LED Basics: Technology Fundamentals for Novices

Transcription

1 LED Basics: Technology Fundamentals for Novices 2011 DOE SSL Market Introduction Workshop Michael Poplawski Seattle, WA July 22, 2010 Pacific Northwest National Laboratory 0

2 LED Basics Format 20 minutes presentation 10 minutes Q & A Objectives Technology fundamentals Do s and don ts Beware oversimplification Identify and prioritize what you need to learn more about Later Today Lighting Performance Standards (LM-79, LM-80) Products (DOE Lighting Facts, CALiPER) Applications (GATEWAY) 1

3 2010: 18 Key Fundamentals 1) Value Proposition 2) Physics 3) Photons 4) Heat 5) Voltage, Current & Time 6) White Light 7) Directionality 8) Lumen Maintenance 9) Thermal Management 10) System 11) Packages 12) Power Control 13) Dimming 14) Efficiency 15) Efficacy 16) Lifetime 17) Cost 18) Learning Curve 2

4 2011: Another Spin 1) Terminology 2) System 3) Physics 4) Photons 5) Voltage, Current & Time 6) Spectral Power 7) Directionality 8) Heat 9) Thermal Management 10) Thermal Ignorance 11) Electric Loads 12) Power 13) Compatibility 14) Lifetime 15) Oversimplifications 16) Interdependencies 17) Marketing Hype 18) Life Cycle 3

5 1) Terminology Efficiency, Efficacy = Desired Output / Input Efficiency = no unit change (%) Efficacy = unit change (e.g. watts in, lumens out) LED efficacy (lm/w) = luminous flux (I F, T J ) / I F x V F (I F ) System efficacy (lm/w) = LED efficacy (lm/w) x Electrical Efficiency (%) x Optical Efficiency (%) Power Power source Power supply LED control circuitry LED driver IES RP-16-10: Nomenclature and Definitions for Illuminating Engineering 4

6 2) System An LED lamp/luminaire is a system Every component in the system not only adds function (and cost), but often affects the performance of the other components, and can be a factor in determining overall performance and lifetime 50/60 Hz Dimmer Power Control Package Secondary Optics Diffuser Secondary Heat Sink 5

7 3) Physics LEDs are polar semiconductor devices formed by the creation of a P-N junction Current only flows in one direction, under forward bias and the collapse of the depletion region Narrowband light is generated in the P-N junction as a result of current flow under forward bias The wavelength of the light generated depends on the band gap energy of the materials forming the P-N junction. P ~ No current ~ No current High current Depletion N P Depletion N P N - + Zero bias Reverse bias Forward bias 6

8 4) Photons LED photons are generated by electroluminescence (due to electric current), as opposed to incandescence (due to heat). Electroluminescence is the result of radiative recombination of electrons and holes in a semiconductor. electron hole photon Source: LED Transformations 7

9 5) Voltage, Current, & Time Luminous flux is a non-linear function of LED current (I F ) LED current is a non-linear function of forward voltage (V F ) Manufacturers typically define maximum rated LED drive currents LED response time is very fast Allows for PWM dimming Improves potential for control (e.g. occupancy sensing) Can result in undesirable flicker PWM Dimming 8

10 6) Spectral Power LEDs are narrowband light sources Many techniques for making white light Phosphors Downconvert short wavelength (higher energy) to longer wavelength (lower energy) Inefficiency (Stokes loss) Performance degradation over time/temperature Blue LED Source: Cree data sheet Warm White Yellow Phosphor Cool White Source: Cree data sheet 9

11 7) Directionality Omni-directional light External reflector, lens Size dependence Generated heat radiated away (IR) Directional light Internal and/or external reflector, lens Index of refraction change Generated heat transferred by conduction (primary) and convection Heat Visible Light Visible Light Visible Light Visible Light Visible Light Heat Heat Visible Light Visible Light Heat Heat Heat 10

12 8) Heat Recombination of electrons and holes does not always result in electroluminescence Heat is the result of non-radiative recombination of electrons and holes in a semiconductor. electron hole heat Source: LED Transformations 11

