Objectives Describe the lighting parameters Learn about lamps Define project 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/ft2] directional emission of visible light

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 φ=45°. What is the illuminance level (E) at the center of the painting?

Solution Distance: Illuminance orthogonal to the beam E=I/L2=5000/ Ebeam= 100 fc Illuminance orthogonal to the painting Epainting= Ebeam/ Epainting=71 fc

Color of light Color temperature is used to express the color of the light

Surface color rendering Depending on the light type the surface colors can be different Depends on spectral energy distribution

Color rendering lamp source can cause a color shift

Color rendering index (CRI) Indicate if a lamp source will cause a color shift. Definition: CRI =100 for incandescing lamp with color temperature 3000K

Luminous efficacy Define the light output per unit of electric power input Efficacy = Lumens/Watt

Lifetime of lamps Rated life of lamp is time elapsed when 50% of group of lamp remain burning.

Lumen deprecation Lumen output fall during the life time Data for fluorescent lamps

Types: Incandescent Electric discharge Fluorescent HID High-intensity Discharge Lamp Ref: Tao and Janis (2001)

Incandescent Thomas Edison first incandescent lamp Efficacy of 1.4 lumens/watt Life – 750 to 1000 hours 10 – 20 % decay in output

Specialty Incandescent Lamps Halogen Low voltage Long-life Infrared Interference filters

Is Dimming Bad For Incandescent Lamps? - 10% lower Voltage - 25% lower light - life of lam doubles

Fluorescent Lamps Electrodes arc through mercury vapor Phosphors fluoresce in visible range Efficacy of 60 to 100 lumens/watt (after burn-in)

Ref: Tao and Janis (2001)

Fluorescent Lamps 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

Ballasts Why do we need ballasts? Types: 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

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 1/40th of the energy charges, lower demand, less maintenance, lower cooling bills More even illumination

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)

Ref: Tao and Janis (2001)

Types of HID Lighting Type Color Temp. (K) Efficacy (lumens/W) CRI Lifetime (1000 hours) Mercury 5710 20-60 15-50 24 HPS High pressure sodium 2100 140 22-70 16-40 LPS Low pressure sodium 1740 (yellow) 200 ~0 10-201 Metal Halide 3600 ~100 <70 10-20 1minimal decline in output with aging

Issues with HID lighting Long start-up ~ minutes Arc needs to stabilize, heat vapor Even longer restart Up to 40,000 hour life time

What is next in lamp technology LEDs - light emitting diodes Semiconductor technology Exit signs Electrodeless Lamps Induction lighting Microwave lighting High efficiency Possible interference with wireless networks Nuclear Light Source

Comparison Type Power (W) Lifetime Incandescent 40 2 – 8 months Fluorescent 10 – 25 1 – 2 years LED light emitting diodes ~1 10+ years Tritium nuclear 10 – 20 years

Lamps are not the only thing Fixtures (luminaire) Application requirements Mounting Distribution