Choose LEDs - Save the World! Geoff Archenhold's reply "Figure 2 Residential C02 emission, 22% attributed to lighting and appliances, elsewhere in the text 16% of total domestic energy is used by lighting, this is credited to the European Comission - DG Joint Research Centre. later in the same section the 22% figure is used, does this mean that 6% of the domestic energy use is by miscellaneous toasters, hair driers, curling tongs, iPODs, etc?" Unfortunately the reader may have overlooked the fact that one cannot simply deduct percentages to get an answer especially when the percentages may relate to different metrics. For example, the CO2 emission percentages stated within figure 2 for lighting and appliances would most likely include multiple energy sources such as Solid-Fuels, Petroleum, Gas and Electricity as is common with most DTI reports. Each of these energy sources produce electricity to power lighting however certain sources are more CO2 friendly than others which is why there are numerous debates over which is the cleaner electricity generating technology Nuclear, Gas, renewable or Coal!. Each electricity generation method will have certain CO2 conversion rates making it unsuitable to simply subtract the percentages. A really good example of this would be the worked commissioned by British Gas entitled "Domestic Carbon Dioxide Emission for Selected Cities" detailing the KW/h consumption by energy type for large cities in the UK. They cite conversion factors of 0.187, 0.441, 0.2508 and 0.33 kg CO2 / kWh for Gas, Electricity, Oil and Coal respectively. The idea of utilising Figure 2 was to demonstrate to the reader that lighting contributes a significant amount of CO2 production within the UK household and therefore we all have a responsibility and can play a part to reduce this where possible. "There are consistent references to LED energy saving light bulbs. These do not exist. In fact the article states as the last bullet point that LED based light sources which produce 60-70 Lumens per Watt wall plug efficiency need to be developed!" The article was written on the premise that LED technology has the potential to create highly efficient LED energy saving light bulbs and although there are only a few examples available to the consumer on the high street today they tend to be based on older low-power LED technologies. It is hoped that regular readers of the column have grasped that the rapid increase in high power white LED efficacy (now 100lm/W for cool-white LEDs) has meant that it is today possible to create energy efficient light bulb replacements using LEDs. This is certainly evident with a variety of fixture manufacturers including Marl International, Lighting Sciences Group and Edison Opto who have all produced energy efficient MR-16 equivalents found predominantly in kitchen and bathroom installations. These LED products significantly outperform their halogen equivalents and are readily available directly from the manufacturers. The last bullet point referring to light sources that meet a minimum of 60-70 lumens refers to an issue the author has been attempting to highlight to the general lighting community and government-related bodies for some time. By ensuring all LED-based lighting products meet a minimum wall-plug efficacy of between 60-70 lumens it will ensure that conventional light sources such as CFL's, Halogens and incandescent bulbs will not be able to be used in the future. Currently, building regulations such as Part L2 strive for at least 45 lamp lumens efficacy within certain lighting circumstances. This has been an excellent starting point for removing poorly performing conventional lighting technologies however the author is suggesting that in order to remove CFL's and Halogen's from the marketplace as well as encouraging the use of more energy efficient technologies the efficacy should be raised to 60-70 lumens per watt so as to exclude them. In addition many of the current conventional-based lighting sources do not take into account Power Factor Correction energy losses (eg; typical CFL's have only a PFC of 0.6) and less than 50% of the light generated by a CFL is useable therefore reducing the real fixture efficiency significantly. Today, there are LED solutions that already exceed these high efficacies however they do not exist for all lighting applications and therefore further high-lumen light output fixtures should be developed to satisfy the diversity of lighting applications. The figure of 700KWh as the average annual usage of power for lighting is also interesting. Using figures in the article of this representing 16% of energy used this multiplies out at 4,325KWh for total average electricity used domestically, not far from the average of 4,700KWh published by the UK Digest of Energy Statistics, 2005. The comparison to the BMW though is also interesting. Again working from the figures in the article the equivalent CO2 production for a year's total electricity used by a household is produced by driving 11,414.28Km in a BMW 316i, that is 7,134 miles compared with the UK average private mileage of 9,000 miles. The lighting component is equivalent to 1063 miles, therefore the effect in CO2 production of changing to low energy lamps typically is the same as driving 800 miles less per year ! Quite frankly I would rather do this (and I have significantly reduced my car use in town this year by walking and using busses) than lose the ability to light my home with incandescent light sources! Oh another thought, what will be replacing the heat produced by these wasteful incandescent lamps? I guess the extra heat will come from the central heating system, the boiler running that little bit longer each time the heating is used to maintain the same temperature in the rooms! The author certainly would encourage all readers to look at their individual carbon footprints and attempt to make CO2 savings where possible. Unfortunately, not all readers will have the advantage or luxury of being able to reduce their annual car mileage as for example they may live in a rural area of the country not easily covered by public transport or close to local amenities making the car mileage reduction example difficult especially if they are elderly or disadvantaged. The comments of incandescent lamps helping to maintain the temperature within a room and thereby reducing heating energy bills is exceptionally misleading and rather naive. Temperature loss within a room is far more significant through other factors such as heat escaping from windows, un-insulated cavity walls, drafts and a variety of other mechanisms and the heat generated from a 100W light bulb will not be that significant comparatively. Indeed, the author would recommend the reader review table 1 within the Thermal Management article published in February 2007 that indicates an LED produces more effective heat than a 100W incandescent light bulb which by the readers metrics would mean LEDs should help reduce his energy bill (although not as much as I suspect he would like due to the other factors mentioned!). "Finally we have the old tag line of Lumileds having lab demos of LEDs achieving over 100 Lumens per Watt, all very well but until these can be delivered into the market and operate at these efficiencies for prolonged periods at room temperature they remain vapour products! LEDs in the market are fairly stuck around the 20 to 30 lumens per watt range when all the correction factors are taken into account for operating temperature, achieving acceptable life and gear losses and no amount of mythical correction factors for "beam lumens" optical efficiency or other means of goal post shifting spin by LED manufacturers seems to be changing this efficiency figure." As discussed by the author at a presentation at The ARC Show in February 2007 the reader is certainly correct to a degree in that total system efficiency of a LED-based system is lower than that of a single LED. However, the majority of reputable LED manufacturers have responded to early market feedback by adopting more realistic and practicable datasheet information enabling LED fixture designers to better understand the operating performance issues. For example, Philips-Lumileds latest Rebel LED datasheet provides minimum luminous flux values rather than just typical flux values as well as new information stating lifetimes, forward current and operating temperature de-rating curves as discussed in this months LED article. Recently the performance of production available White LEDs has jumped significantly enabling real-life lighting fixtures to be created with high efficiencies. For example, IST Lighting will launch several high-power white and variable-white LED fixtures at euroLED 2007 that are claimed to have a total efficiency of over 40 lumens per watt when generating more than 2000 lumens within a fixture. These figures take into account all system components such as LED driver efficiency, optical efficiency and total fixture efficiency.