Convert Apostilbs to Watts per Square Centimeter per Steradian (at 555 nm)
Apostilb (asb) to Watt per Square Centimeter per Steradian (at 555 nm) (W/cm²/sr) luminance conversion — enter any value below to get an instant result, or use the table for common values.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 asb = 4.66047E-08 W/cm²/sr
1 Apostilb = 4.66047E-08 Watts per Square Centimeter per Steradian (at 555 nm)
1 Watt per Square Centimeter per Steradian (at 555 nm) = 21457078 Apostilbs
1 asb in every supported unit
Conversion chart: Apostilb to Watts per Square Centimeter per Steradian (at 555 nm)
Conversion table
| Apostilb (asb) | Watt per Square Centimeter per Steradian (at 555 nm) (W/cm²/sr) |
|---|---|
| 0.01 asb | 4.66047E-10 W/cm²/sr |
| 0.1 asb | 4.66047E-09 W/cm²/sr |
| 1 asb | 4.66047E-08 W/cm²/sr |
| 2 asb | 9.32093E-08 W/cm²/sr |
| 3 asb | 1.39814E-07 W/cm²/sr |
| 5 asb | 2.33023E-07 W/cm²/sr |
| 10 asb | 4.66047E-07 W/cm²/sr |
| 20 asb | 9.32093E-07 W/cm²/sr |
| 50 asb | 2.33023E-06 W/cm²/sr |
| 100 asb | 4.66047E-06 W/cm²/sr |
| 1000 asb | 4.66047E-05 W/cm²/sr |
Apostilb (asb)
Definition: A CGS-system luminance unit defined so that a perfectly diffusing surface illuminated at one lux has a luminance of one apostilb — related to the lambert by a factor of 10,000.
History: Introduced in early 20th-century European photometry (the name from Greek "apo-" plus "stilb") as a more conveniently scaled alternative to the stilb for typical illuminated, rather than self-luminous, surfaces.
Current use: Still used in some European ophthalmology and vision science literature, particularly in perimetry equipment that measures visual field sensitivity in apostilbs.
Watt per Square Centimeter per Steradian (at 555 nm) (W/cm²/sr)
Definition: A radiometric luminance unit expressing radiant power per unit area per unit solid angle at 555 nanometers — the wavelength of peak human eye sensitivity — used to convert directly between physical radiant power and perceived brightness.
History: Defined using the luminous efficacy constant (683 lumens per watt at 555 nm, the photopic peak of human vision) that bridges radiometry (physical energy) and photometry (perceived brightness) at the single wavelength where the eye is most sensitive.
Current use: Used in laser safety calculations, optical radiometry, and calibration work where a source's physical radiant power must be related precisely to its perceived luminance.
Supported Units
| Unit | Symbol | In cd/m² |
|---|---|---|
| Candela per Square Meter | cd/m² | 1 cd/m² |
| Candela per Square Centimeter | cd/cm² | 10000 cd/m² |
| Candela per Square Foot | cd/ft² | 10.76391 cd/m² |
| Candela per Square Inch | cd/in² | 1550.0031 cd/m² |
| Kilocandela per Square Meter | kcd/m² | 1000 cd/m² |
| Stilb | sb | 10000 cd/m² |
| Lumen per Square Meter per Steradian | lm/m²/sr | 1 cd/m² |
| Lumen per Square Centimeter per Steradian | lm/cm²/sr | 10000 cd/m² |
| Lumen per Square Foot per Steradian | lm/ft²/sr | 10.76391 cd/m² |
| Watt per Square Centimeter per Steradian (at 555 nm) | W/cm²/sr | 6830000 cd/m² |
| Nit | nt | 1 cd/m² |
| Millinit | mnt | 0.001 cd/m² |
| Lambert | L | 3183.0989 cd/m² |
| Millilambert | mL | 3.1830989 cd/m² |
| Foot-Lambert | fL | 3.4262591 cd/m² |
| Apostilb | asb | 0.31830989 cd/m² |
| Blondel | bd | 0.31830989 cd/m² |
| Bril | bril | 3.1831E-08 cd/m² |
| Skot | sk | 0.0003183099 cd/m² |
About These Parameters
- Value
- The luminance value you want to convert, expressed in the "From" unit. Accepts decimals, so you can enter anything from a faint scotopic reading in skots to a display's rated brightness in nits.
