apostilbs (asb) to stilbs (sb) conversion

1 asb = 0.00003183099 sbsb → asb
Formula
1 asb = 0.00003183099 sb

Understanding apostilbs to stilbs Conversion

The apostilb (asb) is a metric luminance unit equal to 1/π cd/m², based on perfectly diffusing surfaces. The stilb (sb) is a CGS luminance unit equal to one candela per square centimetre, or 10,000 cd/m²—a very large unit suited to bright sources. Converting apostilbs to stilbs therefore spans a wide range and combines the 1/π diffuse factor with the metre-to-centimetre area scaling.

Conversion Formula

1 asb=3.18310×10−5 sb1\ \text{asb} = 3.18310 \times 10⁻⁵\ \text{sb}

To convert apostilbs to stilbs, multiply by this factor:

sb=asb×0.00003183099\text{sb} = \text{asb} \times 0.00003183099

Step-by-Step Example

Convert 25 apostilbs to stilbs.

sb=25×0.00003183099=0.000795775 sb\text{sb} = 25 \times 0.00003183099 = 0.000795775\ \text{sb}

How to Convert apostilbs to stilbs

Scale metric apostilb luminance down to CGS stilbs with one multiplication.

  1. Take the apostilb value: Begin with your luminance, for example 25 asb.
  2. Multiply by 0.00003183099: The apostilb-to-stilb factor.
  3. Read the result: 25 × 0.00003183099 = 0.000795775 stilbs.
  4. Reverse if needed: Multiply stilbs by 31415.93 to return to apostilbs.

apostilbs to stilbs conversion table

apostilbs (asb)stilbs (sb)
00
10.00003183099
20.00006366198
30.00009549297
40.000127324
50.0001591549
60.0001909859
70.0002228169
80.0002546479
90.0002864789
100.0003183099
150.0004774648
200.0006366198
250.0007957747
300.0009549297
400.00127324
500.001591549
600.001909859
700.002228169
800.002546479
900.002864789
1000.003183099
1500.004774648
2000.006366198
2500.007957747
3000.009549297
4000.0127324
5000.01591549
6000.01909859
7000.02228169
8000.02546479
9000.02864789
10000.03183099
20000.06366198
30000.09549297
40000.127324
50000.1591549
100000.3183099
250000.7957747
500001.591549
1000003.183099
2500007.957747
50000015.91549
100000031.83099

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.

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 apostilb?

One apostilb equals 0.00003183099 stilbs, since the stilb is candela per square centimetre (10,000 cd/m²) and the apostilb is 1/π cd/m².

How do I convert apostilbs to stilbs?

Multiply the apostilb value by 0.00003183099. For example, 10,000 apostilbs equals 10,000 × 0.00003183099 = 0.3183099 stilbs.

How do I convert stilbs back to apostilbs?

Multiply stilbs by 31415.93. So 0.01 stilbs equals about 314.16 apostilbs.

Why is the stilb such a large luminance unit?

The stilb is defined per square centimetre, so it represents intense luminance; the surface of a frosted incandescent bulb is only a few stilbs.

Where is the stilb used?

The stilb appears in older CGS-based optics and photometry literature for describing bright emitters, though cd/m² has largely replaced it.

People also convert

asb to cd/m2asb to ntasb to Lasb to fL

Complete apostilbs conversion table

asb
UnitResult
candelas per square metre (cd/m2)0.3183099 cd/m2
nits (nt)0.3183099 nt
stilbs (sb)0.00003183099 sb
lamberts (L)0.0001 L
foot-lamberts (fL)0.09290304 fL

Luminance conversions