Lighting accounts for 20%1 of all electrical energy usage in offices, homes, transport systems, and retail. About a decade ago, lighting technology was revolutionised by the breakthrough of solid-state lighting (SSL) based on light emitting diodes (LEDs) made from compound semiconductors. Their unique properties such as robustness, long lifetime, colour, tunability, instant on/off and already quite high efficiency will propel LEDs into a new era where they have the potential to outperform all other light sources even in general lighting. By replacing inefficient or environmentally harmful conventional light sources, LEDs will contribute significantly to a sustainable energy saving and reduction of CO2 emissions in the future.
Gas filled fluorescent tubes currently set the standard for efficient indoor/outdoor lighting. However, they suffer from several critical disadvantages, which can be much worse in the "compact" fluorescent format. These include: very slow start-up, difficult to use in cold/outdoor applications, shortened lifetime, flicker, not-dimmable, contain toxic chemicals (mercury, so have important disposal issues), poor colour rendition (multiple phosphors can give "daylight" colour but with reduced efficiency).
Recent and continuing advances in engineering design and the development of new materials present both a significant commercial opportunity and a considerable challenge to the LED-based lighting solutions. LED lamps are now capable to offer comparable light power (lumen) output and have started to compete with other established lighting technologies on the basis of total cost of ownership (TCO). The market is in a state of flux as utilities, energy efficiency organisations, and customers look for optimum solutions that save energy, minimize the cost of ownership, and give acceptable quality of light. Customers are in the process of being educated about comparing total cost of ownership rather than the initial price of lamps.
At present Europe is the leader in SSL technology, from LED development through to full illumination system design and specialist manufacture, with large companies and many SMEs present throughout the supply chain. Major EU players like OSRAM and Philips are at the forefront of innovation in LED technology for illumination systems.
Worldwide sales of High-Brightness (HB)-LEDs for illumination (about 12% of the total LED market in 2009) grew in 2009 by 27% to 470 million Euros2. At the end-user level, the LED-based lamp replacement and luminaire market, which reached ~2.1 billion Euros in 2009, will grow 35% in 2010. Among the market drivers is the fact that major retail firms including the likes of Starbucks and Wal-Mart are currently adopting retrofit projects to replace their existing lighting with LED-based systems
3.
With respect to this, Strategies Unlimited, the world's acknowledged authority on the LED market (www.strategiesinlight.com), appreciated in a 2009 review that "..LED lighting is a technology with great potential to offer energy efficiency, control and flexibility without compromising the quality of light. Based on these attributes, the LED lighting market is forecast to grow at an average annual rate of 45% in the next five years..".
A broad penetration of LED light sources into the market, however, can only be reached if the efficiency and power (lumen output) is further increased, and the costs are significantly decreased to justify the acquisition based on Total-Cost-of Ownership.
For many applications, in addition to high electrical energy to light conversion efficiency it is essential that light sources produce high quality Colour Rendition (CR). This means that the light is produced with the correct intensity to match natural lighting (Colour Rendition Index (CRI) = 100) over the whole visible spectrum, which will give the optimum definition for normal human vision. When the CRI falls below 80, viewing objects by eye will not result in seeing the true colour. As a comparison, incandescent lights typically have a CRI above 80, while standard cool fluorescent lights have a CRI in the range of 60-65. This is considered a poor colour rendering by all standards and it has been shown to be critical to the health and productivity of workers.
White HB-LED's suffer from the same problem, poor colour rendering,due to the fact that the green and red components are weak4. Sunlight has output at all visible wavelengths with relatively gradual and smooth transitions over the entire spectrum. All colours can be determined equally well in sunlight. With fluorescent lamps and phosphor-pumped white LED's there is no smooth output-versus-wavelength transition like for natural sunlight, hence the colours viewed by the eye will not be true5. In application where colour matching is important this is a very serious limiting factor. Moreover, tuning the colour rendition can give further benefits to illumination applications for hospitals (surgical theatres) or retailers (enhancement of visual appearance of displayed items).
1 Energy Savings Potential of Solid State Lighting in General Illumination Applications 2010-2030. Prepared by Navigant Consulting, Inc. for the Department of Energy. Washington D.C. February 2010. Available at: http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/ssl_energy-savings-report_10-30.pdf. see
also, Department of Energy,
http://www.eia.doe.gov/emeu/recs/recs2001/enduse2001/enduse2001.html
2 Strategies Unlimited, "High-Brightness LED Market Review and Forecast 2009", Report OM-50,2009
3 Lighting in Commercial Buildings,
http://www.eia.doe.gov/emeu/cbecs/cbecs2003/lighting/lighting1.html
4 "Light Sensitivity, Scientific Committee on Emerging and Newly Identified Health Risks" (PDF). Director-General for Health and Consumers, European Commission. 2008.
5 The importance of the CRI for well-being and perception is dealt with in the following document: http://www.lexedis.com/download/CRI_IndeXED_90_rev2_11.07_en.pdf
