Introduction to Energy Efficient Lighting ECEN 2060

Transcription

1 Introduction to Energy Efficient Lighting ECEN 2060

2 US Residential & Commercial Energy Consumption 1 Energy losses during generation, transmission and distribution of electricity * 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! 2

3 Energy Star DOE Initiatives & Programs 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) 3

4 4 Times Square DOE 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 4

5 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 Space Heating Office Equipment Space Cooling Water Heating Miscellaneous Ventilation Cooking 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 5

6 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 6

7 Photopic Vision and CIE Standards Normalized response spectra of human cones, Short, Middle, and Long CIE standard observer color-matching functions 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) 7

8 Background Lighting Energy Definitions 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) 8

9 Comparison of Lighting Technologies 9

10 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 10

11 Discharge Lamp Technologies 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 1-5 mg of mercury per bulb LFL CFL EFL CCFL HID 11

12 Challenges in Discharge Lamps 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) High intensity discharge (HID) lamp ignition example T glow = 4 s Lamp Voltage Lamp Current 12

13 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 Electronic CFL with electronic ballast 13

14 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 14

15 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 15

16 DOE SSL Program LED Targets DOE, SSL 2008 Multi-Year Plan R&D Update, 1/30/

17 LED Materials and Wavelengths White LED: Blue + phosphor 17

18 Color Shift: Current and Temperature Effects The peak wavelength of IIInitride based LEDs moves towards shorter wavelengths (Blue Shift) with increasing drive current and constant temperature The spectrum of LEDs shifts towards longer wavelength with increasing temperature (Red Shift) changing the white point of the LED light 18

19 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 19

20 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 20

21 Cost of Light: ENERGY! 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) # of replacements Total cost: c*(l/h)*t total + L*(t total /t)*k Cost of energy Lamp cost Labor 13% Parts 4% Disposal 1% Total Cost of Light Energy 82% 21