NRC Committee on Assessment of Solid State Lighting...John G. Kassakian, Chair – Massachusetts...

National Research Council Committee on the Assessment of Solid State Lighting

DOE Solid State Lighting R&D Workshop Long Beach, CA

January 29, 2013

Division on Engineering and Physical Sciences Board on Energy and Environmental Systems

Dr. John G. Kassakian, Chair

Committee Task Congress requested this study in the 2007 energy bill

(Energy Independence and Security Act of 2007).

Task statement developed by Congressional staff, staff and members of the Academies’ Board on Energy and Environmental systems, and Jim Brodrick of DOE.

Objective and independent assessment of the current state of solid-state lighting technologies and their future potential impacts, including for meeting the new minimum efficiency standards for lighting.

Division on Engineering and Physical Sciences Board on Energy and Environmental Systems 2

Committee Members John G. Kassakian, Chair –

Massachusetts Institute of Technology

Ines Azevedo – CMU Nancy Clanton – Clanton &

Assoc. Wendy Davis – NIST and

University of Sydney Paul A. DeCotis – LIPA Seven P. DenBaars – UCSB

Michael Ettenberg – Dolce Technologies

Stephen Forrest – U. Mich. Pekka Hakkarainen – Lutron

Electronics Evelyn L. Hu – Harvard Gary Marchant – ASU Nadarajah Narendran – RPI Maxine Savitz – Honeywell Michael G. Spencer - Cornell


EISA 07 Section 321 Goals

SSL will be able to achieve these goals.


Principal Findings Improvements in efficacy are highly leveraged.

Color consistency needs improvement.

LED lifetimes appear to be on target, but life of electronics is an issue.

Response of LED lamps to dimming is inconsistent.

Consumer education is important.

Cost is still an obstacle to deployment.


Typical Gallium Nitride (GaN) LED


Typical LED Module

Bush, 2008


White Light Mechanism Tradeoffs


Between Efficacy and Color Rendering Index (CRI)

Source: Pimputkar et al., 2009

Metrics and Standards

Parametric dependencies of LED performance make existing measurement standards inappropriate.

Need standards applied at different “system” stages

Lifetime of luminaires.

Replacement for CRI.

Need aggravated by large number of small manufacturers.


LED Technology Challenges

Continuing need for parametric binning of LEDs. Fundamental materials and growth issues.

Substrate mismatch. Current and thermal droop. Internal quantum efficiency (IQE) and light extraction. High thermal load. Poorer efficacy of low color temperature (CT) lamps. Compatible behavior of RGB/RGBY LEDs.


Binning and Substrate Mismatch

Sapphire and silicon carbide (SiC). currently used substrates for GaN active layer. GaN substrates would eliminate crystal

defects. Metalorganic chemical vapor deposition

(MOCVD) epitaxy process control.


MOCVD Process


Susceptor

Exhaust

Rotation Mechanism

Gas Injection Flange

Thermocouple(s)

Group III (Dopants)

Group V (Hydrides)

Main Carrier Gas

Water Cooled Wall

Stationary Two Zone Resistive Heater Gas flow

Recommendation Fund research to develop instrumentation for

in-situ monitoring and dynamically controlling the MOCVD growth process.

Make a long-term investment in the development and deployment of GaN substrates.


DOE Roadmap Goals for Efficiency

Source: U.S. DOE, 2011a Table 2.1, p. 71


IQE: Internal Quantum Efficiency – How much light is generated inside the LED device. EQE: External Quantum Efficiency – How much of the generated light leaves the device

Projected Cost Trends


Recommendation

Continue to make investments in LED core technology and fundamental emitter research.

Portfolio should be extensive enough to ensure targeted goals of device performance can be met.


Organic LED (OLED) Technology with considerable appeal: Large area planar light source. Tunable color. High IQE.

Very successful in display applications. Adapting technology to lighting a big challenge. Nothing of practical commercial significance presently

available.


White OLED (WOLED) Structures


OLED Technical Challenges Light extraction requires improvement.

Some potential solutions.

Aggressive current droop makes high lumen output difficult. 30x display lumens required.


OLED Challenges (cont’d) Degradation of materials and cathode

interfaces due to moisture and oxygen. i.e., the challenge is packaging.

Short lifetime of blue phosphorescent OLEDs. Lifetime a strong function of temperature: ∆T = +10℉ reduces lifetime by up to 30%

Cost.


Progress in OLED Lighting Efficacy


Current Commercial Activities

Large Asia based OLED display manufacturing infrastructure Samsung, LG May be well positioned to enter lighting market

Other companies focused on lighting GE, Osram, Moser-Baer, Philips Levels of effort not clear


OLED Recommendations

Focus on new and existing approaches to increasing light extraction efficiency. Support research to understand the cause of

efficiency droop at high currents and means to mitigate droop trough materials and device designs. Support research in materials and packaging

technologies to mitigate lifetime degradation.


OLED Recommendations (cont’d)

Support pursuit of materials and architectures to increase lifetime of high intensity white OLEDs. Support cost reduction technologies.


LED Lamp Technical Challenges

Lamp-to-lamp color variation Lifetime Glare Flicker Dimming performance Interaction among lamps on a common circuit Limited lumen equivalency


The SSL Lamp

An LED or LED array Secondary optics Heat sink Driver and control

electronics


Effect of Thermal Design on Weight

Source: Narendran (2011)


Electronics and Dimming

Both LED and drive electronics dictate thermal requirements. Electrolytic capacitors are weak link. Small currents produce visible light. Problem for electronic switches and dimmers.


Dimming No change in CT of dimmed LED lamp.

Low operating currents cause problems for TRIAC* based dimmers.

150 million TRIAC based dimmers installed. NEMA standard SSL 6-2011 to address retrofit.

Lighting control industry developing new designs.


*The TRIAC is a semiconductor switch with simple control.

Recommendation

• Industry develop standards for drivers and controls to ensure “dimmable” lamps function correctly.

• Industry should determine the impact of LED drivers on power quality, particularly THD.


Residential Lighting Consumption


0

20

40

60

80

100

120

140

160

180

200

2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

TWh

YEAR

BAU (TWh)

Scenario 1 (TWh)

Scenario 2 (TWh)

Summary • Increases in efficacy have a strong positive

effect on almost all LED lamp parameters, specifications and characteristics.

• Initial cost, not life-cycle cost, remains an obstacle to deployment.

• Dimming performance is inconsistent and deviates from that of incandescent lamps.


Conclusion With continued U.S. Government support and funding, and DOE leadership, the promise of low cost and very efficient solid state lighting could be realized, lowering U.S. energy needs and allowing the United States to be a significant solid-state lighting manufacturer and technology provider.


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