dspace@mit home - key objectives in lighting...
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Key objectives in lighting design
Qualificationsno strong "contrasts"good "color rendering"adequate "light levels"no "disturbing reflections"no direct "glare"
Radio- and photometric quantities
Radiometry vs. Photometryabsolute (energy)
vs. V(λ)-dependent (light)
350 400 450 500 550 600 650 700 750 800
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Wavelength [nm]
Rel
ativ
e Ef
ficie
ncy
[-]
Figure by MIT OCW.
Radio- and photometric quantities
Four major quantitiesfluxilluminanceintensityluminance
Figure by MIT OCW.
Radio- and photometric quantities
Fluxenergy / unit of time
φ in Watts [W] vs. lumen [lm]
Radio- and photometric quantities
Fluxenergy / unit of time
φ in Watts [W] vs. lumen [lm]
683 lumen/Watt at 555 nm : φlum [lm] = 683 •Σ V(λ) •φe [W]
75 watts
1055 lumens
70 watts
5600 lumens
Incandescence Discharge
verydifferent
efficacies !
Figures by MIT OCW.
Emission spectra
400 500 600 700
1.0
2.0
3.0
nm
400 500 600 700
1.0
2.0
3.0
nm 300 400 500 600
1.0
2.0
3.0
nm
250 300 350 400
1.0
2.0
3.0
nm
Rel
ativ
e En
ergy
Rel
ativ
e En
ergy
Continuous Discontinuous
Combined Rays
Figure by MIT OCW.
Radio- and photometric quantities
Flux
Illuminanceflux received / unit of surface E in [W/m2] vs. [lm/m2] or lux [lx]
∆φ
∆S
Figures by MIT OCW.
Radio- and photometric quantities
Flux
Illuminanceflux received / unit of surface E in [W/m2] vs. [lm/m2] or lux [lx]
Full moon Overcast sky Sunlight
0.01 Lux 8'000 - 20'000 Lux 100'000 Lux
Figure by MIT OCW.
Radio- and photometric quantities
Flux
Illuminanceflux received / unit of apparent surface (cosine ("Lambert") law)E in [W/m2] vs. [lm/m2] or lux [lx]
α∆φ∆SE⊥ =
E
= = =
α α = E= E= E⊥. . cos ααα
Figures by MIT OCW.
Radio- and photometric quantities
Flux
Illuminanceflux received / unit of apparent surface (cosine ("Lambert") law)E in [W/m2] vs. [lm/m2] 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
Radio- and photometric quantities
Flux
Illuminanceflux 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
Intensityflux emitted "in a certain direction"
∆Ω
∆φ
Figures by MIT OCW.
Radio- and photometric quantitiesFlux
Illuminance
Intensityflux emitted within a certain solid angle
d
∆Ω∆Ω
∆A
∆A = ∆Ω.d2
d2∆A
∆Ω = = = = = = =
Figures by MIT OCW.
Radio- and photometric quantities
Flux
Illuminance
Intensityflux emitted within a certain solid angleI in [W/sr] vs. [lm/sr] or Candela [Cd]
1 Candela = intensity of one candle
Radio- and photometric quantitiesFlux
Illuminance
Intensityflux emitted within a certain solid angleI in [W/sr] vs. [lm/sr] or Candela [Cd]inverse square law for point source
Figures by MIT OCW. ∆Ω
∆φ∆φ∆φ∆φd
∆AE =∆φ∆Α d2
∆φ∆Ω.d2= =
Ι
Radio- and photometric quantities
Flux
Illuminance
Intensityflux emitted within a certain solid angleI in [W/sr] vs. [lm/sr] or Candela [Cd]inverse square law for point source
Figure by MIT OCW.
E = I cos(θ) / d2
Radio- and photometric quantities
Flux
Illuminance
Intensityflux emitted within a certain solid angleI in [W/sr] vs. [lm/sr] or Candela [Cd]inverse square law for point sourceintensity distribution
400
300
200
100
330o
300o
270o
240o 120o
90o
60o
30o
Figure by MIT OCW.
Radio- and photometric quantitiesFluxIlluminanceIntensity
flux emitted within a certain solid angleI in [W/sr] vs. [lm/sr] or Candela [Cd]inverse square law for point sourceintensity distribution
h = 10 ft d
30°
200
180
160
140
120
10080
60
40
0o 15o30
o
45o
60o
75o
90o
105o
120o
135o
150o
165o180
o
Figure by MIT OCW.
Radio- and photometric quantities
Flux
Illuminance
Intensity
Luminanceflux emitted by apparent surface in a given direction≈ I/m2 (or M/sr)L in [Cd/m2]
∆I
∆Ω∆φ
∆Ss
Source Ns
θ
Figures by MIT OCW.
Radio- and photometric quantities
Flux
Illuminance
Intensity
Luminanceflux emitted by apparentsurface in a given direction≈ I/m2 (or M/sr)L in [Cd/m2]
S
L = I / (S . cos θ)L = I / Sa
Sa
θ
Radio- and photometric quantities
Flux
Illuminance
Intensity
Luminanceflux emitted by apparentsurface in a given direction≈ I/m2 (or M/sr)L in [Cd/m2] Intensity variation Luminance variation
lambertian surface lambertian surface
Specular
Diffuse/Specular Specular/Spread Diffuse/Spread
Spread Diffuse
Figures by MIT OCW.
Radio- and photometric quantities
Flux
Illuminance
Intensity
Luminanceflux emitted by apparentsurface in a given direction≈ I/m2 (or M/sr)L in [Cd/m2]
Primary sources• Sun• Incandescent lamp (100 W, bright)• Incandescent lamp (100 W, frosted)• Fluorescent tube (40 W, 38 mm)• Candle• Computer screen
Cd/m2
1 650 000 0006 000 000
125 0005000 - 8000
5000100-200
Radio- and photometric quantities
Flux
Illuminance
Intensity
Luminanceflux emitted by apparentsurface in a given direction≈ I/m2 (or M/sr)L in [Cd/m2]
Cd/m2
2 500 - 3000100
505
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: 10-5
Radio- and photometric quantities
Luminance measurementEye = luminance-meter
Radio- and photometric quantities
Luminance measurement
Integrating sphere
Radio- and photometric quantities
Reading relevant to lecture topics:"IESNA Lighting Handbook" (9th Ed.): pp. 2-1 to 2-3 + pp. 2-9 to 2-11