Lux Calculator — Convert Lux to Foot-Candles and Find Target Levels

This converter pairs with the main recessed lighting calculator for anyone who needs lux instead of foot-candles. Lux is the illuminance unit most of the world runs on — Europe, Asia, Australia and nearly every country except the United States writes its lighting codes in lux, not foot-candles. If you're specifying fixtures from a European catalog, following an EN or ISO standard, or you just prefer working in metric, this page converts your numbers and tells you what to target.

What Lux Actually Measures

Lux measures illuminance: the amount of visible light landing on a given area, expressed as lumens per square metre. One lux is one lumen spread evenly over one square metre. It doesn't matter what produces the light — sunlight, an LED downlight, a candle — lux only counts how much of it lands on the surface you're standing on, reading at, or chopping vegetables over.

Distance changes the lux reading even when the fixture doesn't change. A 1,000-lumen LED downlight mounted 2 m above the floor delivers roughly 200 lx (19 fc) directly underneath it. Move the same fixture up to a 3 m ceiling and it delivers about 90 lx (8 fc) at that same spot on the floor, because the light spreads over a wider circle and illuminance falls with the square of the distance, not in a straight line. Mounting height matters as much as fixture output when you plan a room.

Lux vs. Foot-Candles: Converting Both Ways

Lux and foot-candles measure the same quantity, illuminance, in two different unit systems. One foot-candle is one lumen per square foot; one lux is one lumen per square metre. A square metre holds more square feet than a square foot holds square metres, and that ratio is where the fixed conversion factor of 10.764 comes from.

To go from lux to foot-candles, divide by 10.764, exactly what the converter above does. To go the other way, multiply by 10.764. If you're starting from an imperial fc reading and want the lux side of the math, run it through the dedicated foot-candle converter instead. It applies the same factor in reverse.

Lux vs. Lumens: Output vs. Illuminance

Lumens and lux get confused constantly, but they describe different things. Lumens measure total light output — how much light a bulb or fixture produces, full stop, regardless of where that light ends up. Lux measures illuminance — how much of that output actually lands on one specific surface. A fixture's lumen rating is fixed the moment it's manufactured; the lux it delivers to your countertop depends on mounting height, beam angle, room reflectance, and how far you're standing from the source.

That's why two identical 1,000-lumen fixtures can produce very different lux readings in two different rooms. A narrow-beam fixture mounted low over a desk concentrates its lumens into a small, bright patch of high lux. The same fixture mounted high in a wide, dark-painted room spreads its lumens thin and reads much lower on a lux meter, even though the lumen figure printed on the box hasn't changed. Use lumens to compare fixtures on the shelf; use lux, checked with the calculator above, to confirm that output actually meets the target once it's installed in your room.

Lux Target Levels for Residential and Commercial Spaces

Target lux depends on what happens in the room, not on the room's size. A hallway only needs enough light to walk safely; a retail display needs enough to make merchandise pop. The tables below split common residential rooms from the commercial and retail spaces that come up most often, with the foot-candle equivalent alongside so you can cross-check against a U.S. spec sheet.

Residential Lux Targets

Commercial and Retail Lux Targets

A Worked Example: Lighting a Home Office to 500 Lux

Say you're lighting a 12 ft × 10 ft home office (about 3.66 m × 3.05 m, or 11.2 m² of floor area) and you want the standard desk-level target of 500 lx (46 fc).

First, find the total lumens needed: multiply area by target lux. 11.2 m² × 500 lx = 5,600 lm. That's the combined output every fixture in the room needs to produce, measured at desk height.

Next, pick a fixture. A common 6-inch LED downlight puts out about 900 lumens. Divide the total lumens needed by the per-fixture output: 5,600 lm ÷ 900 lm = 6.2. You can't install a fraction of a downlight, so round up to 7 fixtures rather than down to 6. Rounding down would leave the room just under target.

Check the result: 7 fixtures × 900 lm = 6,300 total lumens. Divide by the room area: 6,300 lm ÷ 11.2 m² = 562 lx (52 fc). That's comfortably over the 500 lx target, which gives you margin for light lost to a lampshade, a dimmer set below full, or a dark accent wall. Plug the same area and target lux into the lumens calculator at the top of this page to run the same math for any room, then divide by your chosen fixture's rated lumens to get a fixture count.

How Lux Is Measured: Meters and Phone Apps

A calibrated lux meter is the accurate way to check illuminance. Hold the sensor flat at the work plane — desk height for an office, counter height for a kitchen, floor level for a hallway — facing straight up toward the ceiling, not toward the fixture. Take several readings across the surface instead of one directly under a single fixture, and average them. Task surfaces need even lux across their length, not just a bright spot in the middle.

Smartphone lux apps use the phone's camera or ambient light sensor and work fine for a rough check, but they typically read 10–20% low against a proper meter, and an uncalibrated or low-quality app can be off by much more. If you're checking against a hard requirement — an egress corridor, a workplace safety minimum — use a real meter, not a phone. If you're just planning a room from scratch, pair a rough phone reading with the grid layout planner to see how many fixtures at what spacing will actually hit your target, instead of guessing and re-measuring after the fixtures are already installed.

Reviewed by the Recessed Light Calculator editorial team using IESNA lumen-method formulas · Last updated July 2026

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