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TECHNICAL

This graph shows how rooflight areas will affect illumination levels. In this example for a single storey building located in London, between the hours of 6am and 6pm daily, with rooflights providing 50% light transmission. You can see that as the rooflight area along the bottom of the graph increases, the length of time a given illumination level is achieved, is extended. So for a building requiring 500 Lux, looking at the yellow line, you can see that with 10% rooflights, 500 lux would be achieved for approximately 2000 hours or 46% of the working year. If rooflight area is increased to 15%, 500 lux is then available for just over 2500 hours, or 58% of the working year. So a building with 10% rooflights will require electric lights to be turned on for approximately 30% more hours per year than if the building was fitted with 15% rooflights.

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Mar/Apr 2017

It’s important to note that the savings will only be made if the lights are switched off during periods when they are not required and for this reason automatic lighting controls should always be specified as part of the project. Recent research carried out by Elmhurst Energy supports these figures and gives detailed savings in building running costs resulting from improving daylight levels and installing lighting controls in existing buildings. The results show savings in running costs of up to £5.92/m2/yr, and savings of CO2 emissions up to 28.7kg CO2/m2/ yr can be achieved, with results from industrial and retail buildings very consistent. Slightly lower savings were achieved in the rooflit areas of a school (savings in running costs of £2.92/m2/ yr, and savings of CO2 emissions of 14.7kg CO2/m2/yr) primarily because significant sections of the rooflit areas were also well lit by windows, reducing

“Correctly specified rooflights will provide an outstanding longterm returns on investment”

www.daylightingmag.co.uk

Profile for BB2B

DAYLIGHTING Magazine issue 3 March/April 2017  Daylighting magazine mar apr 2017:2  

The bi-monthly magazine for architectural specifiers and technicians, building contractors and anyone interested in the provision of natural...

DAYLIGHTING Magazine issue 3 March/April 2017  Daylighting magazine mar apr 2017:2  

The bi-monthly magazine for architectural specifiers and technicians, building contractors and anyone interested in the provision of natural...

Profile for bb2b