Luminance Converter
Enter a luminance in any common unit and see it in all the others instantly: candela per square metre (cd/m², the nit), stilb (sb, cd/cm²), apostilb (asb, also called the blondel), lambert (L), foot-lambert (fL) and skot (sk). The value is converted to cd/m² internally using the exact definitions, including the 1/π factors that the lambert family carries, so conversions are precise. Useful for display and TV brightness specs (nits), cinema projection standards (foot-lambert), photometry lab work and aviation or automotive instrument legibility. Everything is computed locally in your browser.
cd/m² (nit)
100
sb (stilb)
0.01
asb (blondel)
314.15927
L (lambert)
0.03141593
fL (foot-lambert)
29.186351
sk (skot)
314,159.27
How to use
- Type a luminance value.
- Pick the unit you entered it in.
- Read the value in every other unit and copy whichever you need.
Frequently asked questions
- Are nits and cd/m² the same thing?
- Yes, exactly the same — the nit is just a shorter name for the candela per square metre. A monitor rated 400 nits is 400 cd/m². Because they are identical they share one row here instead of appearing twice.
- How do I convert cd/m² to foot-lamberts?
- Divide by 3.4262591, since one foot-lambert is (1/π) candela per square foot. The SMPTE reference white for cinema projection is 14 fL, which works out to about 48 cd/m² — the number you will see quoted for calibrated theatre screens.
- What is the difference between luminance and illuminance?
- Luminance is how bright a surface looks to the eye, in cd/m² — it describes light leaving a surface. Illuminance is how much light falls onto a surface, in lux. A screen has a luminance; the light hitting your desk is an illuminance. Use the Illuminance Converter for lux and foot-candles.
- Why do lamberts involve π?
- The lambert family was defined for a perfectly diffusing (Lambertian) surface, where light spreads over a hemisphere. That geometry introduces a factor of π, so one lambert is 10,000/π cd/m² and one apostilb is 1/π cd/m². The skot is a milli-apostilb, used for very dim, dark-adapted viewing.
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