Living with Technology, Volume 2, Issue 6 March 2005 Energy Saving Gets the Green Light Part 3 Barry Jerome, Barry Smith & Chris Walker In Part I, we introduced low energy lighting and described the history of its development, concluding that CFLs (compact fluorescent lamps) were the most convenient form for domestic lighting. This was followed up in Part 2 with a detailed look at CFLs, considering the different types available, their advantages and disadvantages, and how to get the best buys to be able to maximise savings. In this Part, we are looking at the latest developments in low energy domestic lighting and, in particular, focussing on high power LED (light emitting diode) technology. This technology is still at a very early stage but products are emerging which suggest that future efficiencies could be as good as those of sodium lamps and have lifetimes in decades rather than years. But first some updates... Further developments in CFLs As mentioned in Part 2, the drive to produce ever smaller CFLs is focussed on reducing the tube size and improving the performance of phosphors and ballasts. Example lamp sizes comparing a standard GLS and various wattage mini-spiral CFLs The mini-spiral lamps have provided dramatic size reductions, and it's now possible to get a CFL which is actually smaller than its equivalent 'ordinary' (GLS) light bulb. This is the 11W (60W equivalent) mini-spiral CFL. The 15W mini-spiral is only slightly longer than its 75W GLS equivalent, and in overall volume is smaller. 1
Comparison of sizes of an 11W mini-spiral CFL with a 60W GLS light bulb This drive to ever smaller sizes is continuing and should lead to CFL equivalents for most types of incandescent (GLS and halogen) lamps. The CFL spotlight is one area of focus (pun intended!) as they offer advantages of lower heat output in confined spaces, as well as being much more energy efficient. Two-part CFLs A 9W CFL spotlight equivalent to a 40W R63 GLS spotlight Another product advance, which has recently become available, is the 'ultra compact two-part' CFL. This lamp combines, in one design, the advantages of lower cost two-pin CFLs without ballast, and the ease of installation of bayonet (BC) fittings. The lamp comes in two parts: the ballast with BC fitting a two-pin 'tube' which plugs into the ballast When first purchased, the two parts are bought together, but replacement lamps ('tubes') can be purchased separately. The lamps are available in two wattages, 7W and 11W. The 7W tubes are available in various colours (white, blue, red and green). The tubes have a lifetime 2
of 10,000 hours (about 10 years of normal domestic use), but when it wears out, it can be replaced with another tube which plugs into the original ballast. The ballast has a lifetime of 2-3 times that of the tube. The only restriction is that the replacement tube must be specific to the wattage of the original lamp i.e. a 7W replacement tube must be used with a 7W ballast. The coloured tube brings the use of different coloured GLS bulbs to the world of CFL lighting. Two-part CFLs are available from: http://www.yourwelcome.co.uk Dimming Although CFLs aren't compatible with wall dimming switches, four-pin CFLs can be dimmed with suitable high frequency ballast/control gear. A company called Lampholder 2000 (http://www.lampholder.co.uk) has developed a ceiling pendant that is dimmable with a toggle switch to 50% of the light output. It takes four-pin CFLs. It has probably been produced to fit in with the new building regulations on low energy lighting (see Part 2). Another company MLD (http://www.malham.co.uk) has developed dimmable CFL downlighters for conference rooms which can be varied from 10-100% light output. The ballast also has an auto switch-off if the lamp fails. This isn't intended for home use, although products developed for industry often become available for the home within a year or two if prices can be reduced to an acceptable consumer level. High power LEDs The use of high power LEDs for lighting is still at an early stage, but impressive advances are continuing to be made each year in brightness and efficiency. Today, they are nowhere near replacing incandescent (GLS and halogen) or CFL for general domestic lighting, but the numbers of applications are increasing all the time as power and efficiency improves. Predictions are that high-power LED lighting will eventually replace all incandescent and CFL lighting. An example of what can already be achieved is demonstrated in the 'VOS Pad' in Chelsea, but more of that later. High power LEDs already achieve a lifetime of 100,000 hours which is 11 years of continuous use or 60 to 100 years of average domestic use. 3
