“Success is not the key to happiness. Happiness is the key to success.

If you love what you are doing, you will be successful.”

Albert Schweitzer 1875 – 1965

This class is more important than simply the material we cover!

If you don’t recognise the need to make a positive difference to our world, then we have failed you!

Summary of Lec. 2

Class answers re: 3rd & 4th optical sensor in mammalian eyes from Lec.2?

Discuss in T2Class answers to Batwing Question from Lec. 2?Demo Lux meter

Fundamentals of Light Part 2

Dr. Dave Irvine-Halliday

ENEL 581

Outline

I. Illumination Standards (CIE, IESNA)

II. Colorimetry – CCT, CRI

III. Psychology of color

IV. Physiology – Young eyes, old eyes

V. Lumen Efficacy and Efficiency

VI. Lighting Sources Comparison

Illuminance Standards

CIE – Commission Internationale de l’Éclariage IESNA – Illumination Engineering Society of North America

Type of Activity Illuminance (Lux)

Orientation and simple visual tasks (Public spaces)

30 - 100

Common visual tasks (Commercial, Industrial and Residential)

300 - 1000

Special visual tasks (very small or very low-contrast critical elements)

3000 - 10000

Sun (at sea level) 105 – 104 Lux Moon (at sea level) 0.1 Lux

The human eye is capable of seeing somewhat more than a 2 trillion-fold range: The presence of white objects is somewhat discernible under starlight, at 5×10−5 lux, while at the bright end, it is possible to read large text at 10+8 lux, or about 1,000 times that of direct sunlight, although this can be very uncomfortable and cause long-lasting afterimages

A candle (6 lumen emitting into a hemisphere) can be seen at a distance of 10 miles (16 kms) in a clear atmosphere

Can 1 Watt WLED Lamps meet the Illumination Standards for reading?

Lamp height vs illuminance level over the lit up surface, using Mark 2 lamp.

Aug 12, 2003

0

0.1

0.2

0.3

0.4

0.5

0.6

0 100 200 300 400 500 600

Illuminance Level (lux)

He

igh

t fr

om

lit

up

su

rfa

ce

(m

ts)

No Optics

65° AlluminumReflector

50° Metalized Plastic

Fresnell lens

Reflector and FresnellLens

27 cm above reading surface with 65° reflector

Illumination levels offered by 1 Watt WLED Lamps

McTavish

WLED Task Lamp

Tan 32.5° = (d/2) / 0.27m

d/2 = 0.27m tan 32.5°

d = 34.40 cm

d = 34.40 cm

Area meeting the NA Illumination Standards for reading (300 Lux).

“ Ideal characteristic fora reading / task lamp – by developed world standards ”

Nichia's 5mm WLED Light Beam PatternManufacturer's Code: NSPW500BS

Light meter placed 50 cms away from sourceOct 28, 2004

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Light beam's angle of distribution (Degrees)

Lu

min

ou

s P

ow

er

De

ns

ity

(L

ux

)

Sample 1

Sample 2

Sample 3

What happens if we use more than one WLED in a lamp?

15 x 5mm Nichia's WLED Array Light Beam PatternManufacturer's Code: NSPW500BS

Light meter placed 50 cms away from sourceOct 28, 2004

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Light beam's angle of distribution (Degrees)

Lu

min

ou

s P

ow

er

De

ns

ity

(L

ux

)

“Same beam angle as single WLED, but higher illumination levels…”

Standards for the Developing World?

“Measurement of Illuminance Levels in Class”

15 x 5mm Nichia's WLED Array Light Beam PatternManufacturer's Code: NSPW500BS

Light meter placed 50 cms away from sourceOct 28, 2004

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Light beam's angle of distribution (Degrees)

Lu

min

ou

s P

ow

er

De

ns

ity

(L

ux

)

“Same beam angle as single WLED, but higher illumination levels…”

IESNA

CIE

Winter 2005 class(acceptable level)

CIE 1931 Color Matching Functions

Where the weights, X, Y and Z define a color in the CIE XYZ space and C() = Color

CIE 1931 Chromaticity Diagram

As the z component bears no additional information, it is often omitted. xy space is just a projection of the 3D XYZ space Each point in xy corresponds to many points in the original space.

