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