Key objectives in Lighting design Visual performance Physiological conditions Visual quality no strong "contrasts" good "color rendering" adequate "light levels" no "disturbing reflections" no direct "glare"
Radiometry vs. Photometry absolute (energy) vs. V(λ)-dependent (light) Relative Efficiency [-] 1.0 0.9 0.8 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.
Radiometry vs. Photometry absolute (energy) vs. V(λ)-dependent (light) Relative efficiency [-] 1.0 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.
Four major quantities flux illuminance intensity luminance Image by MIT OCW.
energy / unit of time φ in Watts [W] vs. lumen [lm] Image by MIT OCW.
energy / unit of time φ in Watts [W] vs. lumen [lm] 683 lumen/watt at 555 nm : φ lum [lm] = 683 Σ V(λ) φ e [W] Incandescence 75 watts Discharge 70 watts very different efficacies! 1055 lumens Images by MIT OCW. 5600 lumens
flux received / unit of surface E in [W/m 2 ] vs. [lm/m 2 ] or lux [lx] φ S Images by MIT OCW.
flux received / unit of surface E in [W/m 2 ] vs. [lm/m 2 ] or lux [lx] Full moon Overcast sky Sunlight 0.01 Lux 8'000-20'000 Lux 100'000 Lux Image by MIT OCW.
flux received / unit of apparent surface (cosine ("Lambert") law) E in [W/m 2 ] vs. [lm/m 2 ] or lux [lx] α E = φ S Eα = E. cos α Images by MIT OCW.
flux received / unit of apparent surface (cosine ("Lambert") law) E in [W/m 2 ] vs. [lm/m 2 ] or lux [lx] 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
flux received / unit of apparent surface (cosine ("Lambert") law) E in [W/m 2 ] vs. [lm/m 2 ] or lux [lx] measurement with lux-meter (illumance-meter) exitance M for emitted flux [lux]
Intensity flux emitted "in a certain direction" φ Ω Images by MIT OCW.
Intensity flux emitted within a certain solid angle d A = Ω. d 2 A Ω = d 2 A Ω Images by MIT OCW.
Intensity flux emitted within a certain solid angle I in [W/sr] vs. [lm/sr] or Candela [Cd] 1 Candela = intensity of one candle
Intensity flux emitted within a certain solid angle I in [W/sr] vs. [lm/sr] or Candela [Cd] inverse square law for point source E = I cos(θ) / d 2 θ d Image by MIT OCW.
Intensity 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 270 o 240 o 120 o 90 o 300 o 100 200 60 o 330 o 300 400 30 o Image by MIT OCW.
105 o Radio- and photometric quantities Intensity 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 180 o 165 o 150o 135 o 120o 30 90 o 40 h = 10 ft d 60 80 100 120 140 160 180 200 0 o 15 o 30o 45 o 60 o 75 o 180 cd Image by MIT OCW.
Source N s θ Ω φ Intensity I Luminance S s flux emitted by apparent surface in a given direction I/m 2 (or M/sr) L in [Cd/m 2 ] Images by MIT OCW.
Intensity Luminance flux emitted by apparent surface in a given direction I/m 2 (or M/sr) L in [Cd/m 2 ] S S a L = I / S a L = I / (S. cos θ) θ
Intensity Specular Spread Diffuse Luminance flux emitted by apparent surface in a given direction I/m 2 (or M/sr) L in [Cd/m 2 ] Diffuse/Specular Specular/Spread Diffuse/Spread Intensity variation Image by MIT OCW. Luminance variation lambertian surface lambertian surface
Intensity Luminance Radio- and photometric quantities flux emitted by apparent surface in a given direction I/m 2 (or M/sr) L in [Cd/m 2 ] Primary sources Sun Incandescent lamp (100 W, bright) Incandescent lamp (100 W, frosted) Fluorescent tube (40 W, 38 mm) Candle Computer screen Cd/m 2 1 650 000 000 6 000 000 125 000 5000-8000 5000 100-200
Intensity Luminance Radio- and photometric quantities flux emitted by apparent surface in a given direction I/m 2 (or M/sr) L in [Cd/m 2 ] 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) Cd/m 2 2 500-3000 100 50 5 Minimal luminance perceived: 10-5
Luminance measurement Eye = luminance-meter
Photometry Reading assignment from Textbook: Introduction to Architectural Science by Szokolay: 2.1 Additional readings relevant to lecture topics: "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