Luminance / asb → fL
Convert Apostilbs to Foot-lamberts
Convert visible-light luminance in candela per projected area. Convert Apostilbs (asb) to Foot-lamberts (fL). Find the formula, worked examples, unit definitions, and practical guidance below.
Reverse: Foot-lamberts to Apostilbs →
How to convert apostilbs to foot-lamberts
Luminance describes directional brightness weighted for human vision. It differs from illuminance on a surface and cannot be converted to lux without geometry.
Use x for the value in asb, b for the intermediate value in cd/m², and y for the result in fL.
fL = asb × 0.3183098861837907 ÷ 3.4262590996353905
Worked examples
10 asb ≈ 0.9290304 fL
Step 1: (10 × 0.318309886184) ≈ 3.18309886184 cd/m².
Step 2: 3.18309886184 ÷ 3.42625909964 ≈ 0.9290304 fL.20 asb ≈ 1.8580608 fL
Step 1: (20 × 0.318309886184) ≈ 6.36619772368 cd/m².
Step 2: 6.36619772368 ÷ 3.42625909964 ≈ 1.8580608 fL.
Results are rounded to 12 significant digits. Converting units does not increase the precision of the original measurement. Very large or small values outside JavaScript’s finite numeric range are rejected.
About Apostilbs
Apostilbs (asb) measures luminance under the conventions above. The base value in cd/m² is (x × 0.318309886184), where x is the numerical value in asb. Factors shown here are rounded for display; calculations use the stored factor.
About Foot-lamberts
Foot-lamberts (fL) measures luminance under the conventions above. The base value in cd/m² is (x × 3.42625909964), where x is the numerical value in fL. Factors shown here are rounded for display; calculations use the stored factor.
Definitions and sources
Carry the same physical assumptions into subsequent physics calculations.
Apostilbs to foot-lamberts reference table
| Apostilbs (asb) | Foot-lamberts (fL) |
|---|---|
| 1 | 0.09290304 |
| 5 | 0.4645152 |
| 10 | 0.9290304 |
| 25 | 2.322576 |
| 50 | 4.645152 |
| 100 | 9.290304 |
| 1000 | 92.90304 |
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