Calculating room lighting: lumens and lux per m²

Multiply the surface area in m² by the recommended lux: allow 3,000 lm for a 15 m² living room (200 lux), 4,500 lm for a 15 m² kitchen (300 lux). Then divide this total by the output of a single source to find the number of light points to distribute.

How do you calculate the lighting needed in a room?

Apply the formula lumens = surface area (m²) × recommended lux. For a 20 m² living room at 200 lux, aim for 4,000 lm in total. Then add up the output of each source, ceiling light, floor lamp and accent lamp, until you reach that figure, rather than relying on a single central point.

Lighting is the set of sources that bring light to a space: the emitted flux is measured in lumens and the received light in lux (1 lux = 1 lumen per m²). The flux is shown on the packaging, never in watts, which only indicate consumption. For a result without dark zones, it is better to choose your light fittings according to their actual output and combine several heights of light.

How do you calculate the total luminous flux?

Add up the lumens of all the sources in the same room to get the total luminous flux. A 15 m² living room at 200 lux requires 3,000 lm: a 1,800 lm pendant plus two 600 lm lamps are enough, without overloading a single point.

How do you calculate illuminance in lux?

Divide the received lumens by the surface area: 4,000 lm over 20 m² gives 200 lux. To size your installation, reverse the formula: desired lux × surface area = lumens to install. A simple reminder to understand lux avoids confusing emitted light with received light.

Why does the received lux differ from the emitted lumens?

The lux measured at floor level is always lower than the emitted lumens, because light disperses and is absorbed. Allow 10 to 15% extra flux per metre above 2.5 m ceiling height, and up to 20% margin with dark walls, which reflect less than light walls.

Once you know your total lumens, you can talk it through with an adviser to distribute these sources without dark zones.

How many lumens per m² depending on the room?

Allow 100 to 200 lux for a living room or bedroom, 300 lux for a kitchen, 300 to 500 lux for an office, and 150 to 200 lux for a dining room. Multiply these lux by the surface area: the same room needs twice as many lumens in a kitchen as in a bedroom.

• 15 m² bedroom, 100 lux: 1,500 lm
• 15 m² living room, 200 lux: 3,000 lm
• 15 m² kitchen, 300 lux: 4,500 lm
• 15 m² office, 400 lux: 6,000 lm

At equal flux, the result depends on the type of source: in a survey of 219 references from our catalogue on 23 September 2026, 79% carry the LED mention, which is more stable in lumens than an old filament bulb.

How many lumens per m² for a dining room?

For a dining room, allow 150 to 200 lux: an 8 m² table in a 12 m² room aims for around 2,400 lm above the tabletop, complemented by softer ambient lighting on the sides.

A dining room chandelier hung 75 to 85 cm above the tabletop concentrates the flux where people eat, without dazzling the guests.

What lighting for a 20 m² room?

A 20 m² room at 200 lux requires 4,000 lm. Distribute them between a central ceiling light and two accent sources rather than a single point, to eliminate cast shadows in the corners.

The flux depends on the bulb: checking which bulb wattage to choose according to the base avoids installing a source that is too weak for the surface area.

How do you calculate the number of ceiling spotlights?

Divide the desired total flux by the flux of one spotlight, then distribute the result on a regular grid. For 4,000 lm with 400 lm spotlights, install 10 spotlights spaced about 1 to 1.5 m apart, 30 cm from the walls to avoid dark zones.

How many spotlights per m²?

Allow on average one 300 to 400 lm spotlight per m² for general lighting, more over a worktop. A 20 m² living room works with 8 to 10 spotlights; a kitchen, which is more demanding, needs a third more.

Choose the flux before the design: LED spotlights with a uniform flux avoid shadow patches between two points.

How many spotlights are needed for 50 m²?

For 50 m² at 200 lux, you need 10,000 lm: around 25 spotlights of 400 lm, or fewer if you combine spotlights and pendants. On a low ceiling, multiply low-flux points rather than using a single powerful light.

Over a large surface area, an LED ceiling light in addition to spotlights raises the general level without multiplying the holes drilled.

How many lumens for outdoor lighting?

Allow 300 to 500 lumens for an entrance or a door, 100 to 200 lumens per path bollard, and 700 to 1,300 lumens to light a terrace. Direct the flux towards the ground to limit glare and unnecessary spill towards the sky.

What LED wattage for outdoor lighting?

An 8 to 15 W LED delivers 800 to 1,500 lumens, enough for most facades. Above all, the protection rating comes first: in our survey of 219 references on 23 September 2026, 84% show an IP20 reserved for dry interiors, whereas outdoor use requires at least IP44, and IP65 in driving rain.

To create coherent terrace outdoor lighting, alternate low-level markers and grazing light on the walls.

How many lumens per room and per space should you plan for?

The right benchmark per room is quick to sum up: around 1,500 lm for a 15 m² bedroom, 3,000 lm for a living room, 4,500 lm for a kitchen, and nearly 100 lm per square metre of hallway or staircase.

If you are unsure about a source, the Designix Google listing gathers buyer feedback on our light fittings.