EET-314 LECTURE 1.pdf

EET-314 LIGHTING DESIGN AND TECHNOLOGY Lecture # 1 School of Engineering Technology & Applied Science (SETAS) LIGHT, VISION & COLOUR Objectives Definition of light Describe the physics of light –Light as waves –Light as parti...

EET-314 LIGHTING DESIGN AND TECHNOLOGY Lecture # 1 School of Engineering Technology & Applied Science (SETAS) LIGHT, VISION & COLOUR Objectives Definition of light Describe the physics of light –Light as waves –Light as particles Describe the concept of vision Describe colour and colour temperature SETAS - AMAT: EET-314 Lecture #1 2  Definition of Light: What is Light? Definition: Electromagnetic radiation or energy transmitted through space or a material medium in the form of electromagnetic waves (definition in physics) Light is defined as visually evaluated radiant energy – light is that part of the electromagnetic spectrum visible by the human eye (illuminating engineering definition). SETAS - AMAT: EET-314 Lecture #1 3 Definition of Light: What is Light? Light is known to exhibit the properties of both electromagnetic waves and discrete particles Wave-particle duality We will examine the two cases: Light as Electromagnetic Waves Light as quantized particles (photons) SETAS - AMAT: Course Code Lecture #1 4 Definition of Light: What is Light? As a wave… As a particle… A small disturbance in an Particles of light (photons) travel electric field creates a small through space. magnetic field, which in turn These photons have very creates a small electric field, specific energies that is, light is and so on… quantized. Light waves can interfere with Photons strike your eye (or other other light waves, canceling or sensors) like a very small bullet, amplifying them! and are detected. The color of light is determined by its wavelength. SETAS - AMAT: Course Code Lecture #1 5 Physics of Light: Electromagnetic Waves James Clerk Maxwell described light as electromagnetic radiation that consists of waves and travels from its source in all directions Unlike sound waves that consist of material particles, light consists of perpendicular electric and magnetic field waves SETAS - AMAT: EET-314 Lecture #1 6 Physics of Light: Electromagnetic Waves These waves are known as Transverse Waves Wavelength (λ) Equation: λ = v/f, where v is the velocity and f is the frequency of the wave Wavelengths of light are typically measured in nanometers (nm), or billionths of a meter SETAS - AMAT: EET-314 Lecture #1 7 Physics of Light: Electromagnetic Waves Interesting facts of EM waves: Can travel through vacuum, empty space and matter EM waves do not transfer energy through vibration but rather through electromagnetic radiation Speed of an EM wave is dependent upon the material through which it is traveling EM waves travel at the speed of light in a vacuum SETAS - AMAT: EET-314 Lecture #1 8 Physics of Light: Electromagnetic Spectrum Electromagnetic spectrum is a complete range of EM waves Visible light only represents a small band of the spectrum SETAS - AMAT: EET-314 Lecture #1 9 Physics of Light: Electromagnetic Spectrum White Light Violet 380-435 nm Blue 435-500 nm Green 500-565 nm Yellow 565-600 nm Orange 600-630 nm Red 630-780 nm White light emitted by the sun or an incandescent lamps is a mixture of all wavelengths in the visible spectrum White light can be separated into its components by means of a prism SETAS - AMAT: EET-314 Lecture #1 10 Physics of Light: Wave-Particle Duality, Photoelectric Effect Electrons are emitted when light shines on a material. This is known as the Photoelectric Effect. Electrons become dislodged when wave-like particles strike the surface. This phenomena led scientists like Max Plank and Albert Einstein to hypothesize that light exists as discrete wave packets. SETAS - AMAT: EET-314 Lecture #1 11  Physics of Light: Electromagnetic Quantum Theory In 1900, Max Plank assumed that energy of radiation is emitted in discrete indivisible portions called quanta For visible radiation (light) the term photons is used Courtesy of PVEducation.com http://www.pveducation.org/pvcdrom/properties-of-sunlight/properties-of-light Phillips: Theory of Light and Lighting http://www.pveducation.org/pvcdrom/properties-of-sunlight/properties-of-light SETAS - AMAT: EET-314 Lecture #1 12 Physics of Light: Electromagnetic Quantum Theory The energy content of a quantum of radiation is directly related to its frequency or wavelength: E = h * f or E = h * c / λ where: E = energy (Joules) f = frequency (Hz) h = Planck’s constant (6.626 x 10-34 J * sec) c = speed of light in a vacuum (2.998 x 108 m/sec) λ = wavelength (m) Equation shows that shorter the wavelength, the higher the energy of radiation (e.g. UV rays, X rays and gamma ray). SETAS - AMAT: EET-314 Lecture #1 13  Physics of Light: Electromagnetic Quantum Theory Example 1: A light particle has a frequency of 500 THz. Calculate the energy content of quantum radiation. Also calculate the wavelength. SETAS - AMAT: EET-314 Lecture #1 14 Physics of Light: Interaction of Light and Surfaces When light strikes a surface, it can either be transmitted, reflected, refracted