The brightness of an electric light is measured in lumens. A 60 watt incandescent light bulb has a brightness of 800 lumens. The efficiency of an electric light is measured in lumens per watt. Incandescent light bulbs have an efficiency of 15 lumens/watt which means they convert 2% of their energy into visible light. Cfl (compact fluorescent) light bulbs have an efficiency of 55 lumens/watt. A 14 watt Cfl bulb can be just as bright as a 60 watt light bulb. The latest LED lights are more energy efficient still, giving efficiency of up to 100 lumens/watt and a 9 watt LED can be just as bright as a 60 watt incandescent light bulb.
The traditional incandescent bulb has a fragile filament which often shatters when you turn it on. This gives it a relatively short life of 1,000 hours. Cfl bulbs are capable of 10,000 hours and LED lamps are capable of 25,000 hours. Some LED bulbs last so long they come with a 5 year guarantee. If you pay between £5 and £10 for the latest LED bulbs they do last several times as long as a standard light bulb as well as using a lot less electricity.
One other thing to be aware of with LED lights is the colour temperature. This has nothing to do with the brightness or the efficiency of the light bulb but refers to the exact colour of the white produced. There is a scene in a television programme from the 1970s in which a woman complains that the dress she has bought is a horrible colour when she takes it outside into the daylight. Early fluorescent lighting had a terrible glaring white colour. This is reproduced by some of the brightest LED lights. Some manufacturers recommend the use of their most efficient lights in places like the kitchen, where a white glaring colour is more acceptable. Colour temperature is measured in Kelvin. 2700K is warm white, equivalent to an incandescent bulb, 4000K is equivalent to daylight, 5000K is cool white and 6400K is glaring white, equivalent to early fluorescent lights but more efficient.
What would my advice be? Buy LED lights but be aware of the colour temperature. It might be better to sacrifice efficiency and fit a particular 85 lumens/watt warm white bulb (2700K) instead of a particular 95 lumens/watt bulb (6500K) which would be too glaring white for parts of the house where the colour of the light would be really important. Many of our customers avoid low energy lights because they expect an inferior colour. Careful consideration of the colour temperature can avoid this problem.
In 2019 a new version of SAP will be introduced which allows you to achieve a lower CO2 rating by specifying LED lights. Present day SAP 2012 only has one setting for low energy lights.
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