foot-lamberts (fL) to stilbs (sb) conversion

1 fL = 0.0003426259 sbsb → fL
Formula
1 fL = 0.0003426259 sb

Understanding foot-lamberts to stilbs Conversion

A foot-lambert (fL) is a US customary unit of luminance used in projection and display work. A stilb (sb) is a CGS luminance unit equal to one candela per square centimetre, a very large value that makes it suited to describing intensely bright sources. Converting foot-lamberts to stilbs bridges the imperial luminance scale and the CGS system used in older optics literature.

Conversion Formula

1 fL=0.000342626 sb1\ \text{fL} = 0.000342626\ \text{sb}

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

sb=fL×0.0003426259\text{sb} = \text{fL} \times 0.0003426259

Step-by-Step Example

Convert 25 foot-lamberts to stilbs.

sb=25×0.0003426259=0.00856565 sb\text{sb} = 25 \times 0.0003426259 = 0.00856565\ \text{sb}

How to Convert foot-lamberts to stilbs

Bridge the imperial and CGS luminance units with a single multiplication.

  1. Note the factor: One foot-lambert equals 0.0003426259 stilbs.
  2. Take your luminance in foot-lamberts: Start with the value to convert, for example 25 fL.
  3. Multiply: Multiply the foot-lambert value by 0.0003426259.
  4. Read the result: 25×0.0003426259=0.0085656525 \times 0.0003426259 = 0.00856565 stilbs.

foot-lamberts to stilbs conversion table

foot-lamberts (fL)stilbs (sb)
00
10.0003426259
20.0006852518
30.001027878
40.001370504
50.00171313
60.002055755
70.002398381
80.002741007
90.003083633
100.003426259
150.005139389
200.006852518
250.008565648
300.01027878
400.01370504
500.0171313
600.02055755
700.02398381
800.02741007
900.03083633
1000.03426259
1500.05139389
2000.06852518
2500.08565648
3000.1027878
4000.1370504
5000.171313
6000.2055755
7000.2398381
8000.2741007
9000.3083633
10000.3426259
20000.6852518
30001.027878
40001.370504
50001.71313
100003.426259
250008.565648
5000017.1313
10000034.26259
25000085.65648
500000171.313
1000000342.6259

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 stilb?

The stilb is a CGS unit of luminance, describing the brightness of a surface in terms of luminous intensity per unit area. It was widely used in older photometric literature before the SI candela per square metre became standard.

Definition

One stilb is one candela per square centimetre. Since there are ten thousand square centimetres in a square metre, the stilb is a large unit relative to the SI luminance unit.

1 sb=10000 cd/m21\ \text{sb} = 10000\ \text{cd/m}^2

Exactly, 1 sb=1 cd/cm2=104 cd/m2=104 nits1\ \text{sb} = 1\ \text{cd/cm}^2 = 10⁴\ \text{cd/m}^2 = 10⁴\ \text{nits}.

Origin and History

The stilb was introduced by the French physicist André Blondel around 1920, its name taken from the Greek stilbein, "to glitter." It belonged to the centimetre–gram–second system and was used chiefly in continental Europe.

Law and Notable Facts

The stilb is not part of the SI and has largely fallen out of use in favour of the candela per square metre. Because it references the square centimetre, a single stilb represents a very bright surface: the sun's disc at the horizon is on the order of a few hundred stilbs.

Real-World Examples and Conversions

  • A frosted incandescent lamp surface: a few stilbs.
  • The sun's disc viewed from Earth: roughly 160,000 cd/m², or about 16 stilbs.
  • 1 sb=104 cd/m2=104 nits1\ \text{sb} = 10⁴\ \text{cd/m}^2 = 10⁴\ \text{nits}.
  • 1 cd/m2=10−4 sb1\ \text{cd/m}^2 = 10⁻⁴\ \text{sb}.

Frequently Asked Questions

How many stilbs are in one foot-lambert?

One foot-lambert equals about 0.000342626 stilbs, because the stilb is a very large CGS luminance unit.

How many foot-lamberts make one stilb?

About 2918.64 foot-lamberts equal one stilb, since a stilb is one candela per square centimetre.

What is a stilb typically used for?

The stilb appears in older optics and photometry texts for describing very bright surfaces such as filament lamps; it is 10,000 nits per unit and rarely used today.

How does the stilb relate to the nit?

One stilb equals exactly 10,000 nits (candelas per square metre), reflecting the factor between square centimetres and square metres.

How do I convert 500 foot-lamberts to stilbs?

Multiply 500 by 0.0003426259 to get about 0.171313 stilbs.

People also convert

fL to cd/m2fL to ntfL 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