foot-lamberts (fL) to nits (nt) conversion

1 fL = 3.426259 ntnt → fL
Formula
1 fL = 3.426259 nt

Understanding foot-lamberts to nits Conversion

A foot-lambert (fL) is a US customary luminance unit used to specify projector and cinema screen brightness. A nit (nt) is the common name for the candela per square metre, the SI luminance unit used on television, monitor, and smartphone datasheets. Converting foot-lamberts to nits is a frequent task for AV professionals matching US projection specs against display brightness ratings.

Conversion Formula

1 fL=3.42626 nt1\ \text{fL} = 3.42626\ \text{nt}

To convert foot-lamberts to nits, multiply by this factor:

nt=fL×3.426259\text{nt} = \text{fL} \times 3.426259

Step-by-Step Example

Convert 25 foot-lamberts to nits.

nt=25×3.426259=85.6565 nt\text{nt} = 25 \times 3.426259 = 85.6565\ \text{nt}

How to Convert foot-lamberts to nits

Match US projection brightness to a display's nit rating with one multiplication.

  1. Note the factor: One foot-lambert equals 3.426259 nits.
  2. Take your luminance in foot-lamberts: Begin with the value to convert, such as 25 fL.
  3. Multiply: Multiply the foot-lambert value by 3.426259.
  4. Read the result: 25×3.426259=85.656525 \times 3.426259 = 85.6565 nits.

foot-lamberts to nits conversion table

foot-lamberts (fL)nits (nt)
00
13.426259
26.852518
310.27878
413.70504
517.1313
620.55755
723.98381
827.41007
930.83633
1034.26259
1551.39389
2068.52518
2585.65648
30102.7878
40137.0504
50171.313
60205.5755
70239.8381
80274.1007
90308.3633
100342.6259
150513.9389
200685.2518
250856.5648
3001027.878
4001370.504
5001713.13
6002055.755
7002398.381
8002741.007
9003083.633
10003426.259
20006852.518
300010278.78
400013705.04
500017131.3
1000034262.59
2500085656.48
50000171313
100000342625.9
250000856564.8
5000001713130
10000003426259

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.

1 fL=3.42626 cd/m21\ \text{fL} = 3.42626\ \text{cd/m}^2

Equivalently, 1 fL=1π cd/ft21\ \text{fL} = \frac{1}{\pi}\ \text{cd/ft}^2. As with the lambert, the factor of π\pi arises from the cosine emission geometry of a Lambertian source. Because one square foot equals 0.09290304 m20.09290304\ \text{m}^2, the conversion follows directly: 1π×0.09290304 cd/m2=3.42626 cd/m2\frac{1}{\pi \times 0.09290304}\ \text{cd/m}^2 = 3.42626\ \text{cd/m}^2.

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.

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.

1 nt=1 cd/m21\ \text{nt} = 1\ \text{cd/m}^2

The two units are interchangeable: 1 nt=1 cd/m2=1 lm/(m2⋅sr)1\ \text{nt} = 1\ \text{cd/m}^2 = 1\ \text{lm}/(\text{m}^2 \cdot \text{sr}).

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.
  • 1 nt=1 cd/m2=10−4 stilb≈3.14159 apostilbs1\ \text{nt} = 1\ \text{cd/m}^2 = 10⁻⁴\ \text{stilb} \approx 3.14159\ \text{apostilbs}.

Frequently Asked Questions

How many nits are in one foot-lambert?

One foot-lambert equals about 3.42626 nits, because a nit is defined as one candela per square metre.

Is a nit the same as a candela per square metre?

Yes, "nit" is simply the everyday name for the candela per square metre, so this conversion is identical to converting foot-lamberts to cd/m².

Why do AV installers care about this conversion?

Projector brightness for home theatre and cinema is often quoted in foot-lamberts, while flat-panel displays list nits, so installers convert to compare and match brightness targets.

What is a typical target brightness in nits?

Home-theatre projection often aims for about 16 fL (roughly 55 nits), while HDR displays can exceed 1,000 nits for highlight detail.

How do I convert 50 foot-lamberts to nits?

Multiply 50 by 3.426259 to get about 171.313 nits.

People also convert

fL to cd/m2fL to sbfL to asbfL to L

Complete foot-lamberts conversion table

fL
UnitResult
candelas per square metre (cd/m2)3.426259 cd/m2
nits (nt)3.426259 nt
stilbs (sb)0.0003426259 sb
apostilbs (asb)10.76391 asb
lamberts (L)0.001076391 L

Luminance conversions