How to Calculate How Many Lights You Need
Room-by-room guide to calculating the right number of downlights, pendants and other fittings for residential and commercial spaces in South Africa.
Measure your room
Calculate the floor area in square metres (length x width). For example, a room that is 5m x 4m = 20 m². For irregularly shaped rooms, break the space into rectangles and add the areas together.
Determine the recommended lux level
Lux measures the amount of light hitting a surface. Different rooms need different lux levels: Living rooms and bedrooms: 150-300 lux. Kitchens and bathrooms: 300-500 lux. Offices and workspaces: 400-500 lux. Retail and showrooms: 500-750 lux. Garages and workshops: 300-500 lux.
Calculate total lumens needed
Multiply the room area by the recommended lux level. For a 20 m² kitchen at 400 lux: 20 x 400 = 8,000 lumens total. For a 15 m² bedroom at 200 lux: 15 x 200 = 3,000 lumens total.
Divide by lumens per fitting
Check the lumen output of your chosen fitting. A typical 5W LED GU10 produces about 400 lumens. For the kitchen example: 8,000 / 400 = 20 downlights. A typical LED panel light produces 3,600 lumens: 8,000 / 3,600 = 3 panels (rounded up). This gives you the minimum number of fittings needed.
Plan your layout
Space downlights evenly in a grid pattern. Keep them at least 600mm from walls and 900-1200mm apart. For rectangular rooms, align them with the longer axis. For open-plan living areas, consider zoning different areas with separate circuits so you can control each zone independently.
Account for task and accent lighting
The lux calculation gives you general ambient lighting. You may also want: Task lighting — under-cabinet strips in kitchens, desk lamps in offices. Accent lighting — wall washers, picture lights, LED strips in shelving. These supplement the general lighting and are calculated separately.
Comparison Table
| Room Type | Recommended Lux | Example: 20m² Room (LED GU10 @ 400lm) |
|---|---|---|
| Bedroom | 150-300 lux | 8-15 downlights |
| Living room | 150-300 lux | 8-15 downlights |
| Kitchen | 300-500 lux | 15-25 downlights |
| Bathroom | 300-500 lux | 15-25 downlights |
| Office | 400-500 lux | 20-25 downlights |
| Garage | 300-500 lux | 15-25 downlights |