or absorbed SETAS - AMAT: EET-314 Lecture #1 15  Physics of Light: Reflection On a smooth surface, the angle of incidence (θi) equals the angle of reflection (θr) When precise light control is required, high efficiency mirror reflectors are used Depending on shape of mirror and position of light source different beam patterns can be produced Phillips: Theory of Light and Lighting http://www.pveducation.org/pvcdrom/properties-of-sunlight/properties-of-light SETAS - AMAT: EET-314 Lecture #1 16 Physics of Light: Transmission and Absorption Light falling on a surface that is not reflected is either absorbed or transmitted Absorption For non-transparent surfaces, light that ‘disappears’ in the surface and is converted to heat energy Percentage of absorption depends on the angle of light beam and wavelength (eg. Red surface reflects red light but absorbs most other colours) Transmission Transparent material will allow part of the light to pass through it (eg. Glass, clear water etc.) Transmission is wavelength dependant SETAS - AMAT: EET-314 Lecture #1 17 Physics of Light: Refraction Refraction is the bending of a light ray as is passes from one medium into another of different density Created by the change in the speed of light from one medium to another Index of refraction (n) is the ratio of the speed of light in a vacuum (c) and the speed of light in a medium (v) n = c/v Material n Vacuum 1.000 Different material have different Air 1.000277 index of refraction Water 4/3 Crown glass 1.50-1.62 Diamond 2.417 SETAS - AMAT: EET-314 Lecture #1 18 Physics of Light: Refraction Snell’s Law relates indices of refraction of two media to the direction of propagation n1 sinθ1 = n2 sinθ2 capuphysics.ca Example 2: A ray of light is incident on an air-to-glass boundary at an angle of 30°with the normal. If the index of refraction of the glass is 1.65, what is the angle of the refracted ray with respect to the normal? SETAS - AMAT: EET-314 Lecture #1 19  Vision Vision is one of the most important sensory systems for humans Vision is our primary means of interacting with and learning about our world Our eyes and brain are the primary organs of our visual system Our ability to see is dependent on light and properties of objects SETAS - AMAT: EET-314 Lecture #1 20 Vision: Cross section of human eye http://futurehumanevolution.com/visualizing-the-universe-human-vision SETAS - AMAT: EET-314 Lecture #1 21 Vision: Human retina https://www.fastbleep.com/biology-notes/20/716 SETAS - AMAT: EET-314 Lecture #1 22 Vision: Rods and Cones Cones Rods Photopic “Day” Vision Scotopic “Night” Vision Color Vision Black & White Vision High Light Levels Low Light Levels High Acuity Low Acuity Sensitive to Brightness Sensitive to Motion Central Vision Peripheral vision SETAS - AMAT: EET-314 Lecture #1 23  Vision: Photopic, Mesopic and Scotopic Vision http://noribachi.com/wp-content/uploads/2013/09/VISIONS.png SETAS - AMAT: EET-314 Lecture #1 24 Vision: Photopic, Mesopic and Scotopic Vision Peak luminous efficiency occurs between 507-555 nm SETAS - AMAT: EET-314 Lecture #1 25 Vision : Adaption Light Adaption – Dark to light – Uncomfortable transition – Takes only a few seconds Dark Adaption – Light to dark – Not typically uncomfortable – Can take up to 20 minutes for full adaption SETAS - AMAT: EET-314 Lecture #1 26  Vision: Visibility Factors Some of the common visibility factors are: Task Size Luminance (Brightness) Speed/Time Contrast Glare Age Colour SETAS - AMAT: EET-314 Lecture #1 27  Vision: Task Size Task size is related to the viewing distance Example: Fine print of document vs. roadside billboard SETAS - AMAT: EET-314 Lecture #1 28 Vision: Luminance Luminance or brightness is how much light is directly reflected or transmitted from a surface SETAS - AMAT: EET-314 Lecture #1 29 Vision: Contrast Visibility my be reduced with Visibility my be reduced with lower reflectance of the lower reflectance of the background. background. Tasks of high contrast Tasks of high contrast generally require less light generally require less light SETAS - AMAT: EET-314 Lecture #1 30  Vision: Glare There are two main types of glare: Direct ▪ Bright light directly in employee’s field of view Reflected (or indirect) ▪ Caused by light bouncing off nearby surfaces into the worker’s eyes (Adapted from: Computer Ergonomics: Workstation Layout and Lighting, 2004, p.10.) SETAS - AMAT: EET-314 Lecture #12 31  Vision: Speed/Time How long do you have to view an object? Moving objects affect visibility Visibility changes with time of day SETAS - AMAT: EET-314 Lecture #1 32  Vision: Age A 60 year old needs 3 times more light than a 20 year old! http://www.everyeye.org.uk/htms/oldAgeVision.htm SETAS - AMAT: EET-314 Lecture #1 33  Colour: Primary Colours White light is composed of a mixture of colours: Primary colours: –Red, Green and Blue Secondary colours: –Cyan, Magenta and Yellow SETAS - AMAT: EET-314 Lecture #1 34  Colour: Additive Colour Mixing - Light Additive colour mixing refers to the mixing of light Yellow, magenta and cyan consist of a mix of two primary colours Complementary Colours: