Future Trends in Lighting : Solid State Lighting

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Future Trends in Lighting Solid State Lighting

• W.N. Wang
• Department of Physics, University of Bath

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Acknowledgement

• My grateful thanks go to
• Drs Philip Shields, Sergey Stepanov, Margaret
  Hopkins, Jacky TL Tseng, Graeme Moore, and Mr
  Evgeny Zhirnov, Mr Alan Gott in the growth,
  characterisation, and fabrication of GaN devices.
• Miss Lisa Chens patience, and invaluable
  assistance
• Mr Bob Draper invaluable help on all technical
  fronts.
• My collaborator in Ioffe Physical Technical
  Institute-Prof Y. Shreter, Y. Rebane, Dr. V.
  Bougrov. Prof H.P. Hsieh, National Chiao Tung
  Univesity, Taiwan.
• My collaborator in EE Drs Jay Sarma, and
  Federica Causa.
• Presentation materials provided by Autotype, POC,
  and Bfi OptiLas.
• Most of all, I am very grateful to the support of
  my wife Mary, and two good boys Joshua and Kai.

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Contents

• Introduction
• What is light emitting diode (LED)
• Applications
• The Impact of solid state lighting
• Solid State Lighting Targets
• Generating White Light Using LEDs
• Optimizing the Light Extraction from LEDs
• Light Management Using Optical Design

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What is light emitting diode-LED?

• ?? -An LED is a compound semiconductor device (a
  solid crystalline substance that has electrical
  conductivity greater than insulators, such as
  wood, but less than conductors, such as metal)
  that converts electrical energy directly into a
  discrete color of light.
• -LEDs are made in chip fabrication factories
• -The diode is made from different materials and
  substrates
• -Compounds produce unique colours
• Gallium Nitride blues greens
• Aluminum Indium Gallium Phosphide reds
  yellows
• Aluminum Gallium Arsenide red

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Band diagram illustrating the non-radiative and
radiative recombination
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LEDs made from different materials
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LEDs
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LEDs
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• God Slumbers in the rock.
• He sparkles in the crystals.
• He breathes in the plant.
• He dreams in the animal.
• He awakens in the man.
• Indian proverb cited in Crystal Growth Pergamon
  Press, by Brian R. Pamplin

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Current Applications of Solid State Lighting

• Backlighting for mobile phones and other LCD
  displays (40)
• Large signs and full-colour displays (23)
• Interior and exterior automotive lighting (18)
• Illumination (5)
• Signals (2)

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What is Happening to Traditional Lighting?

• ?? Lighting is the last refuge of analog
• -The lighting industry is transforming into the
  digital
• age
• ?? Its tubes to transistors time for lighting
• -Due to semiconductor-based light sources
  light emitting diodes (LEDs)
• ?? A whole new light
• -Lower energy usage
• -New uses for light
• -New control of light
• -New forms of light
• -Integrated with other digital forms

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The LED Advantage

• ?? Ultra long source life
• ?? Low maintenance
• -Eliminates the cost of replacement lamps,
  gels, filters
• -Reduced labour and maintenance fees over the
  life of the product
• ?? No moving parts
• -No motors or fans that break and need repair
• ?? Low power consumption
• -Extremely low power draw means lower operating
  costs direct and indirect
• ?? No UV radiation
• -Illuminate fabrics and precious art
• ?? Little heat no radiated heat from light
• -May illuminate confined spaces or be adjacent
  to displays and people.
• ?? No noise
• -No buzzing, humming, or fan/engine
  distractions
• ?? Natural coupling for digital control
• ?? Fast acting

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Energy The Future of Solid State Lighting

• By 2025 Solid State Lighting could reduce global
  energy use for lighting by 50.
• Cumulative savings potential in the US alone from
  2000 to 2020
• - 16.6 quads (760 GW) of electrical energy
• - Alleviate the need for 133 new power stations
  (1000 MW each)
• - Financial savings of 115 Billion (1998
  dollars)
• Traffic Light operations cost example
• - LED 2/yr
• - Incandescent traffic light 16/yr
• - Potential 200M annual savings for US traffic
  lights.
• Market penetration estimates
• - 20 of all illumination by 2010
• - 90 of all illumination by 2020

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Progress of LEDs
Efficiencies of conventional lighting are
leveling off, but LEDskeep accelerating. Over the
last 4 decades, there has been a 1,000x increase
in the output (in lumens) of LEDs.
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Trends The LED Cost and Performance Curve

• LED are riding and exceeding the silicon cost
  curve, following a principle similar to Moores
  law
• 30x increase in performance (light output) per
  decade
• 10x decrease in price in the same decade

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Health Issues of house-lighting and Color
Rendering

• Using LEDs for house lighting opens new era for
  healthy and human-friendly lighting. The results
  of recent medical research showing drastic effect
  of light quality on health and lifetime of human
  and animals.
• Light quality is one of the most important aspect
  of LED lighting which has a significant advantage
  over conventional lamps related to a principal
  possibility to
• obtain very high quality light with color
  rendering index (CRI) up to CRI100 compared to
  CRI60 for best conventional lamps.

