Key objectives in Lighting design

Transcription

1 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"

2 Radiometry vs. Photometry absolute (energy) vs. V(λ)-dependent (light) Relative Efficiency [-] Wavelength [nm] Image by MIT OCW.

3 Radiometry vs. Photometry absolute (energy) vs. V(λ)-dependent (light) Relative efficiency [-] Wavelength (nm) Image by MIT OCW.

4 Four major quantities flux illuminance intensity luminance Image by MIT OCW.

5 energy / unit of time φ in Watts [W] vs. lumen [lm] Image by MIT OCW.

6 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 lumens

7 flux received / unit of surface E in [W/m 2 ] vs. [lm/m 2 ] or lux [lx] φ S Images by MIT OCW.

8 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.

9 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.

10 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 Circulation, stairs Moderate Entrance, restaurant Medium General tasks High Reading, Writing Very high > 1000 Precision tasks

11 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]

12 Intensity flux emitted "in a certain direction" φ Ω Images by MIT OCW.

13 Intensity flux emitted within a certain solid angle d A = Ω. d 2 A Ω = d 2 A Ω Images by MIT OCW.

14 Intensity flux emitted within a certain solid angle I in [W/sr] vs. [lm/sr] or Candela [Cd] 1 Candela = intensity of one candle

15 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.

16 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 o 330 o o Image by MIT OCW.

17 105 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 o 40 h = 10 ft d o 15 o 30o 45 o 60 o 75 o 180 cd Image by MIT OCW.

18 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.

19 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

20 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

21 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

22 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 Minimal luminance perceived: 10-5

23 Luminance measurement Eye = luminance-meter

24 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 pp. 3-1 to pp. 3-9 to pp. 4-1 to 4-6