Unit Converters
Illuminance Converter Calculator
Convert illuminance through lux, derive foot-candles and less common metric units, and show optional scaling, tolerance, repeated-value arithmetic, and comparison with a lux reference. The explanation distinguishes measured illuminance from lumens, luminance, and visual comfort.
Lux-
Foot-candles-
Phot-
Nox-
Scaled lux-
Batch total in lux-
Lower tolerance reference-
Upper tolerance reference-
Difference from entered reference-
Decision view
Illuminance task-reference band
Illuminance task-reference bandThe live lux value is placed on a logarithmic lighting-context band while foot-candle, phot, and nox equivalents stay explicit.
Exact scenario comparisonIlluminance value changes while all other entered assumptions remain constant.
| Illuminance value | Lux | Foot-candles | Phot | Nox | Scaled lux | Batch total in lux | Lower tolerance reference | Upper tolerance reference | Difference from entered reference |
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How to use Illuminance Converter Calculator
- Enter the measured or specified illuminance and select its source unit.
- Confirm the sensor plane, location, time, daylight contribution, and luminaire state before comparing readings.
- Use the converted value with a lighting standard that also addresses uniformity, glare, colour rendering, and task requirements.
Calculator guide
Understanding Illuminance Converter Calculator
Illuminance is luminous flux falling on a surface per unit area. This page converts the same task-plane illuminance among lux, foot-candles, phot, and nox while keeping lighting quality, glare, uniformity, and source output outside the unit conversion.
Detailed calculation process
Convert illuminance through lux
The default converts 500 lux, applies no scaling, uses a 2% tolerance, and compares the result with the entered lux reference.
General formula: E_lx = x × f_inE_fc = E_lx / 10.7639104E_phot = E_lx / 10,000E_nox = E_lx × 1,000E_s = E_lx × kE_total = E_s × nE_low = E_s × (1 - t/100)E_high = E_s × (1 + t/100)ΔE = E_s - E_ref The source factor converts the reading to lux. Foot-candles divide by the exact area-unit relationship, phot divides by ten thousand, and nox multiplies by one thousand. Scenario modifiers operate on the lux base after conversion.
What each symbol means
Worked substitution with the default inputs
The target-unit values all return to 500 lux, but lighting adequacy still depends on where and how the illuminance was measured.
Purpose-built visual
Illuminance task-reference band
A logarithmic reference band locates the live lux value among broad lighting contexts while keeping converted units visible.
Worked situations
Practical examples
- An office task-plane reading of 500 lux equals approximately 46.4515 foot-candles, 0.050 phot, and 500,000 nox.
- A 300 lux corridor criterion converts to approximately 27.8709 foot-candles.
- A 1,000 lux inspection target equals approximately 92.9030 foot-candles; it does not mean the source emits 1,000 lumens.
Better inputs
Useful tips
- Use illuminance measured on the working plane rather than a fixture's lumen rating.
- Keep lux and foot-candle readings tied to the same sensor position, height, and orientation.
- Take several readings across the space when uniformity matters; one converted point does not describe the whole area.
Before relying on the result
Limitations and common mistakes
- The conversion does not predict glare, uniformity, shadows, colour rendering, flicker, spectral response, or visual comfort.
- Lux is illuminance at a surface, not total lamp lumens or luminance observed from a surface.
- Measured results depend on sensor calibration, cosine response, placement, orientation, daylight, dirt, ageing, and operating conditions.
Reference
Key terms
- Illuminance
- Luminous flux received per unit area of a surface.
- Lux
- One lumen per square metre, the SI illuminance unit.
- Foot-candle
- One lumen per square foot, equal to 10.7639104 lux.
- Task plane
- The surface and orientation where illuminance is evaluated for a visual task.
Important note
Attach a location, plane height, orientation, time, and operating condition to every illuminance record. A converted number without measurement context cannot demonstrate compliance or lighting quality.
Frequently asked questions
How many lux are in one foot-candle?
One foot-candle equals exactly 10.7639104 lux based on the area definitions.
Can lux be converted to lumens?
Only with the illuminated area and distribution. For uniform illumination, lumens on the surface equal lux multiplied by square metres.
Why do readings change when the meter is tilted?
Illuminance depends on the angle at which light reaches the sensor, and real meters also have cosine-response limitations.
Does meeting an average lux target guarantee a good design?
No. Uniformity, glare, shadows, colour quality, controls, and the actual visual task also matter.