The amount of energy consumed by lighting systems is significant, estimated, in 2005, at 2600 TWh (terawatt-hours) or 19% of total global electricity consumption. Over the last decade it is estimated that global demand for artificial light grew at an average rate of 2.4% a year. In terms of lumens, not electricity consumed, about 12 % lighting is used for outdoor lighting, 15% for residential lighting and the remainder for commerce and industry.
In commerce lighting accounts for around 40% of electricity consumption while in industry it is about 10%. It is estimated that about 35% of this electricity could be saved by re-lighting or efficient use of lighting. Savings are possible in every sector - the average lighting system had an efficacy of about 18 lumens per watt (lm/W) in the early sixties, by 2005 it reached 50 lm/W.
This application note discusses the requirements for lighting in commercial buildings and the characteristics and the efficiencies of available light sources.
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