lamberts (L) to stilbs (sb) conversion

1 L = 0.3183099 sbsb → L
Formula
1 L = 0.3183099 sb

Understanding Lamberts to Stilbs Conversion

The lambert (L) is a CGS luminance unit for a perfectly diffusing surface emitting 1 lumen per square centimetre. The stilb (sb) is another CGS luminance unit, defined directly as 1 candela per square centimetre, historically used in European optics and photometry. Because both share the square-centimetre basis but differ by whether the definition is lumen- or candela-based, converting lamberts to stilbs simply removes a factor of π\pi, a relationship that appears in classical illumination theory.

Conversion Formula

1 L=0.318310 sb1\ \text{L} = 0.318310\ \text{sb}

To convert Lamberts to Stilbs, multiply by this factor:

sb=L×0.3183099\text{sb} = \text{L} \times 0.3183099

Step-by-Step Example

Convert 25 Lamberts to Stilbs.

sb=25×0.3183099=7.95775 sb\text{sb} = 25 \times 0.3183099 = 7.95775\ \text{sb}

How to Convert Lamberts to Stilbs

Both are CGS luminance units, so the conversion is a single multiplication by 1/π1/\pi.

  1. Take the lambert value: record the luminance in L.
  2. Multiply by 0.3183099: this factor is 1/π1/\pi and yields stilbs.
  3. Calculate: for 25 L, compute 25×0.318309925 \times 0.3183099.
  4. Report the result: the luminance is 7.95775 sb.

lamberts to stilbs conversion table

lamberts (L)stilbs (sb)
00
10.3183099
20.6366198
30.9549297
41.27324
51.591549
61.909859
72.228169
82.546479
92.864789
103.183099
154.774648
206.366198
257.957747
309.549297
4012.7324
5015.91549
6019.09859
7022.28169
8025.46479
9028.64789
10031.83099
15047.74648
20063.66198
25079.57747
30095.49297
400127.324
500159.1549
600190.9859
700222.8169
800254.6479
900286.4789
1000318.3099
2000636.6198
3000954.9297
40001273.24
50001591.549
100003183.099
250007957.747
5000015915.49
10000031830.99
25000079577.47
500000159154.9
1000000318309.9

What is the Lambert?

The lambert is a non-SI unit of luminance, describing how much light is emitted or reflected from a surface toward an observer. It is named after the Swiss-German polymath Johann Heinrich Lambert and appears mainly in older optics, photometry, and lighting literature.

Definition

The lambert is defined so that a perfectly diffusing (Lambertian) surface emitting or reflecting a total luminous flux of one lumen per square centimetre has a luminance of one lambert.

1 L=3183.10 cd/m21\ \text{L} = 3183.10\ \text{cd/m}^2

Equivalently, 1 L=1π cd/cm2=104π cd/m21\ \text{L} = \frac{1}{\pi}\ \text{cd/cm}^2 = \frac{10⁴{\pi}\ \text{cd/m}^2. The factor of π\pi enters because luminance in candela per unit area relates to the emitted lumens per unit area through the geometry of a Lambertian (cosine-law) emitter. Sub-multiples such as the millilambert (mL) and microlambert are common in practice.

Origin and History

The unit honors Johann Heinrich Lambert (1728–1777), whose 1760 work Photometria laid the mathematical foundations of photometry, including the cosine emission law of diffuse surfaces. The lambert itself was proposed in the early 20th century as photometry was being systematized, and it saw wide use before the SI candela-per-square-metre (nit) became standard.

Law and Notable Facts

The lambert is not part of the SI and is discouraged in modern metrology, but it survives in legacy instruments and texts. A key convenience of the lambert family is that a perfect diffuse reflector illuminated by one lux has a luminance of exactly 1π×10−4\tfrac{1}{\pi}\times10^{-4} lambert, tidily linking illuminance and luminance for ideal surfaces.

Real-World Examples and Conversions

  • A surface of 1 lambert equals about 3183 cd/m², roughly the brightness of a bright fluorescent lamp diffuser.
  • 1 millilambert = 3.18310 cd/m², close to comfortable indoor lighting levels.
  • The closely related foot-lambert (used for cinema screens) equals about 3.426 cd/m²; standard theater screen luminance of 14 fL corresponds to roughly 48 cd/m².
  • 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 lambert?

One lambert equals 0.3183099 stilbs, which is exactly 1/π1/\pi because the lambert's lumen-based definition differs from the stilb's candela-based one by that factor.

How do I convert lamberts to stilbs?

Multiply the lambert value by 0.3183099. For example, 4 L equals about 1.27324 sb.

Why is the factor equal to 1 over pi?

A Lambertian surface radiates over a hemisphere, so relating its lumen-per-area luminance (lambert) to a candela-per-area luminance (stilb) introduces the 1/π1/\pi factor.

What is a stilb used for?

The stilb is an older CGS unit for very high luminances, once common in European optics and lamp measurements before the SI cd/m² became standard.

How do I convert stilbs back to lamberts?

Multiply the stilb value by 3.141593, which is π\pi.

People also convert

L to cd/m2L to ntL to asbL to fL

Complete lamberts conversion table

L
UnitResult
candelas per square metre (cd/m2)3183.099 cd/m2
nits (nt)3183.099 nt
stilbs (sb)0.3183099 sb
apostilbs (asb)10000 asb
foot-lamberts (fL)929.0304 fL

Luminance conversions