A red LED traffic light. It uses 15W of power compared with 150W for a normal red incandescent traffic light The two main areas where LEDs are seen today are in signal lights (traffic and railway) and in car lights (mainly indicator and stop lights). The use for signal lights is an ideal application for high-power LEDs because LEDs produce light in a narrow beam - from about 8 to 140. The effect of this narrow beam is to make the light appear much brighter and be visible from much greater distances. GLS all round light vs. LED beam Because of the combination of brightness and efficiency, most states in the US have a plan to migrate all traffic signals to LEDs and, in cars, LED lights are predicted to replace all incandescent lights (including headlights) by 2010. A report prepared last year for the US Department of Energy estimated that, by 2025, if price and performance targets are achieved, indoor and outdoor LED lighting could save the US approximately 114 billion KWh per year. That is the equivalent of the electrical output of 14 large power stations. The accumulative savings from now until 2025 were estimated as reaching somewhere between 505 and 1,848 billion KWh, depending on how rapidly LED lighting is adopted in the marketplace. These accumulated savings were estimated to be worth up to $128 billion. This report, 4
however, is based on today's situation, and a wider adoption of CFLs could achieve some of these savings. A brief history of LEDs The phenomenon of light produced from solid state chemicals (electro-luminescence) was first observed in 1907 by Henry Joseph Round using silicon carbide (SiC). The yellow light produced was too dim to be of practical use and further work was abandoned. In the 1920s, and again in 1936, further research was carried out using zinc sulphide (ZnS) to produce electro-luminescence. Extensive work in Britain in the 1950s eventually led to the first commercial LEDs in the 1960s. These were infrared LEDs, used extensively now for remote controls and illumination for infrared sensitive cameras. It wasn't until the late 1960s and the 1970s that visible light LEDs appeared. These were initially gallium arsenide phosphide (GaAsP) and then gallium phosphide (GaP), to create red, yellow and green light. The first generation of 'super bright' LEDs appeared in the mid-1980s with the use of gallium aluminium arsenide phosphide (GaAlAsP). This was superseded in the 1990s by the introduction of indium into the equation with the use of indium gallium aluminium phosphide (InGaAlP) to produce 'ultra bright' LEDs in orange-red, orange, yellow and green. The first blue LEDs appeared in the early 1990s, using silicon carbide (SiC) - a throwback to the very first observation of electro-luminescence. It was the use of gallium nitride (GaN) and indium gallium nitride (InGaN) though, which produced high intensity green and blue LEDs. The 'ultra bright' blue chips became the basis of white LEDs in which the blue LED was coated with phosphorescent coatings which absorbed the blue and created white light. For LEDs, this has been a slow progression up the light spectrum from infrared to blue. Recently, this has extended even further and there is now an ultraviolet LED. Many companies are involved in research and development to produce brighter and more efficient LEDs. These include traditional lighting manufacturers and semiconductor companies, including Lumiled, GE, Osram, Cree, HP and Nichia. The US Department of Energy (http://www.netl.doe.gov/ssl/highlights.html) is also jointly funding research with various companies to develop better LEDs. In the US, 25% of electricity is used for lighting, and the US Administration sees the adoption of LED lighting as a way of reducing carbon emissions. How do they work? We will try to explain this as simply as possible, but if you prefer not to be concerned about the technical explanation of how the light is created in an LED, skip to the next section on options for light colours. 5
In an LED, light is created by a completely different mechanism from an incandescent lamp or a fluorescent tube. In the incandescent lamp, the light is created by heating a wire until it glows, while in the fluorescent light an electrical discharge across the mercury vapour in the tube creates UV light which generates visible white light when it strikes the phosphor coating on the tube. In an LED, the light is created purely by the movement of electrons in the semiconductor material used to construct the LED. Diodes (including light emitting diodes) are constructed of two types of semiconductor material. One type has additional electrons and is therefore negatively charged (n-type) and the other has a deficit of electrons and is therefore positively charged (p-type). At the junction where the n-type and p-type semiconductors meet, electrons migrate from the n to the p-type and form a non-conducting barrier (the 'depletion zone'). Applying a voltage across the diode, by connecting the negative to the n-type and positive to the p-type, causes electrons to flow from the n-type to the p-type. Atoms in the p-type semiconductor (which have a deficit of electrons) are referred to as 'holes'. The voltage required is normally quite low (less than 5V). When an electron travels from the n-type to the p-type it combines with one of these