Before using this illuminance result
- Keep the measurement plane and location with the reading.
- Distinguish surface illuminance from lamp output and display luminance.
- Retain the meter’s calibration and any stated measurement uncertainty.
Keep the original illuminance value, its unit and the relevant conditions in the record. A copied answer of 46.45152 fc is interpretable only when those details remain available. State which of the measurement checks above you verified before using the value in another calculation.
A room needs more than one light-meter reading
A lighting survey records 500 lux at a desk and a comparison document uses foot-candles. Converting the number aligns the illuminance unit. It does not make a single desk reading describe the whole room or establish whether the survey used the correct measurement plane.
A surface reading of 500 lx is about 46.4515 foot-candles. This describes light arriving at that measuring location and plane. It does not describe the lamp's total lumen output or the directional luminance of a display. Similar-looking lighting terms require different physical models.
For an illustrative set of readings of 300, 500 and 700 lx, the simple arithmetic average is 500 lx. The minimum is still 300 lx. A real lighting assessment may prescribe a grid, weighting and measurement conditions; three convenient points are not automatically an acceptable survey. Preserve the applicable method rather than turning a sample average into a compliance claim.
Surface orientation, shadows, daylight and instrument response can affect readings. Compare measurements taken under like conditions and retain the plane height or location when it matters. A useful room record separates point values, a defined average and the minimum. The conversion can translate each statistic into foot-candles without changing how the statistic was obtained.
A 500 lx point measurement is about 46.4515 foot-candles.
Keep point readings and averages separate
For a lighting report, convert the readings into one unit and preserve their locations and measurement plane. Keep average and minimum values as distinct summaries.
The following inputs stay in lux and the results use foot-candles. They illustrate different magnitudes for this measurement. Retain the specific conditions described above when replacing an example with your own value.
This illuminance unit pair has a constant factor ratio. Changing the input changes the output by the same proportion. If a copied figure differs by an unexpected factor, review the full unit symbol before changing the source measurement. Measure or model an appropriate set of locations for that task.
Record the location and plane of each reading, then calculate any average or minimum using the survey method required by the task.
Illuminance units, side by side
The values below all describe 500 lx. They provide a comparison of unit sizes for illuminance; they are not separate measurements. Read the complete symbol and convention before copying a number.
| Unit | Symbol | Equivalent |
|---|---|---|
| Lux | lx | 500 lx |
| Kilolux | klx | 0.5 klx |
| Foot-candles | fc | 46.45152 fc |
| Phots | phot | 0.05 phot |
Keep the original lux record alongside the converted foot-candles display. The unit list uses up to twelve significant digits for arithmetic readability, while the measurement precision still comes from its source.
Light arriving at a measurement plane
Illuminance describes visible light arriving at a surface, reported in lux or related units. Use this converter for supplied lighting measurements in lux, kilolux, foot-candles or phots. A lux reading is not a lumen output rating and is not the same quantity as display luminance.
One lux is one lumen per square metre. A foot-candle is one lumen per square foot, so area conversion connects the units. A phot is 10,000 lux. A measurement depends on the surface location, orientation and instrument response; it cannot by itself describe the distribution of light throughout a room.
Illuminance is light arriving at a surface per area. The relation between lux and foot-candles follows the square-metre versus square-foot denominator. Lamp lumens describe a different quantity, while display luminance describes another. Position, surface orientation and meter response affect measurements; a unit equivalent cannot supply an average or minimum across unmeasured points.
Record the location and plane of each reading, then calculate any average or minimum using the survey method required by the task.
500 lx in foot-candles
500 lx = 46.45152 fc
Output = input × source factor ÷ destination factor500 × 1 ÷ 10.7639104167 = 46.45152 fc. The two factors express the source and destination relative to the same internal reference unit. Their ratio is the multiplier.
Both unit factors refer to the same internal reference for illuminance. Multiplying by the source factor and dividing by the destination factor changes the numerical scale while retaining the quantity. The source definition still matters: An area or a light-distribution model is needed.
Reversing the unrounded 46.45152 fc result returns 500 lx. Use this as a direction check. A consistent reverse calculation cannot resolve converting lumens directly into lux or improve the original observation.
Questions about illuminance
Is a foot-candle the same as a candlepower rating?
No. A foot-candle is illuminance, while candlepower refers to luminous intensity. Similar historical names do not make the quantities interchangeable.
Can this determine whether a room meets a standard?
It translates a measurement. A compliance assessment also needs the applicable standard, measurement locations, averaging method and conditions.
What this illuminance comparison can tell you
Useful capabilities
Record the location and plane of each reading, then calculate any average or minimum using the survey method required by the task.
The listed units express the same supplied illuminance quantity. The 500 lx → 46.45152 fc example makes the selected convention visible before it is used in a longer calculation.
Important limits
Illuminance describes light arriving at a surface. Lumens and luminance describe other properties.
An area or a light-distribution model is needed. Measure or model an appropriate set of locations for that task.
Converting lumens directly into lux
An area or a light-distribution model is needed.
Using one point reading as the whole room average
Measure or model an appropriate set of locations for that task.
One lux reading describes one location and plane under particular conditions. A room survey may require a prescribed grid and averaging method. Keep average, minimum and point values distinct rather than using the converted average to imply uniform illumination. Daylight, shadows and instrument response can affect the observations. Unit conversion alone cannot establish whether an assessment follows a lighting standard.
As a controlled uncertainty example, suppose the original 500 lx record had a stated ±1% input interval. Its endpoints would be 495 lx and 505 lx. Converting those endpoints gives an output interval from 45.9870048 fc to 46.9160352 fc. The interval scales with the same fixed unit ratio as the central value. This chosen interval illustrates the arithmetic and is not an accuracy claim for your measurement.