- From Unit
- The unit your input value is currently measured in — a monitor spec sheet's nits, a cinema calibration report's foot-lamberts, or a scientific instrument's candela per square meter.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly and compare figures across display, cinema, and scientific contexts.
How Luminance Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to candela per square meter. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Apostilb → Watt per Square Centimeter per Steradian (at 555 nm): multiply by 4.66047E-08. For example, 1 asb × 4.66047E-08 = 4.66047E-08 W/cm²/sr.
Nits vs. Candela per Square Meter
A nit and a candela per square meter are exactly the same physical quantity — "nit" is simply the shorter, everyday name adopted by the display and consumer electronics industry. When a phone, TV, or monitor spec sheet quotes "1,000 nits," that number is identical to 1,000 cd/m² in a scientific paper. The two names exist for context, not physics: engineers and physicists tend to write cd/m², while marketing copy, review sites, and display datasheets almost universally write nits.
CGS vs. SI Luminance Units
Several units on this page — the stilb, lambert, apostilb, blondel, bril, and skot — predate the modern SI system and come from the centimeter-gram-second (CGS) system of photometric units used in early 20th-century physics. They were built around the idea of a perfectly diffusing ("Lambertian") surface rather than the candela directly, which is why their conversion factors to cd/m² involve π-related constants (a lambert, for instance, equals 1/π candela per square centimeter). Most of these CGS units have been superseded by candela-per-square-meter and its nit alias in modern engineering, but they still surface in legacy scientific literature, older photometric instruments, and specialized fields like vision research that never fully migrated to SI.
Example
A luminance of 1 asb equals 4.66047E-08 W/cm²/sr. For scale, a typical smartphone screen runs around 500-1,000 nits, a calibrated cinema screen is set to roughly 14-16 foot-lamberts, an overcast sky reads around 2,000-4,000 cd/m², and the full moon's surface luminance is only about 2,500 cd/m² despite looking far brighter against a dark night sky.
Frequently Asked Questions
How many Watts per Square Centimeter per Steradian (at 555 nm) are in 1 Apostilb?
1 Apostilb (asb) equals exactly 4.66047E-08 Watts per Square Centimeter per Steradian (at 555 nm) (W/cm²/sr).
What's the difference between luminance and brightness?
Luminance is the objective, physically measured quantity — candela per square meter, or nits — while "brightness" is often used loosely to describe the subjective perception of how light a surface looks, which also depends on surrounding contrast and the viewer's eye adaptation. Luminance is what a light meter measures; brightness is what a person reports seeing.
Is a nit the same as a candela per square meter?
Yes — a nit and a candela per square meter (cd/m²) are exactly the same unit under two different names. "Nit" is the informal name used throughout the display and consumer electronics industry, while cd/m² is the formal SI name used in scientific and engineering contexts.
Why do cinema screens use foot-lamberts instead of nits?
The film and projection industry standardized on foot-lamberts decades before nits became common in consumer electronics, and SMPTE calibration standards for theatrical and home-theater screens (typically 14-16 foot-lamberts) are still written in that unit today. Converting to nits (1 fL ≈ 3.43 cd/m²) shows that cinema screens are actually much dimmer than a modern smartphone or TV display, which is intentional for a dark viewing room.
Why are there so many old CGS luminance units like the stilb and apostilb?
Before the SI system standardized photometry around the candela and candela-per-square-meter in the mid-20th century, different countries and scientific traditions developed their own luminance units within the centimeter-gram-second (CGS) system — the stilb and lambert in general use, the apostilb and its French-system twin the blondel for illuminated surfaces, and the extremely small bril and skot for vision research into low-light perception. Most have fallen out of everyday use but still appear in older instruments, legacy literature, and specialized scientific fields.
How accurate are these conversions?
Every conversion factor used here is the exact, internationally recognized relationship between the underlying luminance units — results are limited only by floating-point display precision, not by rounded conversion constants.