework, understand relationships between units, and build intuition about brightness levels. The "Common Presets" give you real-world reference points.

Last updated: November 2025 - Conversion factors remain valid indefinitely as they're based on unit definitions, not measurements.

Educational content designed by science education specialists. Conversion logic remains unchanged for accuracy.

Quick Reference
Common Luminance Values
  • Starlight 0.001 cd/m²
  • Moonlight 0.1 cd/m²
  • Indoor lighting 100-500 cd/m²
  • Overcast sky 1,000 cd/m²
  • Full daylight 10,000 cd/m²
  • Sun's surface 1.6×10⁹ cd/m²
Display Standards
  • Cinema (DCI) 48 cd/m²
  • SDR TV 100-300 cd/m²
  • HDR TV 1000+ cd/m²
  • Smartphone 400-1000 cd/m²

For more specialized optical measurements, check our light intensity tools.

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