holes, and when this happens, energy is given off in the form of a photon of light. p-type and n-type semiconductors in a diode The depletion zone acts as a barrier when no voltage is applied. The type of light given off is completely dependent on the chemicals used to construct the LED. In the simple atomic model, negative electrons travel around the positive nucleus of the atom in orbits at various energy levels. When an electron combines with a hole, it is jumping from one orbital to another. The difference in the energy levels of these orbitals is the energy which is given off as light: the smaller the energy difference, the lower the energy of the photon (e.g. infrared), and the larger the energy difference, the higher the energy of the photon (e.g. red, to green, to blue and ultimately UV). When a voltage is applied electrons flow to the ptype region. When an electron combines with a hole a photon of light is emitted. 6
Colour options Different semiconductors have different properties which result in a range of colours which can be generated. Generally, each semiconductor can only be used to generate light in a very narrow part of the light spectrum and each normally has a peak at one specific wavelength of light. The challenge with ultrabright LEDs was to be able to produce white light. Without this ability, LEDs would never compete with incandescent or fluorescent lighting for general purpose use. The four options for producing white light with high-power LEDs White light can now be created using four different techniques, each of which has its advantages and disadvantages in terms of brightness and efficiency. The diagram compares each method. The main type of white LED on sale today uses a blue LED with yellow phosphor, while the most efficient at the moment is the combination of red, green and blue LEDs to produce white light. This type was used in the VOS apartment (see later), but it's more difficult to control the overall appearance of the white light. One additional advantage of using the three colour LEDs is that the colour of the light can be changed by dimming one or more of the coloured LEDs. In this way, the mood of the room being lit can be varied. How efficient are they? There is a broad range of efficiencies for LEDs which varies from worse than incandescent to as good as fluorescent, depending on colour and materials used. The red and yellow LEDs are usually more efficient than green LEDs, which are more efficient than blue or UV LEDs. High efficiency red, yellow and green LEDs are fine for specific applications such as road or rail signals, or car brake lights. It is the efficiency of white LEDs which is important for comparison with other forms of domestic lighting. The best white LED produced to date has an efficiency of 74 lumen/watt, comparable with a fluorescent light source. This efficiency is unlikely to be seen by the consumer in a light bulb, however, as other components needed to achieve the right voltage and current may be needed and will themselves consume electricity. 7
Although the efficiencies of LED lights may not be as good as CFLs, the light is transmitted in a beam which concentrates the light produced into a smaller area. When viewed along this beam, it can appear equivalent in brightness to a much brighter incandescent light bulb, and therefore have an apparently very good efficiency. An incandescent light bulb or a CFL transmits light in a sphere whereas the LED lamp transmits the light in a beam with an angle which varies between about 8 and 140, depending on the materials used and the design of the LED. How does LED lighting compare? At the moment, individual LEDs are very dim in comparison to incandescent or CFL lamps. This is overcome by making light bulbs from multiple LEDs. This results in higher costs and would require large lamps for general bright lighting. The brightest individual LED currently available is the Lumiled's 120 lumen Luxeon Star LED. A Prolight 100 lumen white LED. Notice the different packaging used for bright LEDs compared with the traditional LED shape A 1000+ lumen LED lamp (equivalent to a 60W GLS) has been produced in the laboratory. This is a true 60W GLS equivalent producing 'all round' light from a 50mm diameter spherical bulb, not just a narrow beam of the same brightness. LEDs will need to be much brighter to achieve the predicted general use for car headlights by 2010 (although Lumiled are already claiming their Luxeon Star LEDs are being used in theatre spotlights and car headlights). Once brightness and efficiency are achieved, LED lamps will have many advantages over incandescent and CFL lamps. Particular advantages are that they come on instantaneously, the lamps last 'forever', and they are not easily broken (and no broken glass to cut yourself on). They can also be dimmed and switched on and off frequently without damage. The instant light, vs the delay for an incandescent lamp, is being promoted as a safety feature in car stop lights as it gives approximately 25 feet more warning at 60mph when brakes are applied. 8
