2ECEN2060
US Residential & Commercial Energy Consumption
* DOE, EIA, Annual Energy Review, 2006
• Electricity accounts for ~ 50% of energy usage
• Low overall efficiency in generation, transmission and distribution (~30-40%) of electricity
• Improving efficiency of major electric loads is very important!
1 Energy losses during generation, transmission and distribution of electricity
3ECEN2060
DOE Initiatives & Programs
• Energy Star
� Voluntary labeling program, DOE and EPA, to encourage energy efficiency
� “in 2006, saved enough energy to avoid greenhouse gas emissions from 25 million cars – all while saving $14 billion” Energy Star website
� Change a light, change the world campaign
• Solid-state lighting program
• High Performance Buildings
� Working with all aspects of building design and occupancy
• Net Zero Energy Buildings and Homes (by 2025)
4ECEN2060
4 Times SquareDOE high performance building showcase
• $500 million office tower, Manhattan
• 10-15% lower operating costs, $500K annual energy savings, 5 year payback
• Lighting
� High performance light fixtures, fluorescent, HID, LED lighting, occupancy sensors, central controls for public areas, low-e glass curtain walls
• Heating & cooling
� Natural gas absorption chillers/heaters
� Variable speed drives on pumps & fans with occupancy sensors and central control
• Generation
� 15 kW PV installation and two 200 kW fuel cells
• Other
� indoor air quality, waste management, materials
5ECEN2060
US Office Building Total Energy Use
30% Lighting
25% Space Heating
16% Office Equipment
9% Water Heating
9% Space Cooling
11% Other
End Use Consumption (TBtu)
Lighting 294.19
Space Heating 254.98
Office Equipment 158.65
Space Cooling 95.38
Water Heating 90.66
Miscellaneous 54.83
Ventilation 54.10
Cooking 11.37
Refrigeration 4.50
• Lighting represents ~ 40% to 50% of electricity usage in office buildings
• Existing energy efficient lighting technologies can reduce electricity usage for
lighting by 20% to 50% in office buildings
• Reductions up to 90% in lighting energy consumption are possible in
residential, where inefficient lighting is dominant
• Lighting accounts for about 10% of energy usage in residential
6ECEN2060
Lighting Color Definitions
• Color Rendering Index (CRI)
� Measure of the ability of a source to reproduce the colors reflected off of test samples compared to a reference source (black body or daylight), 0 to 100
� Incandescent bulb: 100
• Correlated color temperature
� Measure of the color temperature of a black body radiator which in the perception of the human eye most closely matches the light from the lamp
� Candle: 1850K
� Incandescent bulb: 2800K – 3300K
� “warm white” lamp: 3000K
� “cool white” lamp: 4200K
CIE (International Commission on Illumination)x,y chromaticity space
7ECEN2060
Photopic Vision and CIE Standards
CIE standard observer color-matching functions
Normalized response spectra of human cones, Short, Middle, and Long
• Note that different sources generating a variety of combined wavelengths can be perceived as the same color
• When such sources reflect light off of objects, the observed color of the objects may not be the same (depending on which wavelengths the objects absorb)
8ECEN2060
Lighting Energy Definitions
• Background
� Radiant energy, Q [J]: Energy traveling in the form of electromagnetic waves, in joules
� Radiant flux, [W]: time rate of flow of radiant energy, in watts.
• Luminous flux, [lm]
� Total time rate of flow of radiant energy, evaluated by standardized CIE visual response, in lumens
� 60 W incandescent bulb: 850 lm
� 100 W incandescent bulb: 1700 lm
• Luminous efficacy, [lm/W]
� Total luminous flux emitted by a lamp divided by the total lamp power input, lumens per watt
� Candle: 0.3 lm/W
� 60 W incandescent bulb: 14 lm/W
� Max possible: 683 lm/W (corresponding to 100% efficiency, 555 nm green)
10ECEN2060
Incandescent Light Sources
• Operation� Generates light by incandescence: release of
electromagnetic radiation in visible range due to surface temperature
� Thin tungsten filament heated with electric current� Low pressure inert gas and protective enclosure to
prevent oxidation and reduce evaporation� Operates directly from the AC line: suitable for AC
or DC operation; custom filament manufacturing for product designs over the widest range of voltages and power levels of any light source
� Life decreases rapidly with temperature• Halogen improves life at high temperature
• Performance� CRI: 100; CCT: ~3000K� Lifetime: 1000 hours� Efficacy / efficiency:
• 40 W tungsten: 12.6 lm/W, 1.9%• 100 W tungsten: 17.5 lm/W, 2.6%• Quartz halogen: 24 lm/W, 3.5%• Theoretical limit: at 6600 K (11500 °F), 95 lm/W