13 9) Thermal Management The key to LED lifetime Manufacturers typically define maximum rated LED junction temperature (T J ) Operation at lower junction temperatures results in higher lumen output and/or longer lifetime Light output, lifetime vs. junction temperature relationships (shape of curves) can vary for different LED colors, types, and/or manufacturers T J must be managed in system design & installation LED power Thermal path between the LED junction and ambient Ambient temperature 12

14 10) Thermal Ignorance Do not expect to install your LED replacement lamp anywhere and see equal performance Some manufacturers specify maximum ambient temperatures for installation Exceeding maximum rated temperatures can result in lower lifetime, and/or lower luminous flux 13

15 11) Electric Loads Resistive loads For AC input, only care about Vrms Time independency: Irms = (1/R) x Vrms Incandescent sources effectively only care about Vrms Constant R at steady state R is a function of filament temperature Complex loads Contain devices which store energy (e.g. capacitors, inductors) and/or devices with non-linear current-voltage relationships Time dependency: dv/dt, di/dt, on/off switching LEDs are non-linear devices Different current-voltage relationships in different regions of operation Small change in voltage can equal large change in current (Average) current must (typically) be controlled 14

16 12) Power Vrms = 120V? Vrms = 120V? Vrms = 120V? Vrms = 120V? Same Different (average) light output Black Box Black Box Black Box Black Box 15

17 13) Compatibility The LED driver controls the emission of luminous flux Average value Modulation (flicker) LED driver compatibility with any element (power and/or control) in its electrical path can affect how well it delivers upon its designed performance Transformers, dimmers, etc. Some manufacturers do compatibility testing and generate compatible product lists LEDs ARE capable of high performance dimming Dimming control, power control compatibility is key Systems with separate power and control signals (e.g. 0-10V) minimize compatibility issues MANY variables affect compatibility with systems with coincident power and control signals (e.g. forward, reverse phase) 16

18 14) Lifetime Lifetime is a statistical metric How is it calculated? Statistical significance Mean? Median? B yy? B 50 = median = traditional source rated life Warranty is conditional metric What are the terms? System lifetime is what matters Lumen Maintenance (L 70 ) Color Maintenance Catastrophic Failure Maintenance is still a necessary part of the equation Long life introduces new application-specific considerations Cleaning Increased transient event exposure (e.g. surge) 17

19 15) Oversimplifications Performance LED efficacy is not a constant LED driver efficiency is not a constant Lifetime Lifetime lumen maintenance LED lumen, color maintenance are not constants System System efficacy LED efficacy System lifetime LED lifetime 18

20 16) Interdependencies Driver Requirements Cost Number of LEDs Efficacy Current (I J ) Lumen Maintenance Flux Temp (T J ) Thermal Management Color shift When you are buying or specifying LED lamps/luminaires, make sure you know what parameters the manufacturer prioritized 19

21 17) Marketing hype Do know your value propositions Energy, maintenance savings Light spaces differently (small, color without filters, fast, control) Do your own payback calculation(s) Don t be green-washed 100,000 hour no-maintenance lifetime Legacy form-factor, non-legacy light distribution Efficacy vs. light quality Don t succumb to scare tactics Flicker Blue Light Electromagnetic radiation Hazards may be real, risks are limited 20

22 18) Life cycle Existing studies Use energy dominates (> 95%) total energy (use + manufacturing) for all light sources Incandescent sources consume the most total energy, and have the worst environmental impact, by far SSL is comparable to CFL today Continuing improvements in SSL efficacy will improve its life cycle performance further DOE is re-booting its own LCA study, starting next month, with a new global team including researchers from PNNL, Navigant, and academia

23 Evolving learning curve Disruptive technology Innovation ongoing in all system areas Get Smart. Ask questions. Validate information. Using LEDs, Fact Sheets /ssl_basics.html /factsheets.html Ongoing updates Technical Reports Program Plan: s/publications/pdfs/ssl/ssl_mypp2011 _web.pdf Manufacturing Roadmap: s/publications/pdfs/ssl/ssl_manufroadmap_july2010.pdf Energy Savings: s/publications/pdfs/ssl/ssl_energysavings-report_10-30.pdf Conferences R&D, Manufacturing, Market Intro: /conferences.html 22

24 Questions? LED Basics: Technology Fundamentals for Novices 2011 DOE SSL Market Introduction Workshop 23