What are they being used for today? Apart from the widespread use of infrared LEDs, the main uses of visible light LEDs are for road and rail signal lights and for vehicle stop and tail lights. The use for traffic lights started in about 1996 when all three colours (red, amber and green) LEDs in the correct colours and brightness to meet traffic regulations became available. The city of Philadelphia ran a pilot project to compare costs and, as a result, decided to replace all traffic signals. From their measurements, they expected to save up to $250 per intersection and a total of $1m per annum from saved electricity and maintenance costs. Another area of use in the US which is increasing rapidly is in display signs. LED lighting is replacing neon signs as they are more energy efficient and considerably more robust. The most dramatic examples are the video screens and animated signs that cover the buildings in Times Square in the US. Domestic applications? When first considering extending the articles on low energy lighting to a third part to cover LEDs, the use of LEDs for domestic lighting seemed like a low-profile, niche application. Since then, however, there has been quite a rise in interest, not least in the many types of Christmas lighting available at the end of 2004. The use of LEDs for garden lighting also seems to be taking off, and in my last visit to B&Q, I noticed that they have several LED lights in their garden lighting display. There are many different types of garden lighting available, most of which are low voltage, and include path lights, decking and drive-over lights, spotlights and solar-powered lights. Another area where LED lights are being adopted is in torches. One design (which was bought as a present last Christmas) even included a magneto which, with a little squeezing of the handle, provides bright light for about thirty minutes and gradually dimming light for a further two hours. There is also a lot of interest from caving enthusiasts. LED lights in caving lamps are far less likely to fail from rough treatment. In addition, they can be dimmed effectively without wasting battery life and the beam doesn't need focussing. 9
ES fitting 1W lamp - 13 LEDs GU10 fitting 2W lamp - 38 LEDs ('15W halogen equivalent') BC fitting 2.5W lamp - 45 LEDs ('40W GLS equivalent') Although it's possible to buy mains-powered LED lamps with standard fittings (bayonet BC, screw ES and GU10), little use has yet been made of them for general house lighting. This is probably due to a combination of little visibility in the marketplace and the relatively high cost of lamps. One example of where LED lighting has been used extensively is in the 'VOS Pad', a hi-tech apartment in Chelsea. This is home to Marcel Jean Vos, a Dutch designer and property developer and the chief executive of Vos Solutions. Vos Solutions have been making money from stripping out cheap interiors from modern two-bedroom flats and replacing them with hi-tech luxury fittings for wealthy clients. After experimenting with LED lighting in one or two conversions, he decided to use only LED lighting in the next conversion. The LED lamps used are all red, green, blue arrays. This gives white light when all colours are fully lit, but by dimming the individual colours, the lights can be used to produce a range of lighting effects. The pictures show some of the colour effects and also the approach to lighting the apartment. There are over one hundred light fittings, most of which are set into the floor, with some up and downlighters and others set into worktops. Setting the lights into the floor was only possible because the LEDs generate practically no heat. The lights are mounted around the edges of the floor and shine up the walls to illuminate the walls and ceiling in a reasonably even light. The apartment has a fairly minimalist approach to decoration and furnishing, and would probably not suit the average family home. 10
Internal views of the hi-tech Chelsea apartment designed and fitted out by VOS Solutions. It's lit entirely by LED lighting which can be varied from white through a range of other colours. The dining area in gold light The kitchen area illuminated in blue and white 11
The bathroom in white light The lounge area in magenta The total energy consumption when all lights are on is about 400W. The low power requirements enabled both power and control to be provided by connecting the lights together with Cat 5 networking cable. Although the running costs of the lighting are very low, there was a very high initial cost for installing the lighting of over 30,000. 12
