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Key objectives in Lighting design Visual performance Physiological conditions Visual quality ƒ ƒ ƒ ƒ ƒ no strong "contrasts" good "color rendering" adequate "light levels" no "disturbing reflections" no direct "glare" Radio- and photometric quantities Radiometry vs. Photometry 1.0 0.9 0.8 Relative Efficiency [-] ƒ absolute (energy) vs. ƒ V(λ)-dependent (light) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 350 400 450 500 550 600 650 700 750 800 Wavelength [nm] Image by MIT OCW. Radio- and photometric quantities Radiometry vs. Photometry ƒ absolute (energy) vs. ƒ V(λ)-dependent (light) 1.0 Relative efficiency [-] 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 350 400 450 500 550 600 650 700 750 800 Wavelength (nm) Image by MIT OCW. Radio- and photometric quantities Four major quantities ƒ ƒ ƒ ƒ flux illuminance intensity luminance Image by MIT OCW. Radio- and photometric quantities Flux ƒ energy / unit of time ƒ φ in Watts [W] vs. lumen [lm] Image by MIT OCW. Radio- and photometric quantities Flux ƒ energy / unit of time ƒ φ in Watts [W] vs. lumen [lm] ƒ 683 lumen/Watt at 555 nm : φlum [lm] = 683 • Σ V(λ) • φe [W] Incandescence Discharge 70 watts 75 watts very different efficacies ! 1055 lumens Images by MIT OCW. 5600 lumens Radio- and photometric quantities Flux Illuminance ƒ flux received / unit of surface ƒ E in [W/m2] vs. [lm/m2] or lux [lx] ∆φ ∆S Images by MIT OCW. Radio- and photometric quantities Flux Illuminance ƒ flux received / unit of surface ƒ E in [W/m2] vs. [lm/m2] or lux [lx] Full moon 0.01 Lux Overcast sky Sunlight 8'000 - 20'000 Lux 100'000 Lux Image by MIT OCW. Radio- and photometric quantities Flux Illuminance ƒ flux received / unit of apparent surface (cosine ("Lambert") law) ƒ E in [W/m2] vs. [lm/m2] or lux [lx] a E⊥ = ∆φ ∆S Eα = E⊥. cos α Images by MIT OCW. Radio- and photometric quantities Flux Illuminance ƒ flux received / unit of apparent surface (cosine ("Lambert") law) ƒ E in [W/m2] vs. [lm/m2] or lux [lx] ƒ measurement with lux-meter (illumance-meter) Requirements Lux Examples Low 20-70 Circulation, stairs Moderate 120-185 Entrance, restaurant Medium 250-375 General tasks High 500-750 Reading, Writing Very high > 1000 Precision tasks Radio- and photometric quantities Flux Illuminance ƒ ƒ ƒ ƒ flux received / unit of apparent surface (cosine ("Lambert") law) E in [W/m2] vs. [lm/m2] or lux [lx] measurement with lux-meter (illumance-meter) exitance M for emitted flux [lux] Radio- and photometric quantities Flux Illuminance Intensity ƒ flux emitted "in a certain direction" ∆φ ∆Ω Images by MIT OCW. Radio- and photometric quantities Flux Illuminance Intensity ƒ flux emitted within a certain solid angle ∆A = ∆Ω.d2 ∆A ∆Ω = 2 d d ∆A ∆Ω Images by MIT OCW. Radio- and photometric quantities Flux Illuminance Intensity ƒ flux emitted within a certain solid angle ƒ I in [W/sr] vs. [lm/sr] or Candela [Cd] 1 Candela = intensity of one candle Radio- and photometric quantities Flux Illuminance Intensity ƒ flux emitted within a certain solid angle ƒ I in [W/sr] vs. [lm/sr] or Candela [Cd] ƒ inverse square law for point source E = I cos(θ) / d2 q d Image by MIT OCW. Radio- and photometric quantities Flux Illuminance Intensity ƒ ƒ ƒ ƒ flux emitted within a certain solid angle I in [W/sr] vs. [lm/sr] or Candela [Cd] inverse square law for point source intensity distribution 240o 120o 270o 90o 100 300o o 200 60 300 400 o 330 30o Image by MIT OCW. Radio- and photometric quantities Flux Illuminance Intensity 180o o 105 o 120 o 13 o 5 165 o flux emitted within a certain solid angle I in [W/sr] vs. [lm/sr] or Candela [Cd] inverse square law for point source intensity distribution 150 o 90 30° 40 75 o 60 80 100 60 o d 120 140 180 cd 160 o h = 10 ft 45 ƒ ƒ ƒ ƒ 180 o 200 o 0 o 15 30 Image by MIT OCW. Radio- and photometric quantities Flux Ns Source Illuminance Intensity Luminance θ ∆Ω ∆φ ∆I ∆Ss ƒ flux emitted by apparent surface in a given direction ƒ ≈ I/m2 (or M/sr) ƒ L in [Cd/m2] Images by MIT OCW. Radio- and photometric quantities Flux Illuminance Intensity Luminance ƒ flux emitted by apparent surface in a given direction ƒ ≈ I/m2 (or M/sr) ƒ L in [Cd/m2] L = I / Sa L = I / (S . cos θ) S Sa θ Radio- and photometric quantities Flux Illuminance Specular Spread Diffuse Specular/Spread Diffuse/Spread Intensity Luminance ƒ flux emitted by apparent Diffuse/Specular surface in a given direction ƒ ≈ I/m2 (or M/sr) Intensity variation ƒ L in [Cd/m2] lambertian surface Image by MIT OCW. Luminance variation lambertian surface Radio- and photometric quantities Flux Illuminance Intensity Luminance Cd/m2 Primary sources • Sun 1 650 000 000 • Incandescent lamp (100 W, bright) 6 000 000 • Incandescent lamp (100 W, frosted) 125 000 • Fluorescent tube (40 W, 38 mm) 5000 - 8000 • Candle 5000 • Computer screen 100-200 ƒ flux emitted by apparent surface in a given direction ƒ ≈ I/m2 (or M/sr) ƒ L in [Cd/m2] Radio- and photometric quantities Flux Illuminance Intensity Secondary sources • Moon • White paper (ρ = 0.8, E = 400 lux) • Grey paper (ρ = 0.4, E = 400 lux) • Black paper (ρ = 0.01, E = 400 lux) Minimal luminance perceived: Luminance ƒ flux emitted by apparent surface in a given direction ƒ ≈ I/m2 (or M/sr) ƒ L in [Cd/m2] Cd/m2 2 500 - 3000 100 50 5 10-5 Radio- and photometric quantities Luminance measurement ƒ Eye = luminance-meter Photometry Reading assignment from Textbook: ƒ “Introduction to Architectural Science” by Szokolay: § 2.1 Additional readings relevant to lecture topics: ƒ "IESNA Lighting Handbook" (9th Ed.): pp. 2-1 to 2-3 + pp. 3-1 to 3-5 + pp. 3-9 to 3-14 + pp. 4-1 to 4-6