A floodlight that lights a car park well can also light the bedroom next door. AS/NZS 4282:2023 sets limits on that spill light at the boundary. This guide checks one small car park with the obtrusive light tool, then changes the lights until they pass. The zones and the three limits are explained in Obtrusive light and the 4282 zones.
The tool is a point-source estimate. It stands in for a photometric calculation while you choose luminaires and aiming. A site measurement or the maker's photometric file rules.
The site
- A shop car park on the edge of a small town. The houses behind it are in zone A2.
- Two 10 000 lm LED floodlights on one 6 m pole, beam angle 90°.
- Each floodlight tilts 30° from straight down, toward the houses.
- The pole is 10 m from the rear boundary. A bedroom window faces the car park, its centre 1.5 m above the ground at the boundary.
- The maker's data gives an upward fraction of 0.02 at that tilt.
- The lights stay on until 10 p.m. They do not run in the curfew.
Step 1. Pick the zone and the period
The zone is the zone of the area that receives the light: here the houses, in A2. Table 3.2 sets 5 lx at the window outside the curfew and 1 lx in it. Table 3.3 sets 7 500 cd per luminaire outside the curfew at Level 1, and 1 000 cd in it. The upward light ratio limit for A2 is 0.01.
The curfew runs from 11 p.m. to 6 a.m. unless the council sets other hours. These lights switch off at 10 p.m., so the non‑curfew limits apply.
Step 2. Work the light at the window
Open the tool: its defaults are this car park. For each floodlight it builds a beam whose intensity halves at 45° off the axis. A 90° beam gives a peak of 4 775 cd. The window sits about 36° off the beam axis, so each floodlight sends 3 143 cd toward it.
The window is 11 m from the floodlights in a straight line. One floodlight gives 23.84 lx on the vertical glass, and the two give 47.67 lx. The calculation uses initial lumens, a maintenance factor of 1.0 (Cl 3.2.2).
| Check | Result | Limit (A2, non‑curfew) | State |
|---|---|---|---|
| Vertical illuminance | 47.67 lx | 5 lx | Fails |
| Luminous intensity | 3 143 cd | 7 500 cd | Passes |
| Upward light ratio | 0.02 | 0.01 | Fails |
The window gets nearly ten times its limit. The tilt also puts light above the horizontal.
Step 3. Aim the floodlights straight down
Set the tilt to 0° and pick a full cut-off model, upward fraction 0. The beam now points at the ground below the pole. The window is 66° off the axis, and each floodlight sends 804 cd toward it.
The window gets 12.2 lx. The upward light ratio passes at 0, but the illuminance still fails.
Step 4. Use a narrower beam
Keep the floodlights aimed down and change to a 60° optic. The intensity at 66° off the axis falls to 127 cd, and the window gets 1.92 lx. All three checks pass outside the curfew. Check the 60° floodlights in the tool.
A narrower beam lights a smaller area of the car park. Check the lighting level on the ground with the maker's layout software before you order.
Step 5. If the lights run in the curfew
Turn on the curfew. The limit at the window falls to 1 lx, and the 60° floodlights fail at 1.92 lx. A 40° optic aimed down passes at about 0.01 lx. Dimming or switching the floodlights off at 11 p.m. also works, and a timer is the cheaper fix.
The result
| Change | Ev at the window | Intensity | ULR | Non‑curfew |
|---|---|---|---|---|
| 90°, tilted 30° | 47.7 lx | 3 143 cd | 0.02 | Fails |
| 90°, aimed down, full cut-off | 12.2 lx | 804 cd | 0 | Fails |
| 60°, aimed down, full cut-off | 1.92 lx | 127 cd | 0 | Passes |
The floodlights also need a circuit. Two 80 W LED floodlights draw under 1 A, so the cable size tool sets the cable by the voltage drop on a long run to the pole.
See also: Obtrusive light and the 4282 zones, Lighting circuit loop impedance, B curve 10 A and Homeowner shed supply voltage drop over 60 m.