Effective height is the vertical distance used for beam-spread geometry.
Effective height is the mounting height minus the assessed plane height. It is a geometry input for beam diameter, not a proof of lux or glare performance.
Technical meaning
Effective height is the vertical distance from the luminaire light-emitting position to the assessed plane.
For simple beam geometry, effective height equals mounting height minus workplane or task-plane height.
Calculation use
Beam diameter uses effective height directly: diameter = 2 x effective height x tan(beam angle / 2).
Downlight spacing and high-bay estimates use effective height to compare beam footprint with nominal centre spacing.
Not the same as
Effective height is not always ceiling height. A bench, desk or shelf plane reduces the vertical distance used in the calculation.
Effective height is not a lux result. It only sets the geometry scale before output, UF, MF and distribution are considered.
Australian context
Australian calculator notes should state both mounting height and task-plane height so downlight, high-bay and beam-spread results are reproducible.
Examples
Example
Value
Planning note
Ceiling to floor
2.4 m - 0 m = 2.4 m
Use when the floor is the assessed plane.
Ceiling to kitchen bench
2.4 m - 0.9 m = 1.5 m
The smaller height gives a smaller beam footprint.
High-bay to workplane
6.0 m - 0.8 m = 5.2 m
Useful for warehouse geometry before maintained-light checks.