stilbs (sb) to apostilbs (asb) conversion

1 sb = 31415.93 asbasb → sb
Formula
1 sb = 31415.93 asb

Understanding Stilbs to Apostilbs Conversion

The stilb (sb) is a CGS unit of luminance equal to one candela per square centimeter, historically used for very bright surfaces. The apostilb (asb) is a photometric luminance unit equal to 1/π candela per square meter, once common in lighting and ophthalmology for describing perceived brightness. Converting stilbs to apostilbs spans both a unit-area change (cm² to m²) and the π factor built into the apostilb definition.

Conversion Formula

1 sb=31415.9 asb1\ \text{sb} = 31415.9\ \text{asb}

To convert stilbs to apostilbs, multiply by this factor:

asb=sb×31415.93\text{asb} = \text{sb} \times 31415.93

Step-by-Step Example

Convert 25 stilbs to apostilbs.

asb=25×31415.93=785398 asb\text{asb} = 25 \times 31415.93 = 785398\ \text{asb}

How to Convert Stilbs to Apostilbs

Move between two legacy luminance units that differ by area scale and a π factor.

  1. Take the stilb value: For example, 25 sb.
  2. Multiply by 31415.93: This single factor covers the cm²-to-m² and π adjustments.
  3. Compute: 25×31415.93=78539825 \times 31415.93 = 785398.
  4. State the result: 25 stilbs equals about 785,398 asb.

stilbs to apostilbs conversion table

stilbs (sb)apostilbs (asb)
00
131415.93
262831.85
394247.78
4125663.7
5157079.6
6188495.6
7219911.5
8251327.4
9282743.3
10314159.3
15471238.9
20628318.5
25785398.2
30942477.8
401256637
501570796
601884956
702199115
802513274
902827433
1003141593
1504712389
2006283185
2507853982
3009424778
40012566370
50015707960
60018849560
70021991150
80025132740
90028274330
100031415930
200062831850
300094247780
4000125663700
5000157079600
10000314159300
25000785398200
500001570796000
1000003141593000
2500007853982000
50000015707960000
100000031415930000

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}.

What is the apostilb?

The apostilb is an obsolete unit of luminance once used to describe the brightness of diffusely reflecting or emitting surfaces. It belongs to a family of "1/π" luminance units designed to simplify calculations for perfectly diffuse (Lambertian) surfaces.

Definition

One apostilb is defined as one lumen per square metre emitted from a perfectly diffusing surface, which equals 1/π candela per square metre.

1 asb=0.318310 cd/m21\ \text{asb} = 0.318310\ \text{cd/m}^2

Exactly, 1 asb=1π cd/m2=10−4 lambert1\ \text{asb} = \frac{1}{\pi}\ \text{cd/m}^2 = 10⁻⁴\ \text{lambert}.

Origin and History

The apostilb was part of an early-20th-century set of photometric units (alongside the lambert and foot-lambert) built around the factor 1/π so that a Lambertian surface illuminated to a given number of lux would have a numerically equal luminance. The prefix "apo-" distinguished it from the stilb.

Law and Notable Facts

The apostilb is not an SI unit and is now essentially obsolete, replaced by the candela per square metre. Its defining convenience was that a perfect diffuser receiving an illuminance of one lux has a luminance of exactly one apostilb.

Real-World Examples and Conversions

  • A white matte surface at 1 lux illuminance: about 1 apostilb.
  • 1 asb=1π cd/m2≈0.318310 cd/m21\ \text{asb} = \frac{1}{\pi}\ \text{cd/m}^2 \approx 0.318310\ \text{cd/m}^2.
  • 1 cd/m2=π apostilbs≈3.14159 asb1\ \text{cd/m}^2 = \pi\ \text{apostilbs} \approx 3.14159\ \text{asb}.
  • 104 apostilbs=1 lambert≈3183.10 cd/m210⁴\ \text{apostilbs} = 1\ \text{lambert} \approx 3183.10\ \text{cd/m}^2.

Frequently Asked Questions

How many apostilbs equal one stilb?

One stilb equals 31,415.93 apostilbs, reflecting both the cm²-to-m² area change and the π factor in the apostilb.

How do I convert apostilbs back to stilbs?

Multiply the apostilb value by 0.00003183099. So 31,415.93 asb equals 1 sb.

Why does the factor contain π?

The apostilb is defined as (1/π) cd/m², so converting from a candela-per-area unit like the stilb introduces a factor of π.

Where were these luminance units used?

Both are legacy photometric units; the apostilb appeared in lighting engineering and vision science, while the stilb described very bright emitting surfaces.

What is 2 stilbs in apostilbs?

Multiply 2 by 31,415.93 to get 62,831.86 asb.

People also convert

sb to cd/m2sb to ntsb to Lsb to fL

Complete stilbs conversion table

sb
UnitResult
candelas per square metre (cd/m2)10000 cd/m2
nits (nt)10000 nt
apostilbs (asb)31415.93 asb
lamberts (L)3.141593 L
foot-lamberts (fL)2918.635 fL

Luminance conversions