Room Lighting Calculator

Room area, m²

Purpose

Output per lamp, lm

Lamp type

Ceiling height, m

Result

Lamps needed4
Flux required, lm2,700
Target illuminance, lx150
Total wattage, W27
Watts per m²1.5
Height correction1

From what the room is for to how many fittings

Works out the luminous flux a room needs for its purpose, how many lamps that means and the total wattage, with a ceiling-height correction.

Every room has its own target: a bedroom is fine at a hundred lux, a kitchen wants three hundred, a study five hundred and a workshop seven hundred and fifty. Multiply the target by the floor area and you have the flux the room needs.

High ceilings eat light. Illuminance falls with the square of distance, so a three-and-a-half metre ceiling needs about half as much flux again for the same result. The calculator applies that correction for you.

What this calculator shows

The recommended illuminance for the room type you pick
Total flux required and how many lamps of your chosen output that is
Total wattage and the load per square metre

What to keep in mind

Targets follow EN 12464, the European workplace lighting standard that national codes are built on.
Reflection from walls and ceiling is not modelled; in dark interiors add roughly a third.

FAQs

How many watts of lighting per square metre?

One and a half to two watts of LED in a living room, three to four in a kitchen. The old rule of twenty watts per square metre referred to filament lamps and is meaningless now.

One bright lamp or several dimmer ones?

Several. A single fitting throws hard shadows and glares; spreading them across the ceiling gives even light. Task lighting is then added where people read or cook.

How do I allow for dark walls?

Add 30 to 50 percent. Light ceilings and walls act as reflectors and lift illuminance noticeably; dark ones absorb it.

What colour temperature should I choose?

2700-3000 K for bedrooms and living rooms, 4000 K for kitchens and bathrooms, 5000-6500 K for studies and workshops. It does not change the lamp count but transforms how the room feels.

Worked example

An eighteen-metre living room

Input: 18 m², living room, 800 lm lamps, 2.7 m ceiling

Output: 2,700 lm needed — 4 lamps, 27 W of LED

Note: Twenty-seven watts over eighteen square metres is 1.5 W per square metre. The same job in filament lamps would have taken 225 watts.

Useful links

All tools in Electrical

Room Lighting Calculator

Result

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