Colin Humphreys Department of Materials University of Cambridge The Science of LEDs UK CEUG, NCR-101 and ACEWG 2012 Cambridge, 10 September 2012 LEDs • Light emitting diodes • Made from solids that emit light • LEDs last 100,000 hours (electronics 50,000) • Light bulbs (incandescent) last 1,000 hours • LEDs fail by slow intensity decrease • Light bulbs fail totally and suddenly Efficiency of a Tungsten Light Bulb • 5% • 95% lost as heat – stays near the ceiling • Light bulbs are 95% inefficient • 79% of global lamp sales by volume Efficiency of a fluorescent tube and a compact fluorescent lamp (CFL) • 25% for long tube • 20% for compact fluorescent lamp (CFL) • CFLs are 80% inefficient and contain Hg – CFLs rapidly replacing tungsten light bulbs – Walmart sold 100 million CFLs in 2011 Efficiency of light sources Incandescent light bulb = 5% (15 lm/W) Fluorescent tube (long) = 25% (80 lm/W) Fluorescent lamp (CFL) = 20% (60 lm/W) White LEDs (350 mA) = 30% (100 lm/W) White LEDs (in lab) = 60% (200 lm/W) Sodium lamp (high P) = 40% (130 lm/W) The Potential of LED Lighting • Electricity generation is the main source of energy-related greenhouse gas emissions • Lighting uses one-fifth of its output • LEDs are poised to reduce this figure by 75% • Lighting will then use 5% of all electricity • Save 15% of electricity • Save about 15% CO2 emissions from power stations (d) US DoE Report • By 2025 Solid-State Lighting using GaN-based LEDs could reduce the global amount of electricity used for lighting by 50% • No other consumer of electricity has such a large energy-savings potential as LED lighting Global Impact of LED Lighting • 560 full-size power plants could close –If 40% of worlds lighting was LEDs HOW DO LIGHT EMITTING DIODES (LEDs) WORK? Main light-emitting materials (d) Internal quantum efficiency (IQE) InGaN/GaN quantum-well LED How to make white light High-power LED package Some LED Applications Kitchen with LED luminaires Kitchen lighting requirements: 1. >130 lm m^-2 on work surfaces. 2. Good colour rendering – food looks natural and see when food is cooked or gone bad Requirements for Home and Office Lighting • High efficiency • Excellent colour rendering • Long life • Low cost What limits the efficiency of GaN LEDs? • Dislocations? • Point defects? • Efficiency droop at high power Electron micrographs of GaN LED on sapphire Lattice mismatch 16% for GaN and sapphire. Dislocation density 5x10^9 cm^-2 Threading Dislocation Reduction 2 µm 4th 3rd 2nd 1st WBDF TEM image, g = <11-20>, edge + mixed TDs Scandium nitride interlayer -- Multiple SiN interlayers -- x dislocation density reduced to dislocation density reduced ~ 107 cm-2 from 5 x 109 to 5 x107 cm-2 Efficiency droop Efficiency vs current density (470 nm LED) 0.20 0.15 0.10 Peak Efficiency Efficiency (a.u.) Efficiency Onset of 0.05 Auger-dominated recombination 0.00 0.1 1 10 100 Current density (A/cm2) What effect correlates with the onset of efficiency droop? • Does some change in the localisation of carriers? • Does the onset of Auger-dominated recombination? • Does carrier leakage from the active region? The Key Issues for SSL in Homes and Offices • Cost – 75 W-equivalent LED costs $40 • Efficiency • Thermal management – Higher efficiency helps • Lifetime – Not a problem for the best manufacturers • Colour rendering Cost of LEDs • Current costs for a white GaN LED – 10 cents for cheapest low power – US$3 for the brightest high power – LED replacement light bulb for 40W incandescent has about 8 LEDs, costs US$30, but saves US$200 in electricity over 50,000 hours • Current costs per klm of LED white light – $20 or more – Cost target for widespread adoption: $5 High-efficiency InGaN/GaN LEDs on Large Area Silicon Substrates Why grow GaN on 6-inch Si? • Compatibility with Si processing techniques using a Si foundry – Should give improved automation and yield – Compare with “hand” processing with sapphire • Lower cost substrates • Growing on 6”, 8” and larger substrates will offer increasing cost reductions • Ease of removal of Si substrate • Lower cost LEDs and other devices Processed full LED on 6-inch Si wafer Processed full LED on 6-inch Si wafer Processed full LED on 6-inch Si wafer LEDs grown on large size Si can provide a low-cost manufacturing route for GaN based solid-state lighting. –Cost reduction 5-10 times Commercial Exploitation • CamGaN set up in Cambridge in November 2010 to exploit GaN on 6” Si LEDs • Plessey Semiconductors acquired CamGaN in February 2012. Hired 3 of my post-docs. • Plessey will manufacture GaN on 6” Si LEDs at their factory in Plymouth: millions of LEDs per week • A UK success story – should reduce the cost of LEDs Global CO2 Emissions from Lighting • Lighting is one of the biggest causes of greenhouse gas emissions • 