Outdoor lighting is obtrusive when it lights more than its own site. It can shine into a bedroom, dazzle a driver, or brighten the night sky. AS/NZS 4282:2023 sets limits for each of these, and a council can make them a condition of consent.
The obtrusive light tool checks three of the limits at one window. The worked guide Car-park floodlight: obtrusive light at a boundary takes one car park from a fail to a pass.
The environmental zones
The limits depend on how dark the area is already. Table 3.1 sorts places into five zones, from the darkest to the brightest, plus a zone for TV stadiums.
| Zone | Ambient light | In practice |
|---|---|---|
| A0 | Intrinsically dark | Dark-sky reserves and observatories |
| A1 | Dark | Remote countryside |
| A2 | Low district brightness | Rural and semi-rural houses |
| A3 | Medium district brightness | Suburbs |
| A4 | High district brightness | Town centres, commercial and industrial land |
The zone follows the planning zoning of the area that receives the light, future zoning included. Where the zone is unclear, ask the council.
The curfew
Each zone has two sets of limits for the light at a window and for intensity. The higher set applies in the evening. The lower set applies during the curfew, which runs from 11 p.m. to 6 a.m. unless the council sets other hours (Cl 3.2.4). Lighting that runs all night must meet the curfew limits.
Light at the window: Ev
The first limit is the vertical illuminance, Ev, in lux on the plane of a window. AS/NZS 4282 calculates it at the centre of each habitable-room window that can see the lights (Cl 3.3.1.3). With no house yet, it uses a grid on a vertical plane at the boundary.
Only direct light counts, with a maintenance factor of 1.0. In A2 the limit is 5 lx in the evening and 1 lx in the curfew. For a sense of scale, a full moon gives well under 1 lx.
Glare: intensity per luminaire
The second limit is the luminous intensity, in candela, of each luminaire toward the window. It limits glare: a bright point in the view even when the room gets little light. Outside the curfew Table 3.3 gives two levels. Level 1 applies to new lighting. Level 2 needs a precedent from existing lighting nearby (Cl 3.2.5).
A floodlight tilted up toward the houses has a high intensity toward them. The same floodlight aimed straight down shows the window only the edge of its beam.
Sky glow: the upward light ratio
The third limit is the upward light ratio, ULR: the lumens that leave above the horizontal, divided by all the lumens of the installation (Cl 3.3.1.8.2). It applies to the whole installation, so one luminaire can exceed it if the rest make up for it. In A0 and A1 the limit is 0, so every luminaire must be full cut-off.
A full cut-off luminaire mounted level sends nothing above the horizontal. Tilting it up changes that, so take the upward fraction from the maker's data at the installed tilt.
How the tool estimates
The tool treats each row of luminaires as one point with a smooth beam. The intensity falls with the angle from the beam axis, halving at half the beam angle. It is the same beam model as the plan's light layer. The tilt turns the beam toward the boundary. The tool then works the intensity toward the window and the illuminance on the vertical glass.
That makes it an estimate. A real luminaire has its own intensity table, and a site has walls, fences and trees between the light and the window. Use the tool to choose the luminaire, the aiming and the pole position. Then confirm with a photometric calculation or a site measurement.
What the tool leaves out
- Threshold increment, the glare limit for drivers on a nearby road.
- Signs, facades and artwork, which have their own luminance limits in Table 3.4.
- Public road lighting, which Section 4 of the standard covers.
- Obstructions, reflections and Level 2 intensity.
See also: Car-park floodlight: obtrusive light at a boundary, Lighting circuit loop impedance, B curve 10 A and Damp situations: the Section 6 zones.