Outside light levels fluctuate every hour of every day. One day light levels could be just 4,000 lux, the next as high as 14,000 lux. The geographic location, time of year and atmospheric conditions such as cloud cover in the sky will play a big part in the light level that enters a building along with of course the orientation of the facade and combination of glazing and shading system employed.
Glare occurs when there is a higher luminance level in the field of vision than the surroundings. This can then affect the ability to successfully and comfortably carry out general tasks, including computer work and book reading.
The CIBSE (Chartered Institution of Building Services Engineers) code for lighting states that "for a general office (tasks such as computer work, writing, drawing) a recommended lux level is 500 lux".
Excessive light therefore must be controlled to bring it to acceptable levels for the tasks that are being carried out. There is of course also the desire to maintain a view and connection to the outside, an important factor in occupant well-being, hence the reason why buildings have windows in the first place.
Exterior blinds diffuse harsh light, spreading and evenly distributing incoming light to avoid the chances of glare. To what deree will depend on the light transmission value of the fabric along with openness factor - see related article 'The Openness Factor' for more information.
The BBSA (British Blind and Shutter Association) have put together recommended transmission of visible light (TV) figures for blind fabrics based on different applications:
Managing the varying daily light levels and controlling glare is often complex, yet an important consideration to make in ensuring good visual comfort. Hopefully this article and the above suggested guideline fabric light transmission figures will be of help.
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Glare is a difficult element to control
