Lighting, Acoustics, and Environmental Comfort
This domain tests the invisible systems that make a room usable: layered illumination, color quality, sound isolation and absorption, and thermal comfort.
Core rules
- Layer ambient, task, and accent light on separate controls. Target illuminance: 10-20 fc ambient in living areas, 30-50 fc on kitchen counters and desks, 50-75 fc for detailed tasks, 5-10 fc for nighttime circulation.
- Color: CRI 90+ for residential work; 2700-3000 K in living and dining, 3000-3500 K in kitchen and bath; keep CCT consistent within sight lines and confirm dimmer compatibility (TRIAC, 0-10 V, DALI).
- Downlight spacing is roughly 0.8-1.2 times the mounting height above the work plane for even coverage.
- Acoustics: STC 50+ for party walls, IIC 50+ for floors, NRC 0.6-0.8 for absorptive ceilings; aim for 0.4-0.6 s reverberation in living spaces using Sabine: RT60 = 0.049 V / A.
- Comfort: stay inside the ASHRAE 55 range, 68-75 F and 30-60% relative humidity; keep supply registers off seating; limit radiant asymmetry (tightest for warm ceilings, about 5 C / 9 F).
Worked example
A 2,000 cu ft living room with 300 sabins of absorption: RT60 = 0.049 x 2,000 / 300 = 0.33 s, which is dead for conversation. Adding a rug, drapes, and an upholstered chair to reach 200 sabins gives 0.49 s - livelier for music and still intelligible. For lighting, a 192 sq ft kitchen at 35 fc needs 6,720 delivered lumens; with a coefficient of utilization of 0.7 and maintenance factor 0.8, that is 6,720 / 0.56 = 12,000 lamp lumens, about fifteen 800-lumen downlights plus undercabinet task light.
Traps
- Treating lamp lumens as delivered footcandles; apply utilization and maintenance factors.
- Mixing 4000 K lamps into a warm palette.
- Fixing echo with absorption on one surface only while parallel reflections remain.
- Specifying a bath fan without a duct path or makeup air.