Introduction to Energy Efficient Lightingecee.colorado.edu/~ecen2060/materials/lecture_notes/Lighting_intro.pdf · Natural gas absorption chillers/heaters Variable speed drives on

Introduction to Energy Efficient Lighting

ECEN 2060

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

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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)

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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

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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

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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

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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)

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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)

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Comparison of Lighting Technologies

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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

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• 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

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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)

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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

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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

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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

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DOE SSL Program LED Targets

DOE, SSL 2008 Multi-Year Plan R&D Update, 1/30/2008

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LED Materials and Wavelengths

White LED: Blue + phosphor

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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

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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

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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

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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