Key objectives in Lighting design

Visual performance

Physiological conditions

Visual qualityno 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

[-]

Image by MIT OCW.

Radio- and photometric quantities

Radiometry vs. Photometryabsolute (energy)

vs. V(λ)-dependent (light)

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)

Rel

ativ

e ef

ficie

ncy

[-]

Image by MIT OCW.

Radio- and photometric quantities

Four major quantitiesfluxilluminanceintensityluminance

Image by MIT OCW.

Radio- and photometric quantities

Fluxenergy / unit of time

φ in Watts [W] vs. lumen [lm]

Image by MIT OCW.

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 !

Images 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

Images 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

Image 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

Images 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

Images 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 = = = = = = =

Images 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 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

E = I cos(θ) / d2

θd

Image 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]inverse square law for point sourceintensity distribution

400

300

200

100

330o

300o

270o

240o 120o

90o

60o

30o

Image by MIT OCW.

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 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

180 cd

Image 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

Images 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

Image 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

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