Yellow, magenta and cyan Red, Green, Blue = White Colour mixing Additive mixing of a complementary colour with appropriate primary gives white SETAS - AMAT: EET-314 Lecture #1 35  Colour: Subtractive Colour Mixing - Pigments Subtractive colour mixing refers to the mixing of pigments Primary Mixing: If coloured paints mix, the result is always darker than original paints Cyan, Magenta, Yellow = Black Subtractive mixing of the complementary colours will Complementary produce the primary colours Mixing: SETAS - AMAT: EET-314 Lecture #1 36 Colour: Spectral Power Distribution SETAS - AMAT: EET-314 Lecture #1 37  Colour: Spectral Power Distribution The human eye is most sensitive to the green-yellow wavelengths SETAS - AMAT: EET-314 Lecture #1 38  Colour: CIE Chromaticity Chart Any colour can be made using red (R), green (G) and blue (B) primary radiations One unit of colour can be matched by r proportion of (R), g proportion of (G) and b proportion of (B) such that: r + g + b = 1.0 CIE chromaticity chart specifies R, G, and B primaries as X, Y and Z and are plotted in terms of x and y. x + y + z = 1.0 Note: it is only necessary to specify two of the three to identify the colour SETAS - AMAT: EET-314 Lecture #1 39 © 2014 Robert Bean. Courtesy Routledge Publishing Colour: Correlated Colour Temperature (CCT) Method for specifying colours related to the temperature of a ideal black-body radiator Black body is an “idealized” solid body that absorbs all electromagnetic radiation If a solid body is heated colour will change ranging from dull red to bluish white Colour temperature over 5000 K are cool colours (bluish-white), with colours 2700-3000 K are called warm (yellowish white through red) Thermal radiators like the sun and incandescent bulbs approximate a black-body radiator LED and fluorescent light sources do not resemble a black body radiator (light emitted does not represent its temperature), they are assigned a Correlated Colour Temperature SETAS - AMAT: EET-314 Lecture #1 40 Colour Temperature CIE Diagram showing CCT Values Use locus points of full radiator (black body) to specify colour in terms of R,G, & B © 2014 Robert Bean. Courtesy Routledge Publishing SETAS - AMAT: EET-314 Lecture #1 41  Colour Temperature: Correlated Colour Temperature (CCT) Temperature Source Match flame, low pressure 1,700 K sodium lamps (LPS/SOX) 1,850 K Candle flame, sunset/sunrise 2,400 K Standard Incandescent lamps 2,550 K Soft White Incandescent lamps "Soft White" compact fluorescent 2,700 K and LED lamps Warm White compact fluorescent 3,000 K and LED lamps 3,200 K Studio lamps, photofloods, etc. 3,350 K Studio "CP" light 4,100–4,150 K Moonlight 5,000 K Horizon daylight Tubular fluorescent lamps orcool 5,000 K white/daylight compact fluorescent lamps (CFL) 5,500–6,000 K Vertical daylight, electronic flash 6,200 K Xenon short-arc lamp 6,500 K Daylight, overcast 6,500–9,500 K LCD or CRT screen 15,000–27,000 K Clear blue poleward sky These temperatures are merely characteristic; considerable variation may be present. https://en.wikipedia.org/wiki/Color_temperature SETAS - AMAT: EET-314 Lecture #1 42 Colour Temperature: Correlated Colour Temperature (CCT) Example 3: Of the colour temperatures marked on the CIE diagram, to which one do the co-ordinates x = 0.3133 and y = 0.3235 relate? What is the z value? SETAS - AMAT: EET-314 Lecture #1 43  Colour: Colour Rendering Index (CRI) Another property of lamps that is related to how we see different colors under its light. The CRI is a number between 0 and 100. ▪ The reference standard is a very special incandescent lamp at a lighting laboratory. ▪ The light output of this lamp sets the standard for CRI as 100. Users can find data on the CRI of lamps in catalog or product specifications 44 Colour: Colour Rendering Index (CRI) The CRI is generally associated with the quality of lighting. The U.S. EPA Green Lights program rates CRI and lighting quality as follows: 75 – 100 Excellent 65 – 75 Good 55 – 65 Fair 0 – 55 Poor CRI and the color temperature of a particular lamp determine how we see colors under that lamp. 45 Colour: Colour Rendering Index (CRI) Black and White (CRI: 0) Full Colour (CRI: 100) 46  Summary 1. Light can be described as both electromagnetic waves and as discrete wavelike particles (photons) 2. Visible light only represents a very narrow ban of the electromagnetic spectrum 3. White light is composed of all colours in the visible light spectrum 4. For refracted light rays, direction of propagation can be determined using Snell’s Law 5. Light hitting a surface can be either: reflected,refracted transmitted or absorbed 47  Summary 6. Cones are used for day vision (photopic) and rods are for night vision (scotopic) 7. Visibility factors affect vision 8. Secondary colours can be created from primary colours (Red, Green and Blue) 9. There are two methods for specifying light colour: CIE chromaticity chart (x,y,z) and Correlated Colour Temperature (CCT) 10. Human vision is most sensitive to yellow-green wavelengths. 11. The Color Rendering Index (CRI) indicates how accurate a light source is at rendering color 48