Cost and availability LED lights are mostly available from internet sites. A Google search for 'LED lights' will provide a long list. Some retailers are beginning to stock them, but mainly as garden lights in one or two low voltage or solar-powered designs. LED lighting is still relatively expensive, but dramatic effects can be achieved with appropriate use of LEDs. Several years ago in London, when the Imax cinema was built near Waterloo station, the underpasses were refurbished and individual blue LED lights were installed in large numbers on several walls. It gave quite a magical feel to the passages (like Santa's grotto). At the moment, LED lighting is like many other technologies as far as 'when to buy' is concerned. We know that there will be improvements and that costs will reduce, but when to buy is a personal choice based on the cost versus individual satisfaction received from using it. For general lighting, the total cost of ownership (TCO) of CFLs still makes them the best option today. Lifetime and running costs can make the TCO of LED lighting lower than that of incandescent lights for some specific applications. Areas include garden lighting and special coloured lighting effects in the house. Although initial cost will be higher, the running costs of leaving the lights on for extended periods will be much lower. In addition, because the bulbs will never need changing, the garden lighting units can be very effectively sealed against the weather. The table gives a list of example prices for a range of LED lighting for use in the home. Future developments? The driver for research on LEDs is to increase brightness and efficiency. Considerable progress has been made in both areas, and each year there are significant steps forward. The rate of increase in brightness has been compared to Moore's Law for computer chips - a doubling of the number of transistors on a chip every two years. If this prediction is true then there are enormous improvements still to be achieved. One effect that would be noticed is a reduction in the number of LEDs required for each lamp. At the moment, LED lights use multiple LEDs to give enough light, e.g. a 40W GLS equivalent uses 45 white ultrabright LEDs, and the red traffic light pictured uses 680 red LEDs to be equivalent to a 150W GLS. If Moore's Law applies to LED 13
brightness then the numbers of LEDs needed for each light will reduce rapidly. The effect will be a corresponding reduction in price and size of LED lamps. One possible consequence of a shift to LED lamps could be that we will no longer need a 240V mains supply for our lighting. The VOS Pad has shown the way on this, with the use of Cat 5 networking cable for both power and control of the LED lights. It is quite feasible that a step-down transformer could be situated near the circuit breaker to provide low voltage lighting circuits for the whole house. This would be an important additional safety feature. Organic LEDs Another major area of research is into organic LEDs (OLEDs). This idea was developed by Eastman Kodak in the 1980s and is likely to replace LCD technology for thin film display screens. For lighting, it is at an even earlier stage than LED research, but it's also being jointly funded by the US Department of Energy. OLEDs differ from LEDs in that they use a series of organic (plastic) thin films between two conductors to produce the light. The mechanism of using electrons and holes is the same as for LEDs. The use of a plastic film allows the LEDs to be produced in sheets instead of individually. The disadvantage at the moment is that they are nowhere near as efficient as inorganic LEDs. A collaborative project between GE Global Research and Cambridge Display Technologies made a major breakthrough in 2004. They developed a two-square-foot OLED light panel that produces 1200 lumens of light (equivalent to the light from a 60W GLS bulb) and at an efficiency of 15 lumens/watt (on a par with incandescent lamps). The panel is composed of 16 6" square OLED panels. It was the culmination of a three-year research project which had the goal to produce an OLED light panel with brightness and quality of light comparable to a fluorescent light, and efficiency better than an incandescent lamp. The next goal is to demonstrate that OLEDs can be made cost-effectively on a roll-to-roll process. If OLED development is successful, it will offer a different concept in lighting. It will no longer be necessary to have a point light source for lighting. For example, the walls could have OLED panels or the ceiling could even be papered with OLED sheets to provide even lighting. This is likely to be many years away yet, but if LED research and development follows the predicted advances, then our houses will be lit by a combination of LED and OLED lighting which outlasts its occupants. Light bulbs will be consigned to museums to be viewed alongside Victorian gas lighting. 14
Acknowledgements: 1. Yourwelcome (http://www.yourwelcome.co.uk) for pictures of the two-part ultra-compact CFL and the CFL spotlight 2. Stellatus Lighting Ltd. (http://www.led-bulbs.com) for pictures of mains LED lights and the Prolight LED 3. VOS Solutions Ltd. (http://www.vossolutions.com) for pictures of the 'VOS Pad' in Chelsea Barry Jerome, Barry Smith, Chris Walker This article is the last part of a series of related articles 15