Lighting, Daylighting & Building Acoustics

Designing for seeing and hearing. Learn photometric quantities (lumen, lux, candela, luminance), recommended illuminance levels, the lumen method with utilisation and maintenance factors, lighting power density, LED efficacy and controls, daylight factor and daylight autonomy, glare, colour temperature and CRI, then acoustics — sound levels in dB, noise criteria, reverberation time with Sabine's formula, absorption coefficients, sound insulation (STC, mass law) and HVAC noise — with Python for luminaires, daylight factor and RT60.

Good lighting lets people work comfortably and efficiently with minimal energy; daylight improves wellbeing and cuts electricity. Good acoustics make classrooms intelligible, offices productive and homes quiet.

Both are quantified and designed with simple, reliable formulas refined by simulation.

An analogy

Lighting design is like watering a garden evenly: you need enough 'light rain' (lux) on every surface, spread by well-placed sprinklers (luminaires). Acoustics is like controlling echoes in a canyon: soft absorbent surfaces soak up sound so speech stays clear.

Light quantities and levels

Recommended maintained illuminance (typical):

Lighting design and daylighting

LEDs (100–180 lm/W) dominate; colour temperature (2700 K warm to 6500 K cool) and CRI (≥ 80, ≥ 90 for retail/art) affect appearance. Controls — occupancy sensors, daylight dimming, scheduling — save 20–60%. Daylighting: windows, light shelves, clerestories and skylights, balanced against glare and solar heat. Metrics: daylight factor, spatial daylight autonomy (sDA), useful daylight illuminance; glare assessed with DGP/UGR.

Room acoustics

Sound level in dB is logarithmic: doubling sources adds 3 dB; +10 dB sounds twice as loud. Reverberation time should suit the use: speech 0.5–0.8 s, concert halls 1.8–2.2 s. Absorbers: porous (mineral wool, acoustic tiles) for mid-high frequencies, panel/membrane absorbers for low frequencies, Helmholtz resonators. Room shape and diffusers control echoes and focusing.

Sound insulation and noise control

Airborne sound insulation depends on mass (mass law: +6 dB per doubling of mass), airtightness and decoupling (double-leaf walls with cavity absorption); ratings STC/Rw. Impact noise from floors is reduced by floating floors and resilient layers. HVAC noise (NC/NR criteria) is controlled with duct silencers, low air velocities and vibration isolation. Simulation (ray tracing, ODEON) supports auditorium design.

Formulas

Worked example: Number of luminaires

Given: 500 lux, 100 m², 4000 lm, UF 0.6, MF 0.8

Find: N.

Answer: 27 luminaires (always round up)

Worked example: Adding sound levels

Given: Two machines, 80 dB each

Find: Total.

Answer: 83 dB

Worked example: RT₆₀

Given: V 500 m³, absorption 100 m²

Find: RT₆₀.

Answer: 0.81 s

Lumen method, daylight factor and reverberation time

import math
# Artificial lighting (lumen method), daylight factor and room acoustics (Sabine)
E, A, UF, MF = 300.0, 60.0, 0.6, 0.8       # lux, m2, utilisation, maintenance
lumens_needed = E * A / (UF * MF)
lamp = 3600.0                                # lm per LED fitting
n = math.ceil(lumens_needed / lamp)
print(f"lumens needed {lumens_needed:.0f} lm -> {n} fittings of {lamp:.0f} lm, LPD {n*36/A:.1f} W/m2 (36 W each)")
# Daylight factor: indoor 450 lux under 15000 lux overcast sky
print(f"daylight factor {450/15000*100:.1f}%")
# Sabine reverberation time for a 10 x 8 x 4 m classroom
V = 10 * 8 * 4
surfaces = [("floor tiles", 80, 0.02), ("ceiling acoustic tile", 80, 0.70), ("walls plaster", 144, 0.03), ("occupants (30)", 30, 0.45)]
Aabs = sum(s * a for _, s, a in surfaces)
print(f"absorption {Aabs:.1f} m2 sabins, RT60 = {0.161*V/Aabs:.2f} s")
# lumens needed 37500 lm -> 11 fittings of 3600 lm, LPD 6.6 W/m2 (36 W each)
# daylight factor 3.0%
# absorption 75.4 m2 sabins, RT60 = 0.68 s

An office needing 300 lux over 60 m² needs 11 LED panels — an LPD of 6.6 W/m², within ECBC limits (~9.5 W/m² for offices). A 3% daylight factor means good daylight for much of the day. The acoustic ceiling gives the classroom an RT₆₀ of 0.68 s — within the 0.6–0.8 s target for speech; without it (α 0.02) RT would exceed 3 s and speech would be unintelligible.

Common mistakes

Applications

Key takeaways

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