Utilisation factor is a delivery assumption for how much light reaches the assessed plane.
Utilisation factor, or UF, is an estimate of the luminaire output that reaches the assessed plane. It is a delivery assumption, not a substitute for photometric design.
Technical meaning
Utilisation factor is the assumed fraction of luminaire output that contributes to illuminance on the assessed plane.
UF is affected by luminaire distribution, room proportions, surface reflectance, mounting layout and obstructions.
Calculation use
In lumen-method estimates, required lumens increase as UF decreases: required lumens = target lux x area / (UF x MF).
UF is used as a delivery allowance in room, workplace and warehouse estimates before fixture count is rounded.
Not the same as
UF is not a fixed Australian standard value. Generic bands are placeholders until photometry and room conditions are known.
UF is not maintenance factor. UF describes light delivery to the plane; MF describes loss over time and maintenance conditions.
Australian context
Australian planning notes should name UF as an assumption and keep it beside the source route or project method that justified the value.
Examples
Example
Value
Planning note
Bright simple room
UF 0.80
Only suitable when optical data and room surfaces support efficient delivery.
Ordinary interior estimate
UF 0.70
Common early allowance for calculator sensitivity, not a design certificate.
Difficult delivery
UF 0.50
Raises the lumen allowance and may indicate layout or fitting selection needs review.
This site explains UF as a calculation input. It does not reproduce hidden method tables or certify that a selected UF satisfies AS/NZS lighting design requirements.