CIE 1931 Chromaticity Diagram

5 mm WLED X = 0.41 Y = 0.39

CIE 1976 Chromaticity Diagram

5 mm WLED X = 0.41 Y = 0.39

Correlated Color Temperature (CCT)

CCT is defined as the absolute temperature (expressed in degrees Kelvin) of a theoretical black body whose chromaticity most nearly resembles that of its light source.

CCT rating is an indication of how "warm" or "cool" the light source is.

Ambient color and CCT of light have a psychological effect over the users.

Cooler light

Warmer light

Planckian Locus(Black body radiator)

A - tungsten (2856° K)B - direct sunlight (4870° K) C - overcast sunlight (6770° K)D - daylight (6504° K)E - Equal energy

Correlated Color Temperature (CCT)

Psychology of Color

Environmental Color affects mood and feeling and is a common experience. From studies (Wohlfarth, Faber, Akashi, 1986) it has also been proved that light has also physiological effects on humans.

Red and Red hues of CCT, creates a sensation of heat. Tend to increase body tension, and stimulates the autonomic nervous system.

Blue and blue hues of CCT, creates a sensation of cool, Release tension and have lesser physiological effects.

Table 1: CCT comparison for some light sources

Correlated Color Temperature (CCT)

Light Source CCT °K

Candle / Kerosene lamp ~ 1800

100 W Incandescent 2675

Compact Fluorescent 4200

WLEDs 5000

Daylight (noon) 5400

Daylight, by definition has a color rendering index of 100.

The higher the color rendering index from a lamp the better it is.

CRI ≥ 90 Excellent CRI ≥ 85 Very Good

60 ≥ CRI ≥ 80 Some Color Distortion

CRI is defined as the capacity of artificial light sources to render the colors of the illuminated objects as compared to daylight at the same color temperature. CRI ≤ 60 Serious Color Distortion

Poor rendering indexes put strain on the eyes because of having to correct the color of objects.

Color Rendering Index (CRI)

Table 2: CRI Comparison between some light sources

Color Rendering Index (CRI)

Light Source CRI

Candle / Kerosene lamp 80

100 W Incandescent 100 ??

Warm white Fluorescent 55

Cool white Fluorescent 65

Daylight Fluorescent 73

WLEDs 85

Luminous Efficacy and Efficiency

Luminous Efficacy (K): The ability of the radiated energy to produce a visual sensation, which is measured in lumens per watt of emitted light (Characterizes the radiation spectra rather than the source).

K = luminous flux (Φv) / Radiant Power (Φe)

Radiant Efficiency (ηe): Dimensionless designates the ability of the light source to convert the consumed power into radiant flux Φe (Can go from zero to unity).

ηe = Φe / Power (P)

Luminous Efficiency: Measured in lumens per watt, it is the ability of the light source to convert consumed electrical power into visible luminous flux Φv (Characterizes the source)

ηv = Φv / Power (P)

Luminous Efficiency Comparison

Table 1: ηv comparison for some light sources

Light Source (lm/W)

Candle / Kerosene lamp 0.1 – 1

Incandescent 5 - 18

Compact Fluorescent 30 - 79

Tube Fluorescent 82 - 100

WLEDs 30 - 120

Luminous Efficiency Trends Comparison

(1) 5mm WLED introduced by Nichia Corporation of Japan in 1996, (2) Luxeon Star – the first high-flux WLED in the market developed by Lumileds, USA (3) Luxeon K2 – the brightest device up to date (also developed by Lumileds).

Physiology of Vision

Aging of the human eye “a natural process” :

involves loss of accommodation of focussing capability reduction of pupil size, thus reducing the amount of light entering the eye (older people require extra lighting). Thickening of the optical lens (absorbing more light and scattering it). Images with less contrast and sharpness.

20 Year old eyes can receive 6 times more light than a 80 years old ones in bright conditions and 16 times more light in dark conditions.

Good lighting can make the difference between seeing and not seeing for older adults.

Physiology of Vision

Recommendations:

Increase illumination levels over reading and working spaces (increase of luminous flux of light sources)

Diffuse light, keep a uniform light distribution

Avoid glare or direct view of light sources or reflections

Use high color rendering index light sources

References

Lighting Principles:

Mechanical and Electrical Equipment for buildingsStein, Benjamin. New York Wiley c2000, 9th EditionChapter 18

Introduction to Solid State Lighting

Arturas ZukauskasWiley Interscience, 2002Chapter 2 – Vision, Photometry and Colorymetry

Lighting The Way, a key to independence

Mariana Gross FigueiroLighting Research Center