Transcript 346N_No22_Lighting_design_param

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:
L  5'  2
L  5'  2
• Illuminance orthogonal
to the beam
E=I/L2=5000/(5'  2 ) 2
Ebeam= 100 fc
• Illuminance orthogonal
to the painting
Epainting= Ebeam/ 2
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
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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?
• 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. Efficacy
CRI
Lifetime
(K)
(lumens/W)
(1000 hours)
Mercury
5710
20-60
15-50
24
HPS
2100
140
22-70
16-40
LPS
1740
200
~0
10-201
Low pressure
sodium
(yellow)
Metal
Halide
3600
~100
<70
10-20
High pressure
sodium
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
~1
10+ years
0
10 – 20 years
light emitting diodes
Tritium
nuclear
Lamps are not the only thing
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Fixtures (luminaire)
Application requirements
Mounting
Distribution