Lighting design, controls and energy efficiency
Domain 3: Lighting design, controls and energy efficiency
This domain tests whether a lighting scheme meets visual task needs, energy limits and controllability. The exam looks for correct lumen methods, glare and colour metrics, and controls that actually save energy without compromising safety.
Core rules
- Design to maintained illuminance for the task, with uniformity and glare limits (e.g., UGR) appropriate to the space.
- Calculate luminaire number from required lumens divided by delivered lumens per luminaire, using utilisation factor and maintenance factor.
- Check lighting power density (W/m²) and luminous efficacy (lm/W); do not trade illuminance for a low LPD.
- Use daylight dimming, occupancy sensing, time scheduling and zoning; commission and verify savings.
- Keep emergency lighting on a separate, monitored circuit with correct duration and illuminance.
- Select colour rendering and colour temperature for the task, not only for appearance.
Worked example
An office of 120 m² needs 300 lx. Each LED luminaire delivers 3600 lm; utilisation factor 0.70, maintenance factor 0.80. Delivered lumens per luminaire = 3600 × 0.70 × 0.80 = 2016 lm. Required lumens = 300 × 120 = 36,000 lm. Number = 36,000/2016 = 17.9, so use 18 luminaires. At 36 W each, LPD = 18 × 36/120 = 5.4 W/m². Check uniformity and glare after layout.
Traps
- Using initial lumens without maintenance factor.
- Calculating lux from total lumens without room area and utilisation.
- Claiming controls savings without commissioning.
- Confusing emergency lighting with normal lighting.