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Studies on light and health

• One study by John Ott, Ph D dramatizes the
  importance of balanced, high quality light. It
  placed mice under
• four different types of light. In an
  otherwise identical, controlled environment,
• - Under pink fluorescent light, the mice lived
  an average of 7.5 months,
• - Under cool white (standard office)
  fluorescents, the mice lived 8.2 months,
• - Under full spectrum fluorescents with
  balanced, trace ultraviolet, they lived 15.6
  months, and
• - Under natural sunlight, they lived 16.1
  months.

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Studies on light and health

• The Department of Education of Alberta, Canada,
  conducted a two year study involving five schools
  and four different kinds of light. The study was
  conducted by physicians, educators, social
  workers, nutritionists and dentists. The null
  hypothesis stated that the type of light had no
  differential effects on students' scholastic
  achievement, growth and development, attendance,
  and dental histories.
• The study found that students under full spectrum
  light with trace ultraviolet
• - Learned faster
• - Tested higher
• - Grew faster
• - Had 1/3 fewer absences due to illness
• - Had 2/3rds fewer cavities than expected
• "These findings support the conclusion that
  lighting systems are not neutral-they have
  non-visual effects on people who are exposed to
  them over long periods of time.

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Studies on light and health

• A winter study of veterans in a Soldiers' Home in
  Massachusetts compared calcium absorption under
  two lighting systems.
• - Calcium absorption increased 15 per cent
  under full spectrum light.
• - Calcium absorption decreased 25 per cent under
  standard light.

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Studies on light and health

• An early study on the effect of ultraviolet
  radiation on physical fitness was done at the
  University of Illinois.
• The ten week controlled study compared men on a
  five item muscular endurance test and on the
  Schneider cardiovascular fitness index. The
  twenty-two subjects were from the lower third of
  basic physical fitness classes.
• - The experimental group gained 19.2 on the
  Schneider cardiovascular index compared to 1.5
  for the control group.
• - The experimental group gained 15.4 in motor
  fitness compared to the 11.8 for the control
  group.
• - The experimental group had ten colds compared
  to twenty for the control group.
• W. E. Hathaway, J. A. Hargreaves, G. W. Thompson,
  and D. Novitsky, "A Study Into the Effects of
  Light on Children of Elementary School Age-A Case
  of Daylight Robbery," (Edmondton, Alberta,
  Canada Alberta Education, 1992).
• H. M. Hodkinson, B. R. Stanton, and P. Round, et
  al., "Sunlight, Vitamin D and Osteomalacia in the
  Elderly, Lancet 1(April 28, 1973) p. 910.
• R. M. Allen and T.K. Cureton, "Effects of
  Ultraviolet Radiation on Physical Fitness,"
  Archives of Physical Medicine (Urbana, IL
  October 1945) pp. 641-44.

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Colour Temperature (CT)
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Yumic White LED for Endoscopy
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Impact of CRI on Surgical Efficacy

• New OYGB LED source developed with CRI equivalent
  to Halogen

Halogen BY LED OGBY LED CRI gt 90 CRI lt
30 CRI gt 90
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UV Light to kill the Bugs
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Endoscopic Pill Prof Amano
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Emerging Commercial Applications

• Application Light Type(s)
• Skin Treatments Visible UV
• Anti-Cancer PDT Red NIR
• Surgical Lights White good CRI
• Examination Lights White good CRI
• Dental Lights White CT and CRI
• Dental Curing Blue mixed wavelengths
• Endoscopy White and UVA
• Sterilisation/Disinfection UVC
• SAD Whitespecial wavelengths
• Diagnostics UV fluorescence white
• Surgical Dental Headlights White

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Commercial Medical White Light Sources

• Panasonic EverLEDS
• Toshiba TLEDs

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LED Surgical HeadlightsDr ShimadaSurgeon,
Pioneer and Entrepreneur

• Key requirements
• Reduce heat load in operating theatre
• Provide untethered lighting solution
• Reduce shadow issue
• Stable colour temperature
• High CRI
• Portable and Very Bright

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Dr Shimada Surgeon Entrepreneur

• Taking advantage of advancement in white LED
  efficiency

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Dr Shimada - Prototype Build
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Dr Shimada In Action
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LSD PRODUCT
DTF Directional Turning Film
LSD KITS
VLSD Variable (angle) Light Shaping
Diffuser
Vlsd
CTR Circle To Rectangle
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Uses with a Camera
A camera operating under low lighting conditions
over exposes the (centrally) illuminated section
and in consequence under exposes the remainder
of the subject area rendering the usable image
quite narrow.
Using a circular diffuser the imbalance is
eliminated, thus resulting in a good quality
image.
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Summary Branding and new uses of Illumination

• ?? LEDs give a great deal of freedom to the
  designer
• ?? Proximity to materials
• ?? Geometry of housings can be flat and small
• ?? Form factor can be any shape
• ?? Differentiate appearance
• ?? Incorporate styling
• ?? Surfaces can be formed with pockets
• ?? Lighting can be integrated directly into
  surfaces