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Objectives • Describe the lighting parameters • Learn about lamps • Define project 2

Objectives Describe the lighting parameters Learn about lamps Define project 2

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Objectives Describe the lighting parameters Learn about lamps Define project 2 Slide 2 Photometrics Luminous intensity [candela, cd] Define the ability of light source to generate light (illumination) in given direction Power luminous flux [lumen, lm] Quantity of light Illuminance light power density [foot-candela, fc] [lux, lx] SI units Density of light (illumination) incident on a surface Luminance - surface brightness [foot-lambert, lm/ft 2 ] directional emission of visible light Slide 3 Illuminance (E) depends on angle Example: Spot light with luminous intensity I= 5000cd is aimed at painting at the wall 5 ft from the light and the angle =45. What is the illuminance level (E) at the center of the painting? Slide 4 Solution Distance: Illuminance orthogonal to the beam E=I/L 2 =5000/ E beam = 100 fc Illuminance orthogonal to the painting E painting = E beam / E painting =71 fc Slide 5 Color of light Color temperature is used to express the color of the light Slide 6 Surface color rendering Depending on the light type the surface colors can be different Depends on spectral energy distribution Slide 7 Color rendering lamp source can cause a color shift Slide 8 Color rendering index (CRI) Indicate if a lamp source will cause a color shift. Definition: CRI =100 for incandescing lamp with color temperature 3000K Slide 9 Luminous efficacy Define the light output per unit of electric power input Efficacy = Lumens/Watt Slide 10 Lifetime of lamps Rated life of lamp is time elapsed when 50% of group of lamp remain burning. Slide 11 Lumen deprecation Data for fluorescent lamps Lumen output fall during the life time Slide 12 Ref: Tao and Janis (2001) Types: Incandescent Electric discharge Fluorescent HID High-intensity Discharge Lamp Slide 13 Incandescent Thomas Edison first incandescent lamp Efficacy of 1.4 lumens/watt Life 750 to 1000 hours 10 20 % decay in output Slide 14 Specialty Incandescent Lamps Halogen Low voltage Long-life Infrared Interference filters Slide 15 Is Dimming Bad For Incandescent Lamps? - 10% lower Voltage - 25% lower light - life of lam doubles Slide 16 Fluorescent Lamps Electrodes arc through mercury vapor Phosphors fluoresce in visible range Efficacy of 60 to 100 lumens/watt (after burn-in) Slide 17 Ref: Tao and Janis (2001) Slide 18 20,000 hour life for tubes Output falls off significantly (lumen deprecation) We define mean lumens at 40% expected life Environmental hazard because of mercury Significant improvement with lumen deprecation and life with new types of fluorescent lamps Start of the lamp vary with type of fluorescent lamp Fluorescent Lamps Slide 19 Ballasts Why do we need ballasts? Transformer higher voltage Limit the maximum flow of current - choke Types: Magnetic Noisier, cheaper, less efficient (more heat) Electronic Quieter, better power factor, more expensive Lower harmonic distortion Higher frequency Slide 20 Comparison Incandescent: 40 W 8760 hr/year = 350 kWh Demand charges, maintenance, additional cooling Uneven illumination LED: 1 W 8760 hr/year = 8.8 kWh 1/40 th of the energy charges, lower demand, less maintenance, lower cooling bills More even illumination Slide 21 High Intensity Discharge (HID) Arc through conducting vapor High temperature and pressure Ceramic or quartz tubes Glass protective casing Also need ballast (electric discharge lamps) Slide 22 Ref: Tao and Janis (2001) Slide 23 Types of HID Lighting TypeColor Temp. (K) Efficacy (lumens/W) CRILifetime (1000 hours) Mercury571020-6015-5024 HPS High pressure sodium 210014022-7016-40 LPS Low pressure sodium 1740 (yellow) 200~010-20 1 Metal Halide 3600~100