Home & Construction⏱ 4 min read
How to Calculate the Right Amount of Lighting for a Room
Lumens, not watts, is what matters for lighting. Here is how to calculate how many lumens your room needs, what colour temperature to choose, and how to position lights correctly.
The shift from incandescent to LED lighting broke the old "60W per room" rules. Lumens -- the measure of actual light output -- is what you need to calculate, and the requirements vary significantly by room function.
Recommended Lumens per Square Metre
Lux = lumens per square metre (illuminance)
General rule: Lumens needed = Room area (m2) x Recommended lux
Recommended lux levels by room type:
Living room (general): 150-300 lux
Kitchen (general): 300 lux
Kitchen (work surfaces): 500 lux
Bathroom: 300 lux (vanity area: 500-700 lux)
Bedroom: 100-200 lux (bedside reading: 300-500 lux)
Home office: 400-500 lux
Hallways/stairs: 100-150 lux
Garage/utility: 300-400 lux
Calculating Lumens for a Room
Living room: 4m x 5m = 20 m2
Target: 200 lux (mid-range for living room)
Total lumens needed: 20 x 200 = 4,000 lumens
But: ceiling height and reflectance affect actual illuminance.
Efficiency factor (room surface reflectance):
Light colours, low ceiling (2.4m): efficiency factor 0.50-0.60
Medium colours, average ceiling: efficiency factor 0.40-0.50
Dark colours, high ceiling: efficiency factor 0.25-0.35
Adjusted lumens: Required lumens / Efficiency factor
At efficiency 0.50: 4,000 / 0.50 = 8,000 lumens total
(This is the bulb output needed, not the room illuminance)
Watts to Lumens Conversion (LED)
LED WattsLumens (approx)Old incandescent equiv.
4-5W400-500 lm40W incandescent
6-8W600-800 lm60W incandescent
9-11W900-1,100 lm75W incandescent
12-15W1,200-1,500 lm100W incandescent
18-20W1,800-2,000 lm150W incandescent
Colour Temperature Selection
Colour temperature (Kelvin) affects the feel of a space:
2,700K (warm white): relaxing, amber-toned
Best for: living rooms, bedrooms, dining rooms
3,000K (soft white): slightly brighter than warm
Best for: bathrooms, kitchens (residential)
4,000K (cool white): neutral, clinical feel
Best for: kitchens, home offices, garages
5,000-6,500K (daylight): blue-toned, alerting
Best for: task lighting, workshops, reading lamps
Consistency matters: mixing 2,700K and 4,000K in the same room
creates an uneasy visual tension. Choose one temperature per space.