1,900 Megatonnes of CO2 emissions per year (from power stations for lighting) • 70% of the global CO2 emissions of all cars • 3 times more than emissions from aviation – (International Energy Agency Report, 2006) Title Text The Science of LEDs Colin Humphreys University of Cambridge UK CEUG, NCR-101 and ACEWG 2012 Cambridge, 10 September 2012 Growing value with LEDs in horticulture controlled environments Philips Lighting Horticulture Esther Hogeveen-van Echtelt 10th of September 2012 CEUG 1 We enable health and wellbeing with light “Enrich peoples access to quality plants through timely introduction of meaningful and sustainable innovations in the lighting domain’’ “In horticulture where business complexity is increasing day by day we will take the lead to bring ‘sense and simplicity’ with new lighting solutions and beyond to improve the business of the grower’’ 1 The LED revolution 18% 2011 82% 50% 2015 50% Traditional lighting LED lighting *Source: Philips Lighting global market study 2009, updated for 2010 Oliveira Bridge, Sao Paulo, Brazil Key characteristics LED technology Light Emitted Forward Plastic Lens Sillicone Encapsulent Chip Cathode Lead Solder Connection Gold Wire Reflector Cup Heatsink Slug Heat High power Rebel LEDs High POWER LUXEON LEDs 4 2 No LED is the same Anybody can buy a LED, but can they build a good LED light system? • Every type of LED has his own design rules, disrespect the design rules and the LED system will fail after several hours • Data sheet of a LED for details 5 Key characteristics LED technology The performance of LEDs is determined by: • Heat management • Lifetime (related to light output) • LED type and quality • Binning 6 3 The Philips GreenPowerLED product difference GreenPowerLED Products Enable our HortiLED Solutions. • Best system efficacy • Stable light output, high LED quality • Best in class driver performance * • Long lifetime, clear min. light levels over time • Global Supply Certifications (UL, CSA, CE etc.) • Reliable specification, we set world standards • Cost competitive, Philips LED synergy & volume *High Power factor, low total harmonic distortion Warranty 3 yrs RoHS ISO 9001-2000 ISO 14001 Bio Photo biological safety The value for you X(tra profit) Factors Most effective use of μmol Positive effect LED on other growth factors Value for the grower μmol/W €/m2 Grow light Installation cost efficiency 4 New possibilities with LED Lighting LED adds growing power using less energy AND LED brings additional benefits (X-factors) on top of energy saving vs traditional lighting • better growth as LED light is used more effectively by plants • plant development per crop and growth phase e.g by tuning spectrum • cost savings (temperature, water etc.) because it generates less heat • more plants on less m2 by using layers with light closer to the plants 9 What is a light recipe? A light recipe is an instruction based on knowledge on how to use light to grow a certain crop under certain circumstances to obtain a certain business result Combining: • Lighting aspects: Light level, spectrum, required uniformity level, position and time • Boundary conditions for which the recipe is valid like climate conditions etc. • Results: X-factors besides energy saving found and/or expected 10 5 Finding recipes for plant growth - Step by Step 1st test setup Analyze, adjust Scale-up Fine-tune on and 2nd test best treatment production scale We deliver value with LEDs for growers Vegetables Cut flowers Tuning flowering Potted, Bedding Leafy Vegetables & Plants and Flower Bulbs herbs Perennials 12 Seeds and young Tree Tissue Culture plants nurseries 6 We deliver value with LEDs to research institutes Climate rooms Climate Greenhouse cabinets 13 Our approach: Step by step to your solution Step 1. What is your need? Step 2. Light recipe our know-how and Step 3. Product, installation and application network for your solution Step 4. Business case and Financing Step 5. Agreement, delivery and installation Step 6. Implementation check Step 7. Follow up 14 7 Case: Kreuk- Tulips – multilayer in greenhouse Goal: Increase production capacity Solution: Extra cultivation layer in greenhouse with proven LED recipe. Tulips move in 2 weeks from dark LED daylight LED Benefit: * 3400 m2 cultivation area on 1500 m2 ground area * Improved plant quality (darker green and more elongation) * Lower costs/stem GreenPower LED production module 15 Case: Lutz- Strawberry – control flowering and stem elongation Goal: Induce early flowering and good stem elongation Solution: GreenPower LED flowering lamp Benefit: * Good, reliable elongation of first leaves and trusses and good quality first production * Easy to install * Energy saving (~85%) GreenPower LED flowering lamp 16 8 Case: Delissen- Lettuce young plants