Convert illuminance between lux, foot-candles, phot, milliphot and nox, or switch to luminance and convert nits (cd/m²), foot-lamberts, stilb, lamberts and apostilbs. Add a surface reflectance to estimate how bright a matte surface looks under a given light level.
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Links lux and nits for a matte (diffuse) surface: white paper ≈ 80%, grey card 18%. Leave blank to skip.
Enter your values to see the result.
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How to use the Light Illuminance Converter
Choose the quantity: illuminance (light falling on a surface) or luminance (brightness of a surface or screen).
Enter the value and pick the From and To units.
Read the result and the full table of every unit below it.
Optionally set a reflectance to link lux and nits for a matte surface.
Copy the results or download the unit table as CSV.
Illuminance vs luminance
Illuminance is how much light falls on a surface, measured in lux (lumens per square meter) or foot-candles (lumens per square foot). It is what a light meter held flat on a desk reads, and what lighting guidelines specify for offices, classrooms and grow rooms.
Luminance is how bright a surface looks: the light it emits or reflects toward your eye, measured in candela per square meter (nits) or foot-lamberts. Screen and projector brightness are quoted as luminance.
The two are linked by the surface. For an ideal matte (Lambertian) surface with reflectance ρ, L (nits) = E (lux) × ρ ÷ π. White paper (about 80% reflectance) under 500 lux looks roughly 127 nits bright. Shiny or colored surfaces do not follow this exactly, which is why the tool labels it an estimate.
Ranges are typical values for orientation, not specifications; real devices and conditions vary.
Frequently asked questions
How many lux is 1 foot-candle?
1 foot-candle equals 10.7639 lux, because a foot-candle is one lumen per square foot and a square foot is 0.09290304 m². So 1 lux = 0.0929 fc.
What is a phot and a nox?
Both are old units of illuminance. 1 phot is one lumen per square centimeter, or 10,000 lux. 1 nox is one thousandth of a lux, used for very dim night-time light.
What is the difference between lux and nits?
Lux measures light arriving at a surface (illuminance); nits (cd/m²) measure how bright a surface or screen appears (luminance). They are different quantities, so you can only relate them through a surface's reflectance.
How do I convert lux to nits?
For a matte surface, nits = lux × reflectance ÷ π. A white page at 80% reflectance under 500 lux is about 500 × 0.8 ÷ 3.1416 ≈ 127 nits. The tool does this when you enter a reflectance.
How many nits is 1 foot-lambert?
1 foot-lambert = 3.4263 nits (cd/m²). Cinema screens are traditionally calibrated to 14 fL, which is about 48 nits.
How much light does an office need?
Many lighting guidelines recommend roughly 300 to 500 lux (about 28 to 46 foot-candles) on desks for general office work, with more for detailed tasks.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.