Lighting Layout Basics
Spacing, uniformity and the lumen method.
1. Why it matters
A lighting layout turns a target illuminance into a fixture count and spacing that actually delivers it on the working plane — evenly, without dark gaps or glare. Get the layout right and you buy fewer fixtures that light the space correctly; get it wrong and you either over-spend on lumens or hand the client a room that fails its lux requirement on day one.
2. Start from the required illuminance
Every layout begins with the maintained illuminance the task needs, taken from a standard such as EN 12464-1 (Europe) or the IES Handbook (North America). Design to the maintained value, applying a maintenance factor (typically 0.7-0.8) so the space still meets target at end of life, not just when new.
| Space | Typical maintained lux |
|---|---|
| Warehouse aisles / storage | 150-200 lx |
| General office / open plan | 300-500 lx |
| Detailed / drawing work | 750-1000 lx |
| Retail sales floor | 300-750 lx (+ accent) |
| Car park / circulation | 75-100 lx |
3. Spacing, mounting height and uniformity
Spacing is not free — it is bounded by the fixture's spacing-to-height ratio (SHR / SHRmax). Exceed it and you get scallops of light and dark between fixtures even if the average lux is fine. Uniformity (Emin/Eavg) is the real quality metric.
- Keep centre-to-centre spacing ≤ SHRmax × (mounting height above the working plane).
- Target uniformity Emin/Eavg ≥ 0.6 for task areas, ≥ 0.4 for surrounds.
- Half-spacing from the walls to avoid dark perimeters.
- Higher mounting needs narrower beams; low ceilings need wide/batwing optics.
4. Glare, and a quick sanity check
Control glare with UGR (Unified Glare Rating): aim UGR ≤ 19 for offices and screen work, ≤ 22 for industry, ≤ 25 for rough tasks. Before trusting any software, sanity-check fixture count with the lumen method: fixtures ≈ (target lux × area) ÷ (lumens per fixture × utilisation factor × maintenance factor). It will not place the fixtures, but it tells you instantly if a quote's quantity is plausible or padded.
5. Checklist
- Set the maintained target lux from EN 12464-1 / IES
- Apply a maintenance factor (0.7-0.8) to design values
- Keep spacing within the fixture SHRmax
- Check uniformity Emin/Eavg, not just average lux
- Hold UGR to the space limit; sanity-check count with the lumen method