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
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
25' L
2' )25(
25' L
2
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
Data for fluorescent lamps
Lumen output fall during the life time
Ref: Tao and Janis (2001)
Types:
• Incandescent
• Electric discharge • Fluorescent • HID High-intensity Discharge Lamp
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)
• 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
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
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 LightingType Color Temp.
(K)Efficacy
(lumens/W)CRI Lifetime
(1000 hours)
Mercury 5710 20-60 15-50 24
HPSHigh pressure
sodium
2100 140 22-70 16-40
LPSLow 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
LEDlight emitting diodes
~1 10+ years
Tritiumnuclear
0 10 – 20 years
Lamps are not the only thing
• Fixtures (luminaire)
• Application requirements
• Mounting
• Distribution
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