Table PDFLighting Calculation Formulas Table

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Calculation	Formula	Use	Boundary
Known lumens to lux	lux = lumens x UF x MF / area	Check a scheduled output group against the area and task plane it serves.	Average lux does not prove uniformity, glare or measured performance.
Lux target to lumens	lumens = target lux x area / (UF x MF)	Turn a maintained target into a lumen allowance for one assessed zone.	The target lux and plane must come from the brief or a suitable reference.
How many fittings	fittings = ceiling(required lumens / lumens per fitting)	Round a lumen allowance into a schedule quantity for one luminaire output.	Rounding can change symmetry, spacing, overshoot and glare conditions.
Lighting connected load	watts = fitting count x watts per fitting	Summarise the input load for one lighting group before energy comparison.	Connected load is not electrical circuit design.
Annual running energy	kWh/year = watts / 1000 x hours/day x days/year	Estimate annual lighting energy from load and operating schedule.	Cost depends on the user-entered tariff, not a site tariff claim.
Beam spread or footprint	diameter = 2 x effective height x tan(beam angle / 2)	Estimate the beam footprint at the assessed plane before spacing review.	Beam geometry is not a lux, glare or spill-light assessment.
Daylight factor	daylight factor = indoor lux / outdoor lux x 100	Compare indoor daylight with the same-condition outdoor reference.	Daylight varies with sky condition, orientation, glazing and shading.
Daylight remaining target	remaining lux = target lux - daylight contribution	Show how much of the target still needs artificial lighting.	Do not treat a momentary daylight reading as an all-day design result.

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