How many site lights do I need? Lighting calculator
Multiply the area in square metres by the light level you need in lux, then divide by the useful lumens from each light. HSE guidance (HSG38) suggests about 20 lux average for walkways and traffic routes, 50 lux on construction sites and loading bays, 100 lux for general work and 200 lux for detailed work. Our calculator does the sums for 2ft site fittings, bulkheads, floodlights and rope light (strip light).
Lighting calculator
Turn on JavaScript to use the calculator, or use the formula below.
Recommended light levels (HSE HSG38)
| Activity | Average | Minimum |
|---|---|---|
| Movement of people, machines and vehicles (walkways, traffic routes) | 20 lux | 5 lux |
| Movement in hazardous areas (construction sites, loading bays) | 50 lux | 20 lux |
| Work needing limited perception of detail | 100 lux | 50 lux |
| Work needing perception of detail (offices) | 200 lux | 100 lux |
How it works: the lumen method
Number of lights = lux × area ÷ (lumens per light × UF × MF)
- UF (utilisation factor) is the share of light that reaches the working area. Bare concrete and open floors waste a lot, so we use 0.5 indoors and 0.4 outdoors.
- MF (maintenance factor) allows for dirt and ageing. We use 0.8.
Worked example
A 30m × 20m floor (600m²) at 50 lux needs 50 × 600 ÷ 0.4 = 75,000 lumens from the fittings. With 2ft site fittings at 3,200 lm each, that's 24 fittings: about 650W, or 5.9A at 110V.
Emergency lighting
Escape routes also need light that stays on in a power cut. See how to light a stairwell for emergency festoon, emergency rope light (strip light) and emergency site fittings.
Want a layout?
The calculator gives a quick estimate. For a whole building, send us the floor plans and we'll suggest the kit and the layout.
