Illuminance Converter

Convert between lux, foot-candles, and phot — the measure of how much light falls on a surface, for lighting, photography, and horticulture.

Illuminance

lux, foot-candle, phot

From

Result

0.092903

1 lx = 0.09290304 fc

Popular conversions

What Is an Illuminance Converter?

An illuminance converter translates how much light lands on a surface between units — lux to foot-candles, phot to lux. Illuminance is luminous flux per unit area, the SI unit being the lux (lx): one lumen per square metre. The US lighting industry uses the foot-candle (one lumen per square foot), so converting between lux and foot-candles is the everyday task in lighting design.

This converter routes through the lux. One foot-candle is about 10.764 lux (the same ratio as square feet to square metres), and the older CGS unit phot equals 10,000 lux. From the ~500 lux of an office to the ~100,000 lux of direct sun, illuminance spans a wide range that these units cover.

This is one category of the full Unit Converter — pair it with our percentage calculator or scientific calculator for related everyday maths.

How Illuminance Conversion Works

Everything routes through the lux

Each unit has a fixed lux factor. The converter normalises to lux, then projects to foot-candles and phot.

Illuminance is lumens per area

1 lx = 1 lumen/m². It measures light arriving on a surface, distinct from how bright the source itself looks.

Lux ↔ foot-candle uses 10.764

A foot-candle is one lumen per square foot, so 1 fc = 10.764 lx — the same factor as ft² to m².

Distance dims by the inverse square

Illuminance falls with the square of distance from a point source. Doubling the distance quarters the lux on the surface.

Core Illuminance Conversion Factors

Multiply to reach lux; divide to come back.

Foot-candle → lux

× 10.7639

One foot-candle is 10.764 lux — one lumen per square foot versus per square metre.

Phot → lux

× 10000

One phot (CGS) is 10,000 lux — one lumen per square centimetre.

Lux definition

lx = lm / m²

One lux is one lumen of luminous flux spread over one square metre.

How to Use the Illuminance Converter

1
Enter the illuminance value
Type the light level you want to convert — a lighting spec, a meter reading, a horticulture target.
2
Choose the 'from' unit
Pick lux, foot-candles, or phot as your starting unit.
3
Choose the 'to' unit
Select the target unit, or swap the two to reverse direction.
4
Read every unit at once
The all-units table shows the illuminance in lux, foot-candles, and phot together.

Key Illuminance Concepts

Lux

The SI unit of illuminance: one lumen per square metre. An office is ~500 lx; overcast daylight ~1,000 lx; direct sun ~100,000 lx.

Foot-candle

One lumen per square foot, equal to 10.764 lux. The traditional US unit for lighting design and codes.

Illuminance vs luminance

Illuminance is light falling on a surface (lux); luminance is light emitted or reflected toward the eye (cd/m²). Different quantities.

Inverse-square falloff

From a point source, illuminance drops as 1/distance². This is why lighting layouts space fixtures to keep levels even.

Real-World Illuminance Conversions

🏢

Office lighting

Offices target ~500 lux (46 fc). Lighting codes specify lux in metric regions and foot-candles in the US.

☀️

Daylight

Direct sunlight is about 100,000 lux (9,290 fc); overcast sky ~1,000 lux. Photography and solar work use these benchmarks.

🌱

Plant growth

Seedlings want 5,000–10,000 lux; fruiting plants more. Horticulture lighting is specified in lux (and PPFD).

📷

Photography

Light meters read lux or foot-candles to set exposure. A studio might run several thousand lux at the subject.

🛣️

Street lighting

Roadways are lit to ~10–30 lux. Municipal lighting standards specify minimum lux at the pavement.

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Task areas

Surgical and detailed-work areas need 1,000+ lux. Codes set minimum illuminance for safe, accurate work.

Best Practices for Illuminance Conversion

✓Use 10.764 for lux ↔ foot-candle. The factor is the same as square feet to square metres. A rough '1 fc ≈ 10 lux' is close but ~7% low for precise lighting work.
✓Keep illuminance and luminance separate. Lux measures light on a surface; cd/m² measures light from a surface. They answer different questions and aren't interchangeable.
✓Account for inverse-square falloff. Illuminance depends on distance from the source. A converted lux figure applies at the measured distance, not everywhere.
✓Match the unit to the code. US lighting codes use foot-candles; metric ones use lux. Convert to the unit your standard or client expects.
✓Mind spectrum for plants. Lux is weighted to human vision, not plant response. Horticulture also uses PPFD (µmol/m²/s); lux alone can mislead for growth.

Common Illuminance Conversion Mistakes

Using 1 fc = 10 lux

The exact factor is 10.764. The rounded 10 is about 7% low — fine for a rough check, wrong for compliant lighting design.

Confusing lux with lumens

Lumens measure total light output; lux measures light per area on a surface. A bright bulb spread over a large area gives low lux.

Mixing illuminance and luminance

Lux (on a surface) and cd/m² (from a surface) are different. Treating one as the other misjudges either lighting level or screen brightness.

Ignoring distance

Illuminance falls with distance squared. A lux reading taken close to a lamp doesn't hold at the far side of the room.

Why Illuminance Conversion Matters

Illuminance determines whether a workspace is safe and comfortable, whether a photo is correctly exposed, and whether plants get enough light — and lighting codes split between lux (metric) and foot-candles (US). A sloppy conversion can leave an office under-lit against code or a grow operation short of its light target.

Because illuminance also falls off with the square of distance and is easily confused with lumens or luminance, getting both the unit and the concept right matters. A converter that routes through the lux with the exact 10.764 factor lets lighting designers, photographers, and growers specify and verify light levels across both unit systems.

Built for lighting designers, photographers, horticulturists, and facilities staff converting between lux and foot-candles.

Linear unit factors follow the BIPM SI brochure, the NIST Guide to the SI, and ISO 80000. Currency rates load live from open.er-api.com; crypto prices from CoinGecko. See our methodology and editorial policy. Educational only — not certified for regulated trading, settlement, medical, or aerospace use.

Illuminance Converter FAQs

Divide lux by 10.764 to get foot-candles, or multiply foot-candles by 10.764 to get lux. So a 500-lux office is about 46 foot-candles. The factor matches the square-foot-to-square-metre ratio, because a foot-candle is one lumen per square foot and a lux is one lumen per square metre.

The lux (lx) is the SI unit of illuminance, equal to one lumen of luminous flux spread over one square metre. It measures how much light falls on a surface — an office is about 500 lux, overcast daylight around 1,000 lux, and direct sunlight roughly 100,000 lux.

Lumens measure the total amount of visible light a source emits; lux measures how much of that light lands on each square metre of a surface. The same number of lumens gives high lux on a small area and low lux when spread over a large one, so lux depends on both the source and the distance.

Illuminance (lux) is the light falling onto a surface; luminance (candela per square metre) is the light emitted or reflected from a surface toward your eye. Illuminance describes how well-lit a desk is; luminance describes how bright a screen or lamp appears. They're related but distinct quantities.

Because light from a point source spreads out over an increasing area as it travels, illuminance follows an inverse-square law: doubling the distance reduces the lux to one-quarter. This is why lighting designers space and aim fixtures carefully to keep illuminance even across a room or roadway.

It uses the exact factor (1 foot-candle = 10.7639 lux, derived from the square-foot-to-square-metre ratio, and 1 phot = 10,000 lux) and routes every conversion through the lux at full precision, so the result is exact to your input precision.