Lumens and lux get used interchangeably in lighting marketing, but they measure two different things: lumens measure how much light a source emits; lux measures how much of that light actually lands on a surface. You buy lumens — you live in lux. Confusing the two is the most common reason a room ends up dimmer (or harsher) than planned.
Lumens: Light Leaving the Source
A lumen (lm) is the unit of luminous flux — the total amount of visible light a source emits in all directions, weighted by how sensitive the human eye is to each wavelength. It's the number on the box: an LED strip might emit 1,500 lm per meter, a downlight 800 lm. Lumens say nothing about where that light goes or how concentrated it is when it arrives.
Lux: Light Arriving at a Surface
Lux (lx) is the unit of illuminance — luminous flux per unit area. One lux is one lumen spread over one square meter (1 lx = 1 lm/m²). Lux is what a light meter reads on your desk, your countertop, or a gallery wall, and it's what lighting standards actually specify. In North America you'll also meet the foot-candle: one lumen per square foot, equal to about 10.76 lux.
The same source produces very different lux depending on distance and geometry: 800 lm concentrated on a reading desk from half a meter gives high illuminance; the same 800 lm washed across a whole wall from a cove gives a soft, low-lux glow. Same lumens — completely different result.
Converting Lumens to Lux (and Back)
For light spread evenly over an area: lux = lumens ÷ area in square meters. Flip it to size a room: lumens needed = target lux × area. Real rooms aren't ideal — some light is absorbed by surfaces, some never reaches the work plane, indirect layouts (coves, uplights) lose more — so plan roughly 1.5–2× the ideal figure for direct lighting, more for fully indirect schemes.
Worked example: a 20 m² living room at a comfortable 150 lx needs about 3,000 lm actually delivered to the room's surfaces. With realistic losses, that means specifying roughly 4,500–6,000 installed lumens, split across layers — ambient, task, accent — rather than one blazing central fixture.
How Many Lux Do You Need? Room-by-Room Targets
Commonly recommended illuminance ranges for residential and commercial interiors:
| Space / task | Typical target |
|---|---|
| Hallways, corridors | 100–150 lx |
| Living rooms (ambient) | 100–300 lx |
| Bedrooms | 100–200 lx |
| Kitchen — general | ~300 lx |
| Kitchen — countertops and task areas | 500–750 lx |
| Offices, desk work | 300–500 lx |
| Reading, detailed work | 500–750 lx |
| Retail — general / accent | 300–750 lx, accents 3–5× ambient |
These are horizontal-illuminance conventions for visual tasks. Circadian lighting design uses a different measure entirely — vertical, melanopic-weighted light at the eye — covered in our circadian lighting guide.
Linear Lighting: Lumens per Meter
LED strips and linear systems are rated in lumens per meter (or per foot), which makes area math less obvious: a 1,500 lm/m strip in a 4-meter cove emits 6,000 lm, but an indirect cove bounces that light off the ceiling first, so the lux arriving at the floor is a fraction of what the same lumens would deliver pointed straight down. Geometry, mounting distance, and surface reflectance decide the result — our linear LED lighting guide covers cove and profile design in detail, and our product pages publish per-meter output for every strip and CCT variant.
What Neither Lux nor Lumens Tells You
Both units measure quantity. They say nothing about quality — how faithfully the light renders color. Two 800 lm sources at identical lux can render skin tones, wood, and saturated reds completely differently depending on their spectrum. That's measured by CRI and its deep-red companion R9 — see our high CRI LED guide for when CRI 90, 95, or 98 is worth specifying. And for biological effect, photopic lux undercounts what the circadian system sees: a warm 2700 K source and a cool 6500 K source at the same lux deliver very different melanopic stimulus.
Frequently Asked Questions
How do I convert lumens to lux?
Divide lumens by the area they illuminate in square meters: 3,000 lm spread evenly over 20 m² gives 150 lx. Real installations lose light to absorption and geometry, so measured lux is typically lower than the ideal calculation.
What is a foot-candle?
One foot-candle (fc) is one lumen per square foot, equal to about 10.76 lux. It's the customary illuminance unit in North American practice; specifications often list both.
How many lumens do I need for a room?
Multiply your target lux by the room area in square meters, then allow 1.5–2× for real-world losses. A 20 m² living room at 150 lx needs ~3,000 delivered lumens — roughly 4,500–6,000 installed lumens across ambient and task layers.
Is a higher lumen count always better?
No. Too many lumens in the wrong place produce glare and flat, uncomfortable spaces. Good lighting design layers moderate lumen packages where they're needed — and light quality (CRI, R9, spectrum) is specified separately from quantity.
Are lux and brightness the same thing?
Not exactly. Lux is measurable illuminance on a surface; perceived brightness also depends on surface reflectance, contrast, and how your eyes have adapted. A dark-walled room needs more lux than a white one to feel equally bright.
Method note: illuminance targets above are commonly published design ranges; project-specific requirements (IES recommended practices, EN 12464-1, WELL) take precedence for specification work.