Understanding nits to foot-lamberts Conversion
The nit (nt) is the SI luminance unit — one candela per square metre — used to specify the brightness of screens and displays. The foot-lambert (fL) is a US customary luminance unit defined as 1/π candela per square foot, long favoured in cinema projection and lighting design to describe screen brightness. Converting nits to foot-lamberts is essential when translating projector and display specifications between metric and US customary standards, such as the SMPTE recommendations for theatre screens.
Conversion Formula
To convert nits to foot-lamberts, multiply by this factor:
Step-by-Step Example
Convert 25 nits to foot-lamberts.
How to Convert nits to foot-lamberts
Convert metric display luminance into the foot-lamberts used in projection work.
- Take your luminance in nits: Start with the cd/m² (nit) value.
- Multiply by the factor: Multiply by 0.2918635, the number of foot-lamberts per nit.
- Report in foot-lamberts: The result is the equivalent luminance in fL.
- Worked result: 25 nt × 0.2918635 = 7.29659 fL.
nits to foot-lamberts conversion table
| nits (nt) | foot-lamberts (fL) |
|---|---|
| 0 | 0 |
| 1 | 0.2918635 |
| 2 | 0.583727 |
| 3 | 0.8755905 |
| 4 | 1.167454 |
| 5 | 1.459318 |
| 6 | 1.751181 |
| 7 | 2.043045 |
| 8 | 2.334908 |
| 9 | 2.626772 |
| 10 | 2.918635 |
| 15 | 4.377953 |
| 20 | 5.83727 |
| 25 | 7.296588 |
| 30 | 8.755905 |
| 40 | 11.67454 |
| 50 | 14.59318 |
| 60 | 17.51181 |
| 70 | 20.43045 |
| 80 | 23.34908 |
| 90 | 26.26772 |
| 100 | 29.18635 |
| 150 | 43.77953 |
| 200 | 58.3727 |
| 250 | 72.96588 |
| 300 | 87.55905 |
| 400 | 116.7454 |
| 500 | 145.9318 |
| 600 | 175.1181 |
| 700 | 204.3045 |
| 800 | 233.4908 |
| 900 | 262.6772 |
| 1000 | 291.8635 |
| 2000 | 583.727 |
| 3000 | 875.5905 |
| 4000 | 1167.454 |
| 5000 | 1459.318 |
| 10000 | 2918.635 |
| 25000 | 7296.588 |
| 50000 | 14593.18 |
| 100000 | 29186.35 |
| 250000 | 72965.88 |
| 500000 | 145931.8 |
| 1000000 | 291863.5 |
What is the nit?
The nit is a unit of luminance used to describe the brightness of light emitted from or reflected by a surface, most familiarly the screens of televisions, monitors, and phones. It is numerically identical to the SI unit, the candela per square metre.
Definition
One nit is exactly one candela per square metre, the luminous intensity of one candela spread over one square metre of projected surface area.
The two units are interchangeable: .
Origin and History
The name "nit" derives from the Latin nitere, meaning "to shine," and came into use in the mid-20th century as a convenient shorthand for the candela per square metre. It remains popular in the display and photometry industries.
Law and Notable Facts
The nit is not an official SI unit name but is exactly equal to the SI candela per square metre, so it carries no ambiguity. Display manufacturers routinely quote peak brightness in nits, with high-dynamic-range (HDR) televisions marketed at 1000 nits or more.
Real-World Examples and Conversions
- Standard SDR television: about 100 nits reference white.
- Modern OLED and LCD monitors: 250–600 nits.
- HDR displays: peak highlights of 1000–4000 nits.
- .
What is the Foot-Lambert?
The foot-lambert is a non-SI unit of luminance, expressing the brightness of a surface as seen by an observer. It remains widely used in the cinema, projection, and display industries in the United States, where screen brightness is often specified in foot-lamberts.
Definition
The foot-lambert is defined so that a perfectly diffusing (Lambertian) surface emitting or reflecting a total luminous flux of one lumen per square foot has a luminance of one foot-lambert.
Equivalently, . As with the lambert, the factor of arises from the cosine emission geometry of a Lambertian source. Because one square foot equals , the conversion follows directly: .
Origin and History
The foot-lambert is the imperial-unit counterpart of the lambert, both descending from Johann Heinrich Lambert's foundational photometry. It became entrenched in mid-20th-century American engineering practice, particularly in cinema, where SMPTE standards long specified projected picture brightness in foot-lamberts.
Law and Notable Facts
The foot-lambert is not an SI unit, but it persists in professional standards. SMPTE recommends an open-gate (unmodulated) screen luminance of 14 fL (≈ 48 cd/m²) for film projection and 16 fL peak white for digital cinema in a dark theater. HDR home displays, by contrast, target hundreds to over a thousand cd/m².
Real-World Examples and Conversions
- 14 foot-lamberts (SMPTE film reference) ≈ 47.97 cd/m².
- 1 foot-lambert ≈ 3.42626 cd/m² ≈ 0.001076 lambert.
- A typical office display of 250 cd/m² is about 73 foot-lamberts.
- 1 lambert ≈ 929.03 foot-lamberts.
Frequently Asked Questions
How many foot-lamberts is one nit?
One nit equals about 0.291864 foot-lamberts, so a display's cd/m² rating is a little under a third of its value in fL.
How do I convert nits to foot-lamberts?
Multiply the nit value by 0.2918635. For example, 48 nits × 0.2918635 ≈ 14.01 fL, the SMPTE target for cinema screen brightness.
How do I convert foot-lamberts back to nits?
Multiply the foot-lambert value by 3.426259. So 14 fL ≈ 47.97 nits.
Why do projectionists use foot-lamberts?
Foot-lamberts have been the standard for measuring reflected screen luminance in cinemas; the SMPTE reference of 14 fL (about 48 nits) defines proper open-gate projection brightness.
Does the π factor matter here?
Yes — the foot-lambert is 1/π cd/ft², so the nit-to-fL factor combines the π term with the foot-to-metre area conversion.
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Complete nits conversion table
| Unit | Result |
|---|---|
| candelas per square metre (cd/m2) | 1 cd/m2 |
| stilbs (sb) | 0.0001 sb |
| apostilbs (asb) | 3.141593 asb |
| lamberts (L) | 0.0003141593 L |
| foot-lamberts (fL) | 0.2918635 fL |