� Cost: $0.2/klm - $0.5/klm
Line voltage double
spiral filament
11ECEN2060
• Operation� Electrical discharge through an ionized gas (plasma) in a glass, quartz or ceramic
tube using electric current or electromagnetic fields� Noble gas mixture, together with mercury, sodium, and/or metal halides material� Accelerated free electrons collide with gas and metal atoms, get excited to a
higher state, then fall and emit a photon in visible or ultraviolet (UV) spectrums� UV lamps use phosphor coatings to down-convert to visible
• Technologies� Fluorescent lighting (LFL, CFL, CCFL, EFL)
• home, office, LCD backlighting
� High intensity discharge (HID)• very efficient area lighting and automotive
� Specialty• Neon, tanning lamps, flash and strobes
• Performance� CRI: 5 to 85� CCT: 3000K to 7000K� Lifetime: 10,000 – 20,000 hours� Efficacy: 30 lm/W to 150 lm/W� Cost: $0.4/klm - $3.0/klm
Discharge Lamp Technologies
LFL CFL EFL HIDCCFL
1-5 mg of mercury per bulb
12ECEN2060
Challenges in Discharge Lamps
High intensity discharge (HID) lamp
ignition example
Lamp Voltage
Lamp Current
Tglow = 4 s
• Ignition� Require very high voltage to ignite
the lamp: 100s V to 30 kV� During ignition and glow-to-arc, lamp
may alternately behave in open and shirt circuit, rectifying and resistive modes
• Stability� Lamp is unstable when driven from a
voltage source• Resistance decreases with increases
in current
� DC drive results in asymmetrical degradation of electrodes and other detrimental effects
� Internal acoustic resonances can cause dramatic failures
• Electrode sensitivity� Electrodes require optimal heating for
maximum life� Difficult to control at ignition and with
dimming (variable power)
13ECEN2060
Discharge Lamp Ballasts
• Requirements
� High-voltage ignition strike to ionize the gas
• Ignition current must be limited to protect the lamp
• Electrode heating reduces ignition voltage
� AC drive• Avoid migration of material to one end of the lamp
• Even wear of the electrodes
� Current source
• Lamp has negative resistance characteristic
� (Optional) dimming control
• Ballast types
� Magnetic
� ElectronicCFL with electronic ballast
14ECEN2060
Environmental concerns
• Up to 5 mg of mercury per lamp
• Lifetime limited by electrolytic capacitor in electronic ballasts
• Disposal and handling of waste issues
A comparison favorable to CFL. This is a controversial topic
15ECEN2060
Solid State Lighting Technologies
• Operation� Semiconductor diode pn junction that emits
photons when forward biased � High brightness, HB-LEDs
• Operate at currents from 100 mA to 10 A• Voltages from 2 V to 4 V• 4 to 20 LEDs: 60 W equivalent
� White LEDs• Visible RGB• Blue+phosphor• UV+phosphor
• Applications� Area lighting, LCD backlighting, flashlights,
automotive, specialty lighting, toys, medical
• Performance� CRI: 80 to 95
• Discussions on new measures for color performance
� CCT:� Lifetime: 50,000 hours
• Best estimate by models and accelerated testing
� Efficacy• Commercial: 20 lm/W to 60 lm/W• Research labs: 120 lm/W to 200 lm/W• Good Fixture efficiency is a major concern
� Cost: $50/klm to $150/klm• Expected to drop rapidly
18ECEN2060
Color Shift: Current and Temperature Effects
The spectrum of LEDs shifts
towards longer wavelength
with increasing temperature
(Red Shift) changing the
white point of the LED light
The peak wavelength of III-
nitride based LEDs moves
towards shorter wavelengths
(Blue Shift) with increasing
drive current and constant
temperature
19ECEN2060
LED Variations
Manufacturing Variations
• Forward voltage variations
– Bandgap discontinuities
– Variable ohmic contact losses
– Low p-type conductivity
– Parasitic voltage in n-buffer layer
• Dominant Wavelength variations
– Crystal and junction growth defects
• LED Flux output variations
– Crystal defects resulting formation of
phonons and non-radiation energy transfer
• LEDs commonly “binned” for wavelength,
light output and forward voltage, all at rated
current
20ECEN2060
Drive circuits for LED’s
• DC current source drive
� Adjustable for dimming
• Challenges
� Voltage drop variations
� Wavelength and flux output variations
� Variations with temperature, the need for cooling
21ECEN2060
Cost of Light: ENERGY!
Labor
13%
Parts
4%
Energy
82%
Disposal
1%
Total Cost of Light
• Required illumination: L [lm]• Lamp cost: k [$/lm]• Efficacy: h [lm/W]• Lamp lifetime: t [hours]• Total time: t
total[hours]
• Cost of electricity: c [$/kWh]• Neglect labor cost (installation, replacements)
Total cost: c*(L/h)*ttotal + L*(ttotal/t)*k
Cost of energy Lamp cost
# of replacements