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Convert Watts per Square Centimeter per Steradian (at 555 nm) to Stilbs

Watt per Square Centimeter per Steradian (at 555 nm) (W/cm²/sr) to Stilb (sb) 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.

The numeric value you want to convert. Decimals are accepted.

Result

1 W/cm²/sr = 683 sb

1 Watt per Square Centimeter per Steradian (at 555 nm) = 683 Stilbs

1 Stilb = 0.0014641288 Watts per Square Centimeter per Steradian (at 555 nm)

1 W/cm²/sr in every supported unit

Conversion chart: Watt per Square Centimeter per Steradian (at 555 nm) to Stilbs

Conversion table

Watt per Square Centimeter per Steradian (at 555 nm) (W/cm²/sr) Stilb (sb)
0.01 W/cm²/sr 6.83 sb
0.1 W/cm²/sr 68.3 sb
1 W/cm²/sr 683 sb
2 W/cm²/sr 1366 sb
3 W/cm²/sr 2049 sb
5 W/cm²/sr 3415 sb
10 W/cm²/sr 6830 sb
20 W/cm²/sr 13660 sb
50 W/cm²/sr 34150 sb
100 W/cm²/sr 68300 sb
1000 W/cm²/sr 683000 sb

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.

Stilb (sb)

Definition: A CGS-system luminance unit equal to one candela per square centimeter, making it numerically identical to that unit but treated historically as its own named unit.

History: Introduced in the early 20th century as part of the centimeter-gram-second (CGS) system of photometric units, before the SI system standardized on candela per square meter as the base luminance unit.

Current use: Now largely obsolete in everyday use but still occasionally encountered in older European scientific literature and legacy photometric instrumentation calibrated to the CGS system.

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 Watt per Square Centimeter per Steradian (at 555 nm) → Stilb: multiply by 683. For example, 1 W/cm²/sr × 683 = 683 sb.

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 W/cm²/sr equals 683 sb. 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 Stilbs are in 1 Watt per Square Centimeter per Steradian (at 555 nm)?

1 Watt per Square Centimeter per Steradian (at 555 nm) (W/cm²/sr) equals exactly 683 Stilbs (sb).

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.

Convert Watt per Square Centimeter per Steradian (at 555 nm) to Other Luminance Units

Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Meter Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Centimeter Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Foot Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Inch Watt per Square Centimeter per Steradian (at 555 nm) to Kilocandela per Square Meter Watt per Square Centimeter per Steradian (at 555 nm) to Stilbs Watt per Square Centimeter per Steradian (at 555 nm) to Lumens per Square Meter per Steradian Watt per Square Centimeter per Steradian (at 555 nm) to Lumens per Square Centimeter per Steradian Watt per Square Centimeter per Steradian (at 555 nm) to Lumens per Square Foot per Steradian Watt per Square Centimeter per Steradian (at 555 nm) to Nits Watt per Square Centimeter per Steradian (at 555 nm) to Millinits Watt per Square Centimeter per Steradian (at 555 nm) to Lamberts Watt per Square Centimeter per Steradian (at 555 nm) to Millilamberts Watt per Square Centimeter per Steradian (at 555 nm) to Foot-Lamberts Watt per Square Centimeter per Steradian (at 555 nm) to Apostilbs Watt per Square Centimeter per Steradian (at 555 nm) to Blondels Watt per Square Centimeter per Steradian (at 555 nm) to Brils Watt per Square Centimeter per Steradian (at 555 nm) to Skots

