Luminance Converter
Inputs
| Candela per square metre | 250 cd/m² |
|---|
Luminance Converter
Convert between nits, cd/m², and foot-lamberts. Covers display brightness, cinema, photography, and lighting design.
SI / Common
Legacy Units
Luminance units
Luminance is the photometric measure of light emitted, transmitted, or reflected from a surface per unit area, per unit solid angle — in plain terms, it quantifies how bright a surface appears to an observer. The SI unit is candela per square metre (cd/m²), informally called the nit in the display industry. The two names are completely interchangeable: 1 nit = 1 cd/m².
Luminance differs from illuminance (lux), which measures light arriving at a surface. A photography studio lit to 1000 lx of illuminance will produce a range of luminance values depending on how reflective each object is; a white card reflects more, a dark backdrop reflects less.
Conversion reference
All conversions pivot on candela per square metre.
| Unit | cd/m² equivalent | Notes |
|---|---|---|
| 1 nit | 1 | Informal synonym for cd/m²; universal in consumer electronics |
| 1 foot-lambert (fL) | ≈ 3.4263 | (1/π) cd/ft²; common in US cinema projection specs |
The foot-lambert definition follows from the foot-candle: a Lambertian surface with 1 fc of illuminance reflects 1 fL of luminance if fully reflective (reflectance = 1). Because of the π factor in the Lambertian reflection formula, 1 fL ≠ 1 fc; instead, 1 fL ≈ 3.426 cd/m².
Where each unit appears
cd/m² is the formal SI unit used in engineering datasheets, IEC standards, and scientific publications. Display panel specifications from manufacturers almost always list peak and typical brightness in cd/m².
Nit is the working vocabulary of the consumer-electronics and streaming industries. "HDR1000" shorthand means the panel peaks at 1000 nits. Nit counts appear in phone reviews, TV comparisons, and streaming metadata formats such as HDR10 and Dolby Vision.
Foot-lambert remains in use in North American cinema. The Digital Cinema Initiatives (DCI) specification calls for 14 fL (≈ 48 cd/m²) at the screen for 2D presentations and 7 fL (≈ 24 cd/m²) for 3D, where polarised glasses absorb roughly half the light.
Typical luminance levels
| Source / application | Approximate luminance |
|---|---|
| Starlit sky | ~0.001 cd/m² |
| Moonlit scene | ~1 cd/m² |
| Laptop display (SDR typical) | 200–400 nits |
| HDR10 consumer TV peak | 1 000 nits |
| Dolby Vision cinema screen | ≈ 108 nits (31.5 fL) |
| DCI cinema 2D projector | ≈ 48 nits (14 fL) |
| Smartphone outdoor peak | 800–2 000 nits |
| Clear blue sky | ~8 000 cd/m² |
| Direct sunlight | ~1 000 000 000 cd/m² |
How to use this converter
Enter a value in any field and all other fields update instantly. To find a display's foot-lambert equivalent for a cinema spec, type the nit value in the Nit or cd/m² field and read off the Foot-lambert result. For the reverse — converting a projector spec in fL to nits — type in the Foot-lambert field instead.
Frequently Asked Questions (FAQ)
What is a nit, and is it the same as cd/m²?
Yes — a nit is exactly one candela per square metre (cd/m²). "Nit" is an informal name adopted by the display industry; the formal SI unit is cd/m². The two terms are completely interchangeable: 300 nits = 300 cd/m².
The word "nit" comes from the Latin nitere (to shine) and became common in consumer electronics specs because it is shorter than "candela per square metre." Standards bodies such as CIE and IEC still use cd/m² in formal documents.
How do I convert nits to foot-lamberts?
Multiply by 1/π and account for the ft² → m² area factor:
1 foot-lambert (fL) = (1/π) cd/ft² = (1/π) / 0.09290304 cd/m² ≈ 3.4263 cd/m²
To convert:
- nits → fL: divide by 3.4263 (e.g. 100 nits ÷ 3.4263 ≈ 29.2 fL)
- fL → nits: multiply by 3.4263 (e.g. 16 fL × 3.4263 ≈ 54.8 nits)
Foot-lamberts appear in cinema projection standards (DCI specifies 14 fL ≈ 48 nits for 2D screens) and older US broadcast equipment. Most modern display specifications use nits or cd/m².
What luminance levels are used in displays and cinema?
Typical luminance targets by application:
- Smartphone outdoor readable: 800–2 000 nits
- PC/laptop display (SDR): 200–400 nits
- HDR10 peak (consumer TVs): 1000 nits
- Dolby Vision peak: up to 4000–10 000 nits
- DCI cinema 2D (projector): 14 fL ≈ 48 nits
- DCI cinema 3D (projector): 7 fL ≈ 24 nits (half lost through polarised glasses)
- HDR projector (home): 150–300 nits
- Direct sunlight: ~1 000 000 000 nits (10⁹ cd/m²)
The human eye can perceive comfortable contrasts over roughly 0.001–10 000 nits in typical viewing conditions.
What is the difference between luminance and illuminance?
Luminance and illuminance are related but describe different things:
Luminance (cd/m², nit) measures the light emitted or reflected from a surface toward the observer — it describes how bright a surface appears. A monitor displaying white, a cinema screen, and a lamp shade all have measurable luminance.
Illuminance (lux, foot-candle) measures the light incident on a surface — how much light falls on a desk, a floor, or a photography subject. A bright studio might be lit to 2000 lx, but the luminance of the objects depends on how reflective they are.
The relationship: Illuminance (lux) × reflectance factor ÷ π ≈ luminance (cd/m²) for diffuse (Lambertian) surfaces. This is why an illuminance meter and a luminance meter read in different units even when pointed at the same surface.
Disclaimer
1 nit = 1 cd/m² (exact). 1 foot-lambert = (1/π) cd/ft² ≈ 3.426259 cd/m² (exact: 1/(π × 0.09290304)).