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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 –

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Presentation on theme: "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 –"— Presentation transcript:

1 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

2 This class is more important than simply the material we cover! If you dont recognise the need to make a positive difference to our world, then we have failed you!

3 Summary of Lec. 2 Class answers re: 3 rd & 4 th optical sensor in mammalian eyes from Lec.2? Discuss in T2 Class answers to Batwing Question from Lec. 2? Demo Lux meter

4 Fundamentals of Light Part 2 Dr. Dave Irvine-Halliday ENEL 581

5 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

6 Illuminance Standards CIE – Commission Internationale de lÉclariage IESNA – Illumination Engineering Society of North America Type of ActivityIlluminance (Lux) Orientation and simple visual tasks (Public spaces) Common visual tasks (Commercial, Industrial and Residential) Special visual tasks (very small or very low-contrast critical elements) Sun (at sea level) 10 5 – 10 4 Lux Moon (at sea level) 0.1 Lux

7 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 5×105 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 afterimagessunlightafterimages A candle (6 lumen emitting into a hemisphere) can be seen at a distance of 10 miles (16 kms) in a clear atmosphere

8 Can 1 Watt WLED Lamps meet the Illumination Standards for reading? 27 cm above reading surface with 65° reflector

9 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 = cm Area meeting the NA Illumination Standards for reading (300 Lux). Ideal characteristic for a reading / task lamp – by developed world standards

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

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

12 Standards for the Developing World? Measurement of Illuminance Levels in Class

13 Same beam angle as single WLED, but higher illumination levels… IESNA CIE Winter 2005 class (acceptable level)

14 Colorimetry Science of Measuring Colors As it was inconvenient to have negative values in the matching functions CIE proposed a linear transformation of matching functions resulting in CIE x, y and z matching functions

15 CIE 1931 Color Matching Functions Where the weights, X, Y and Z define a color in the CIE XYZ space and C( ) = Color

16 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.

17 CIE 1931 Chromaticity Diagram 5 mm WLED X = 0.41 Y = 0.39

18 Mixing of Colors The Blue Experience

19 CIE 1976 Chromaticity Diagram 5 mm WLED X = 0.41 Y = 0.39

20 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

21 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)

22 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.

23 Table 1: CCT comparison for some light sources Correlated Color Temperature (CCT) Light SourceCCT °K Candle / Kerosene lamp~ W Incandescent2675 Compact Fluorescent4200 WLEDs5000 Daylight (noon)5400

24 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)

25 Table 2: CRI Comparison between some light sources Color Rendering Index (CRI) Light SourceCRI Candle / Kerosene lamp W Incandescent100 ?? Warm white Fluorescent55 Cool white Fluorescent65 Daylight Fluorescent73 WLEDs85

26 Color Rendering Index Analysis General Color Rendering Index R a (CRI) Integrates the reflectivity data for 8 specified samples Special color rendering indices, refer to six additional test samples Ra varies to up to 100, it might be negative.

27 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 (Φ v ) / Radiant Power (Φ e ) Radiant Efficiency (η e ): Dimensionless designates the ability of the light source to convert the consumed power into radiant flux Φ e (Can go from zero to unity). η e = Φ e / 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 Φ v (Characterizes the source) η v = Φ v / Power (P)

28 Luminous Efficiency Comparison Table 1: η v comparison for some light sources Light Source(lm/W) Candle / Kerosene lamp0.1 – 1 Incandescent Compact Fluorescent Tube Fluorescent WLEDs

29 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).

30 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.

31 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

32 References Lighting Principles: Mechanical and Electrical Equipment for buildings Stein, Benjamin. New York Wiley c2000, 9th Edition Chapter 18 Introduction to Solid State Lighting Arturas Zukauskas Wiley Interscience, 2002 Chapter 2 – Vision, Photometry and Colorymetry Lighting The Way, a key to independence Mariana Gross Figueiro Lighting Research Center

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