Possible Luminance Conversions

Blondel to Candela per Square Foot Skot to Candela per Square Centimeter Lumen per Square Centimeter per Steradian to Watts per Square Centimeter per Steradian (at 555 nm) Millinit to Stilbs Candela per Square Meter to Brils Millinit to Kilocandela per Square Meter Candela per Square Centimeter to Millilamberts Lumen per Square Centimeter per Steradian to Stilbs Blondel to Candela per Square Centimeter Lumen per Square Meter per Steradian to Candela per Square Centimeter Lambert to Stilbs Nit to Foot-Lamberts Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Meter Lumen per Square Foot per Steradian to Millilamberts Foot-Lambert to Millinits Apostilb to Millinits Kilocandela per Square Meter to Lamberts Blondel to Millilamberts Lumen per Square Foot per Steradian to Foot-Lamberts Nit to Blondels Skot to Watts per Square Centimeter per Steradian (at 555 nm) Lumen per Square Foot per Steradian to Watts per Square Centimeter per Steradian (at 555 nm) Lumen per Square Foot per Steradian to Millinits Candela per Square Meter to Blondels Lumen per Square Meter per Steradian to Millilamberts Lumen per Square Foot per Steradian to Candela per Square Meter Skot to Candela per Square Foot Candela per Square Meter to Lumens per Square Centimeter per Steradian Millilambert to Lumens per Square Centimeter per Steradian Blondel to Foot-Lamberts Millilambert to Lamberts Stilb to Lumens per Square Foot per Steradian Lumen per Square Centimeter per Steradian to Brils Candela per Square Centimeter to Millinits Millilambert to Candela per Square Centimeter Blondel to Stilbs Apostilb to Candela per Square Foot Stilb to Watts per Square Centimeter per Steradian (at 555 nm) Candela per Square Meter to Candela per Square Inch Millinit to Brils Candela per Square Foot to Apostilbs Lumen per Square Foot per Steradian to Candela per Square Centimeter Watt per Square Centimeter per Steradian (at 555 nm) to Lamberts Candela per Square Foot to Skots Bril to Lumens per Square Foot per Steradian Stilb to Apostilbs Nit to Candela per Square Foot Millilambert to Foot-Lamberts Skot to Nits Stilb to Millinits Blondel to Brils Nit to Candela per Square Inch Candela per Square Inch to Nits Blondel to Millinits Candela per Square Meter to Lamberts Skot to Kilocandela per Square Meter Nit to Watts per Square Centimeter per Steradian (at 555 nm) Stilb to Blondels Foot-Lambert to Lumens per Square Meter per Steradian Kilocandela per Square Meter to Candela per Square Foot Candela per Square Centimeter to Lumens per Square Centimeter per Steradian Foot-Lambert to Candela per Square Centimeter Millilambert to Watts per Square Centimeter per Steradian (at 555 nm) Lumen per Square Centimeter per Steradian to Millinits Lumen per Square Foot per Steradian to Stilbs Millinit to Lumens per Square Foot per Steradian Blondel to Candela per Square Inch Apostilb to Candela per Square Centimeter Bril to Candela per Square Meter Stilb to Candela per Square Meter Foot-Lambert to Blondels Kilocandela per Square Meter to Candela per Square Inch Millilambert to Candela per Square Inch Candela per Square Centimeter to Blondels Nit to Lumens per Square Meter per Steradian Kilocandela per Square Meter to Candela per Square Meter Watt per Square Centimeter per Steradian (at 555 nm) to Skots Blondel to Watts per Square Centimeter per Steradian (at 555 nm) Candela per Square Foot to Stilbs Blondel to Kilocandela per Square Meter Foot-Lambert to Millilamberts Candela per Square Meter to Millinits Candela per Square Inch to Apostilbs Lambert to Brils Blondel to Lumens per Square Meter per Steradian Candela per Square Centimeter to Brils Lumen per Square Foot per Steradian to Lumens per Square Meter per Steradian Lumen per Square Foot per Steradian to Lamberts Candela per Square Foot to Kilocandela per Square Meter Candela per Square Meter to Lumens per Square Foot per Steradian Lumen per Square Centimeter per Steradian to Nits Apostilb to Lamberts Foot-Lambert to Brils Lumen per Square Meter per Steradian to Stilbs Bril to Kilocandela per Square Meter Lumen per Square Centimeter per Steradian to Candela per Square Centimeter Candela per Square Foot to Candela per Square Meter Candela per Square Centimeter to Apostilbs Stilb to Nits Kilocandela per Square Meter to Nits Stilb to Kilocandela per Square Meter Lambert to Millilamberts Millinit to Candela per Square Inch Bril to Nits Millilambert to Skots Nit to Brils Skot to Candela per Square Meter Candela per Square Inch to Lumens per Square Foot per Steradian Millinit to Apostilbs Apostilb to Skots Watt per Square Centimeter per Steradian (at 555 nm) to Brils Apostilb to Kilocandela per Square Meter Candela per Square Foot to Blondels Apostilb to Millilamberts Skot to Millinits Candela per Square Inch to Watts per Square Centimeter per Steradian (at 555 nm) Candela per Square Inch to Millilamberts Lumen per Square Meter per Steradian to Kilocandela per Square Meter