Merlet College © Arjen Schmitz

While daylight does need to be supplemented by ample, high quality artificial lighting when outside light levels are low, where possible we should aim to make daylight the main source of lighting in schools

‘luminance ratio’ between visual task and near surroundings is a 1:10 within the field of view. (This ratio is an expression of the ratio between the luminance within the central vision and the peripheral vision of the surroundings.)

Glare caused by daylight differs from glare caused by electric light sources in terms of the size, complex luminance distribution, and acceptance of the users (e.g. people tend to be more tolerant of glare in a daylit environment).

The orientation of the windows can help control glare and contrast. Larger expanses of glazing could face north, allowing diffused daylight to penetrate throughout the day/year. The installation of opaque blinds can help to control daylight levels, as can permanent external shading.

Facade windows vs roof windows

Good daylight distribution across a room is best achieved by using several different daylight sources, like a combination of skylights and roof windows. For spaces where glazing will not allow enough daylight to penetrate, or where installation is not possible – such as large classrooms, lecture theatres or areas in the centre of a building – skylights are a great alternative. Operable skylights, strategically located, allow plenty of daylight during winter months, and provide fresh air year-round, improving indoor air quality and helping regulate temperature.

WWW.ARCHITECTSDATAFILE.CO.UK Building standards & light levels

Daylight performance in an interior space depends largely on the availability and properties of daylight at the building’s location (i.e. the prevailing climatic conditions). The proposed European Daylight Standard (FprEN 17037) suggests changing the basis of daylight evaluations to ‘daylight factor targets’ based on the occurrence of outdoor illuminance levels from recorded climatic data. The ‘climate connectivity’ of the proposal states that a space should achieve a target daylight level at work-plane height across a specified percentage of the relevant floor area for half of the daylight hours in the year. The target daylight level is based on interior illuminance higher or equal to 300 lux, corresponding to the requirement for lighting at workplaces.

The absolute light levels that are needed for a particular visual task will depend on the character of the task and the visual environment where it is performed. European Standard EN 12464-1: ‘Light and lighting – Lighting of work places – Part 1: Indoor work places’ provides information on the indoor light levels applicable for a school environment. Generally, the following interior light levels are recommended: • 100 lux where visual tasks are limited to movement and casual perception, e.g. circulation areas, corridors, etc

• 300 lux where visual tasks are fairly simple, e.g. classrooms, tutorial rooms, computer practice rooms. This should be the general minimum for all areas of school classrooms

• 500 lux where visual tasks are moderately difficult, and where colour judgment may be required, e.g. auditoriums, lecture halls, practical rooms and laboratories, libraries (reading areas), etc. In classrooms, this should be the level of light on the blackboard/whiteboard

• 750-1,000 lux where visual tasks are very difficult, requiring small details to be perceived.

Jens Christoffersen is senior researcher at Velux Daylight, Energy and Indoor Climate Centre

ADF MAY 2019

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