LED Basics: Technology Fundamentals for Novices · PDF file7/22/2010 · LED Basics:...

ssl.energy.gov eere.energy.gov0

LED Basics: Technology Fundamentals for Novices

2011 DOE SSL Market Introduction Workshop Michael Poplawski

Pacific Northwest National [email protected]

Seattle, WAJuly 22, 2010


Format• 20 minutes presentation• 10 minutes Q & AObjectives• 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)

LED Basics


1) Value Proposition2) Physics3) Photons4) Heat5) Voltage, Current & Time6) White Light7) Directionality8) Lumen Maintenance9) Thermal Management

10) System11) Packages12) Power Control13) Dimming14) Efficiency15) Efficacy16) Lifetime17) Cost18) Learning Curve

2010: 18 Key Fundamentals

http://http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/poplawski_basics_philly2010.pdf


1) Terminology2) System3) Physics4) Photons5) Voltage, Current & Time6) Spectral Power7) Directionality8) Heat9) Thermal Management

10) Thermal Ignorance11) Electric Loads12) Power13) Compatibility14) Lifetime15) Oversimplifications16) Interdependencies17) Marketing Hype18) Life Cycle

2011: Another Spin


• Efficiency, Efficacy = Desired Output / Input– Efficiency = no unit change (%)– Efficacy = unit change (e.g. watts in, lumens out)– LED efficacy (lm/W) = luminous flux (IF, TJ) / IF x VF (IF)– System efficacy (lm/W) = LED efficacy (lm/W) x Electrical

Efficiency (%) x Optical Efficiency (%)

• Power– Power source– Power supply– LED control circuitry– LED driver

1) Terminology

IES RP-16-10: “Nomenclature and Definitions for Illuminating Engineering”


• 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

2) System

PackagePower Control

Secondary Heat Sink

Secondary Optics DiffuserDimmer50/60 Hz


• 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.

3) Physics

P ND

eple

tion+

+++ -

---

P N++++ -

---

P N

Dep

letio

n++++ -

---

+- -+

Zero bias Reverse bias Forward bias

~ No current ~ No current High current

----+

+++


• 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.

4) Photons

Source: LED Transformations

electron hole photon


• Luminous flux is a non-linear function of LED current (IF)• LED current is a non-linear function of forward voltage

(VF)• 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

5) Voltage, Current, & Time

PWM Dimming


• 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

6) Spectral Power

Cool White

Warm White

Source: Cree data sheet

Source: Cree data sheet

Blue LED Yellow Phosphor


• 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

7) Directionality

Visible Light

Visible Light

Visible Light

Heat Heat Heat

Visible Light

Visible Light

Heat

HeatHeat

Visible Light

Visible Light


• 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.

8) Heat

Source: LED Transformations

electron hole heat


• The key to LED lifetime• Manufacturers typically define maximum rated LED

junction temperature (TJ)– 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

• TJ must be managed in system design & installation– LED power– Thermal path between the LED junction and ambient– Ambient temperature

9) Thermal Management


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


• 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

11) Electric Loads


12) Power

Vrms = 120V?

Vrms = 120V?

Vrms = 120V?

Vrms = 120V?

Same Different

Black Box

(average) light output

Black Box

Black Box

Black Box


• 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)

13) Compatibility


• Lifetime is a statistical metric– How is it calculated?– Statistical significance

• Mean? Median? Byy?• B50 = median = traditional source “rated life”

• Warranty is conditional metric– What are the terms?

• System lifetime is what matters– Lumen Maintenance (L70)– 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)

14) Lifetime


• 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

15) Oversimplifications


16) Interdependencies

When you are buying or specifying LED lamps/luminaires, make sure you know what parameters the manufacturer prioritized

Number of LEDsCost

Flux

Efficacy

Current (IJ)

Lumen Maintenance

Color shift

Temp (TJ)

DriverRequirements

ThermalManagement


• 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

17) Marketing hype


• 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.

18) Life cycle

http://www.osram-os.com/osram_os/EN/About_Us/We_shape_the_future_of_light/Our_obligation/LED_life-cycle_assessment/index.htmlhttp://randd.defra.gov.uk/Default.aspx?Menu=Menu&Module=More&Location=None&Completed=0&ProjectID=16519#RelatedDocuments


• Disruptive technology• Innovation ongoing in all

system areas • Get Smart. Ask

questions. Validate information.

Using LEDs, Fact Sheets• ssl.energy.gov/ssl_basics.html• ssl.energy.gov/factsheets.html • Ongoing updatesTechnical Reports• Program Plan:

http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/ssl_mypp2011_web.pdf

• Manufacturing Roadmap: http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/ssl_manuf-roadmap_july2010.pdf

• Energy Savings: http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/ssl_energy-savings-report_10-30.pdf

Conferences• R&D, Manufacturing, Market Intro:

ssl.energy.gov/conferences.html

Evolving learning curve

http://www1.eere.energy.gov/buildings/ssl/conferences.html�


Questions?

LED Basics: Technology Fundamentals for Novices2011 DOE SSL Market Introduction Workshop

LED Basics: Technology Fundamentals for Novices · PDF file7/22/2010 · LED Basics:...

Documents

Transcript of LED Basics: Technology Fundamentals for Novices · PDF file7/22/2010 · LED Basics:...