Lumen per Square Centimeter per Steradian to Lamberts Nit to Lumens per Square Foot per Steradian Blondel to Skots Nit to Millinits Candela per Square Meter to Lumens per Square Meter per Steradian Lumen per Square Centimeter per Steradian to Skots Kilocandela per Square Meter to Lumens per Square Centimeter per Steradian Stilb to Foot-Lamberts Candela per Square Inch to Candela per Square Meter Stilb to Candela per Square Foot Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Foot Candela per Square Meter to Candela per Square Foot Foot-Lambert to Candela per Square Foot Lumen per Square Centimeter per Steradian to Candela per Square Foot Foot-Lambert to Kilocandela per Square Meter Lambert to Watts per Square Centimeter per Steradian (at 555 nm) Stilb to Candela per Square Centimeter Lumen per Square Foot per Steradian to Apostilbs Watt per Square Centimeter per Steradian (at 555 nm) to Blondels Nit to Lumens per Square Centimeter per Steradian Skot to Candela per Square Inch Kilocandela per Square Meter to Watts per Square Centimeter per Steradian (at 555 nm) Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Centimeter Millilambert to Apostilbs Kilocandela per Square Meter to Blondels Lumen per Square Foot per Steradian to Skots Nit to Skots Blondel to Lamberts Millilambert to Brils Candela per Square Meter to Candela per Square Centimeter Lumen per Square Centimeter per Steradian to Candela per Square Inch Watt per Square Centimeter per Steradian (at 555 nm) to Millinits Watt per Square Centimeter per Steradian (at 555 nm) to Nits Bril to Lumens per Square Meter per Steradian Foot-Lambert to Nits Candela per Square Centimeter to Nits Candela per Square Foot to Lumens per Square Meter per Steradian Lumen per Square Foot per Steradian to Blondels Lambert to Candela per Square Inch Millilambert to Candela per Square Foot Candela per Square Centimeter to Lumens per Square Meter per Steradian Apostilb to Stilbs Millinit to Nits Kilocandela per Square Meter to Foot-Lamberts Lumen per Square Centimeter per Steradian to Candela per Square Meter Candela per Square Meter to Skots Candela per Square Centimeter to Lumens per Square Foot per Steradian Stilb to Brils Lambert to Foot-Lamberts Foot-Lambert to Lumens per Square Centimeter per Steradian Millinit to Skots Lumen per Square Meter per Steradian to Candela per Square Meter Candela per Square Foot to Millinits Blondel to Lumens per Square Foot per Steradian Candela per Square Foot to Lumens per Square Foot per Steradian Candela per Square Inch to Foot-Lamberts Lumen per Square Centimeter per Steradian to Foot-Lamberts Skot to Foot-Lamberts Lambert to Lumens per Square Foot per Steradian Bril to Watts per Square Centimeter per Steradian (at 555 nm) Candela per Square Centimeter to Lamberts Kilocandela per Square Meter to Candela per Square Centimeter Bril to Millilamberts Lumen per Square Centimeter per Steradian to Lumens per Square Meter per Steradian Candela per Square Centimeter to Stilbs Candela per Square Inch to Stilbs Kilocandela per Square Meter to Skots Watt per Square Centimeter per Steradian (at 555 nm) to Kilocandela per Square Meter Candela per Square Foot to Lumens per Square Centimeter per Steradian Watt per Square Centimeter per Steradian (at 555 nm) to Lumens per Square Centimeter per Steradian Foot-Lambert to Candela per Square Inch Millilambert to Millinits Apostilb to Lumens per Square Foot per Steradian Candela per Square Foot to Nits Watt per Square Centimeter per Steradian (at 555 nm) to Apostilbs Foot-Lambert to Skots Candela per Square Centimeter to Foot-Lamberts Candela per Square Foot to Foot-Lamberts Skot to Lumens per Square Foot per Steradian Candela per Square Foot to Watts per Square Centimeter per Steradian (at 555 nm) Lumen per Square Foot per Steradian to Nits Lumen per Square Meter per Steradian to Brils Lumen per Square Meter per Steradian to Lumens per Square Foot per Steradian Kilocandela per Square Meter to Apostilbs Candela per Square Foot to Candela per Square Centimeter Lumen per Square Meter per Steradian to Watts per Square Centimeter per Steradian (at 555 nm) Foot-Lambert to Lamberts Millinit to Lumens per Square Meter per Steradian Millilambert to Lumens per Square Foot per Steradian Watt per Square Centimeter per Steradian (at 555 nm) to Foot-Lamberts Lumen per Square Foot per Steradian to Candela per Square Inch Apostilb to Foot-Lamberts Stilb to Lumens per Square Centimeter per Steradian Blondel to Candela per Square Meter Nit to Millilamberts Lambert to Blondels Lumen per Square Centimeter per Steradian to Apostilbs Nit to Lamberts Lambert to Nits Lumen per Square Foot per Steradian to Candela per Square Foot Bril to Lamberts Bril to Foot-Lamberts Blondel to Nits Candela per Square Centimeter to Watts per Square Centimeter per Steradian (at 555 nm) Bril to Apostilbs Lumen per Square Centimeter per Steradian to Kilocandela per Square Meter Lumen per Square Meter per Steradian to Apostilbs