Luminance Converter
ScienceConvert luminance units instantly — candela per square metre, nit, foot-lambert, lambert, and stilb. Used in display engineering, lighting design, and photography.
From
To
All conversionsfor 1 Nit (nt) — same as cd/m²
| Candela/metre² (cd/m²) | 1 |
| Nit (nt) — same as cd/m² | 1 |
| Millicandela/metre² (mcd/m²) | 1000 |
| Kilocandela/metre² (kcd/m²) | 0.001 |
| Candela/foot² (cd/ft²) | 0.092903044 |
| Foot-lambert (fL) | 0.29186352 |
| Lambert (L) | 0.00031415927 |
| Millilambert (mL) | 0.31415927 |
| Stilb (sb) | 0.0001 |
| Apostilb (asb) | 3.1415915 |
What is a Luminance?
A Luminance Converter translates between the measurement units used to quantify the brightness of a surface as perceived by an observer. Luminance is the photometric equivalent of radiance — it measures light emitted, reflected, or transmitted from a surface per unit area per unit solid angle. The SI unit is candela per square metre (cd/m²), also known by the trade term nit.
Luminance is essential in display technology, cinema, architectural lighting, photography, and vision science. Different industries favour different units: the display industry uses nits (cd/m²); cinema uses foot-lamberts (fL); older lighting research uses lamberts (L) or stilbs (sb) from the CGS system; and imperial engineering uses candela per square foot (cd/ft²).
The converter covers 10 units:
- SI: cd/m², nit (identical), mcd/m², kcd/m²
- Imperial: cd/ft², foot-lambert (fL)
- CGS: lambert (L), millilambert (mL), stilb (sb), apostilb (asb)
For illuminance (lux, foot-candle — light falling on a surface), use the Illumination Converter. For power output of light sources, use the Power Converter.
How to use this Luminance calculator
- Enter the luminance value in the From field.
- Select the From unit (e.g. nit or cd/m²).
- Select the To unit (e.g. foot-lambert).
- The converted value appears instantly.
- View the reference table for all unit conversions at once.
- Click ⇄ to reverse the direction.
Formula & Methodology
Base unit: cd/m² | Unit | cd/m² equivalent | |---|---| | cd/m² | 1 | | nit | 1 | | mcd/m² | 0.001 | | kcd/m² | 1,000 | | cd/ft² | 10.7639 | | fL | 3.426259 | | L (lambert) | 3,183.099 (= 10,000/π) | | mL | 3.183099 | | sb (stilb) | 10,000 | | asb (apostilb) | 0.318310 (= 1/π) | Worked example: Convert 400 nit to fL (for cinema comparison). - 400 cd/m² ÷ 3.426259 = 116.7 fL — far brighter than the 14 fL DCI standard for cinema. Common reference values: | Context | Luminance | |---|---| | DCI cinema screen | 14 fL ≈ 48 cd/m² | | SDR monitor (calibrated) | 80–120 cd/m² | | Typical smartphone | 400–800 nit | | HDR TV peak | 1,000–2,000 nit |
Frequently Asked Questions
What is luminance and how is it measured?
Luminance is the amount of light emitted or reflected from a surface per unit area in a given direction, measured from the observer's perspective. It is the physical quantity corresponding to perceived brightness. The SI unit is candela per square metre (cd/m²), also called the nit. A typical computer monitor has a luminance of 200–400 nit, while the sun is approximately 1.6 × 10⁹ cd/m².
What is a nit and how does it relate to cd/m²?
A nit is simply another name for candela per square metre (cd/m²). The two are identical: 1 nit = 1 cd/m². 'Nit' is used informally in the display industry, while cd/m² is the formal SI unit used in scientific and engineering contexts. Display brightness specifications (for monitors, TVs, and smartphones) are almost always given in nits.
What luminance does a typical smartphone screen have?
Consumer smartphone screens typically achieve 400–800 nit for standard content. High-brightness outdoor mode on flagship devices can reach 1,500–2,000 nit for HDR peak highlights. Minimum comfortable outdoor readability in direct sunlight requires approximately 600–700 nit. Comparing two devices requires both devices to be measured under the same conditions.
What is a foot-lambert (fL)?
A foot-lambert (fL) is a unit of luminance used in the cinema and projection industry in the US. It equals approximately 3.426 cd/m². Digital cinema projectors are calibrated to a screen luminance of 14 fL (approximately 48 cd/m²), as specified by DCI (Digital Cinema Initiatives). Older cinema projectors targeting analogue standards used 16 fL.
What is the difference between luminance and illuminance?
Luminance (cd/m²) describes how bright a surface appears — it is emitted or reflected light per unit area from the observer's perspective. Illuminance (lux, lx) describes how much light falls on a surface per unit area. A white wall illuminated at 1,000 lux will have a higher luminance than a black wall under the same illumination. They measure different things: illuminance is about the light source and surface, luminance is about what the eye sees.
What is a stilb?
A stilb (sb) is the CGS unit of luminance, equal to 1 candela per square centimetre, which equals 10,000 cd/m². It is rarely used today outside historical scientific literature. It reflects the CGS system's use of centimetres rather than metres as the base length unit.
What is a lambert (L)?
A lambert is a CGS unit of luminance defined as 1/π candela per square centimetre, approximately 3,183 cd/m². It was commonly used in early photometric measurements but has been superseded by cd/m² in modern practice. The related apostilb (asb) is 1/π cd/m², approximately 0.318 cd/m².
What luminance should a monitor be set to for colour-accurate work?
For professional colour-grading and photo editing, the standard monitor luminance target is 80–120 cd/m² in a dim viewing environment. Video mastering for SDR typically uses 100 cd/m². HDR mastering targets range from 400 cd/m² (HDR400) to 10,000 cd/m² (reference HDR). Lower luminance reduces eye strain in dark environments.
Does luminance affect photography exposure calculations?
Yes. Camera exposure is fundamentally a measure of how much luminance is reaching the sensor from the scene. The relationship between luminance (L), aperture (N), shutter speed (t), and ISO (S) is: L = N² / (t × S × K), where K is a camera calibration constant (~12.5). Understanding luminance values helps explain why high-key scenes need more exposure compensation.
What is the luminance of common light sources?
Approximate luminance values: clear sky (daytime) ~8,000 cd/m², overcast sky ~2,000 cd/m², full moon ~2,500 cd/m², candle flame ~10,000 cd/m², standard fluorescent tube ~5,000–8,000 cd/m², reading lamp at 1 m distance (as seen from the source) varies widely. The sun at noon is approximately 1.6 × 10⁹ cd/m².