How many light fittings can go on a 6A circuit?

A 6A lighting circuit can handle up to 1,380W (6A x 230V). With a standard 66% diversity factor, the effective capacity is around 910W. For 10W LED downlights, that is around 90 fittings in theory, though in practice most electricians limit a single circuit to 10-12 fittings for practical and safety reasons.

What lux level do I need for different rooms?

CIBSE recommends: 150 lux for general residential lighting (living rooms, bedrooms), 300 lux for task areas (kitchens, bathrooms, utility rooms), and 500 lux for detailed work (home offices, workshops, reading areas). Commercial spaces may require higher levels.

What is the diversity factor for lighting?

The diversity factor (typically 0.66 or 66%) accounts for the fact that not all lights on a circuit will be on simultaneously. BS 7671 allows a 66% diversity factor for lighting circuits in domestic installations when calculating maximum demand.

How do I estimate cable runs for lighting?

Cable runs depend on the room layout, fitting positions, and switch locations. As a rough guide, allow 3-4 metres per fitting for the loop between fittings, switch drops, and connections to the consumer unit. Always measure actual routes for final cable ordering.

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Lighting Circuit Calculator — Light Fittings Per Circuit

Calculate how many light fittings fit on a circuit. Work out fittings needed, total wattage, circuits required, and cable run estimates for UK electrical installations.

Room Area

Total surface area to cover

Lux Level RequiredSelect the lux level required for your calculation

Fitting Wattage

Wattage per light fitting

Circuit RatingSelect the current or target rating

How We Calculate This

This calculator determines how many light fittings are needed for a room based on the required lux level, then works out how many lighting circuits are needed to serve them.

Fittings calculation

Total lumens = (Lux x Area) / (Utilisation Factor x Maintenance Factor)

Fittings needed = Total lumens / Lumens per fitting

Circuit calculation

Circuit capacity (W) = Rating (A) x 230V x Diversity factor

Circuits required = Total wattage / Circuit capacity

Defaults

Utilisation factor: 0.6 (typical domestic room)
Maintenance factor: 0.8 (adjustable)
Diversity factor: 0.66 (BS 7671 domestic lighting)
LED efficacy: ~100 lumens per watt

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.