Skot to Stilbs Lumen per Square Foot per Steradian to Brils Apostilb to Candela per Square Inch Apostilb to Brils Watt per Square Centimeter per Steradian (at 555 nm) to Lumens per Square Meter per Steradian Millinit to Millilamberts Lumen per Square Meter per Steradian to Foot-Lamberts Kilocandela per Square Meter to Brils Millilambert to Lumens per Square Meter per Steradian Lumen per Square Meter per Steradian to Candela per Square Foot Candela per Square Foot to Brils Candela per Square Meter to Nits Apostilb to Lumens per Square Meter per Steradian Lumen per Square Centimeter per Steradian to Blondels Lambert to Millinits Nit to Candela per Square Centimeter Candela per Square Meter to Foot-Lamberts Blondel to Apostilbs Kilocandela per Square Meter to Millinits Candela per Square Foot to Candela per Square Inch Bril to Blondels Candela per Square Centimeter to Candela per Square Meter Millinit to Lumens per Square Centimeter per Steradian Blondel to Lumens per Square Centimeter per Steradian Skot to Millilamberts Lumen per Square Foot per Steradian to Lumens per Square Centimeter per Steradian Stilb to Millilamberts Candela per Square Meter to Watts per Square Centimeter per Steradian (at 555 nm) Apostilb to Candela per Square Meter Millilambert to Stilbs Watt per Square Centimeter per Steradian (at 555 nm) to Millilamberts Lumen per Square Meter per Steradian to Skots Watt per Square Centimeter per Steradian (at 555 nm) to Candela per Square Inch Millilambert to Kilocandela per Square Meter Stilb to Lamberts Foot-Lambert to Apostilbs Lambert to Lumens per Square Centimeter per Steradian Millinit to Watts per Square Centimeter per Steradian (at 555 nm) Millilambert to Blondels Bril to Lumens per Square Centimeter per Steradian Apostilb to Watts per Square Centimeter per Steradian (at 555 nm) Lambert to Skots Bril to Candela per Square Foot Apostilb to Blondels Bril to Candela per Square Centimeter Millinit to Candela per Square Centimeter Watt per Square Centimeter per Steradian (at 555 nm) to Lumens per Square Foot per Steradian Candela per Square Meter to Apostilbs Candela per Square Inch to Blondels Bril to Candela per Square Inch Nit to Apostilbs Stilb to Lumens per Square Meter per Steradian Lumen per Square Centimeter per Steradian to Lumens per Square Foot per Steradian Apostilb to Nits Lumen per Square Meter per Steradian to Blondels Millinit to Lamberts Lumen per Square Centimeter per Steradian to Millilamberts Candela per Square Inch to Brils Millinit to Candela per Square Meter Candela per Square Inch to Skots Millinit to Candela per Square Foot Lambert to Candela per Square Centimeter Lambert to Candela per Square Foot Foot-Lambert to Candela per Square Meter Kilocandela per Square Meter to Lumens per Square Foot per Steradian Foot-Lambert to Lumens per Square Foot per Steradian Lambert to Lumens per Square Meter per Steradian Skot to Brils Candela per Square Centimeter to Skots Bril to Stilbs Candela per Square Foot to Millilamberts Millilambert to Candela per Square Meter Candela per Square Foot to Lamberts Kilocandela per Square Meter to Stilbs Skot to Lumens per Square Centimeter per Steradian Candela per Square Inch to Lamberts Millilambert to Nits Lumen per Square Meter per Steradian to Lumens per Square Centimeter per Steradian Kilocandela per Square Meter to Lumens per Square Meter per Steradian Candela per Square Meter to Stilbs Nit to Candela per Square Meter Lumen per Square Meter per Steradian to Nits Stilb to Skots Candela per Square Inch to Millinits Lambert to Apostilbs Candela per Square Inch to Kilocandela per Square Meter Skot to Apostilbs Nit to Kilocandela per Square Meter Bril to Skots Candela per Square Meter to Millilamberts Watt per Square Centimeter per Steradian (at 555 nm) to Stilbs Nit to Stilbs Kilocandela per Square Meter to Millilamberts Candela per Square Centimeter to Candela per Square Inch Apostilb to Lumens per Square Centimeter per Steradian Candela per Square Centimeter to Kilocandela per Square Meter Candela per Square Inch to Candela per Square Foot Foot-Lambert to Watts per Square Centimeter per Steradian (at 555 nm) Bril to Millinits Skot to Lumens per Square Meter per Steradian Stilb to Candela per Square Inch Skot to Lamberts Skot to Blondels Millinit to Blondels Candela per Square Inch to Lumens per Square Centimeter per Steradian Candela per Square Inch to Lumens per Square Meter per Steradian Millinit to Foot-Lamberts Lumen per Square Foot per Steradian to Kilocandela per Square Meter Candela per Square Centimeter to Candela per Square Foot Lambert to Kilocandela per Square Meter Candela per Square Meter to Kilocandela per Square Meter Foot-Lambert to Stilbs Lumen per Square Meter per Steradian to Lamberts Candela per Square Inch to Candela per Square Centimeter Lumen per Square Meter per Steradian to Candela per Square Inch Lumen per Square Meter per Steradian to Millinits Lambert to Candela per Square Meter

See also