Mohamed Boubekri
Daylighting Modern libraries are places for learning as well as entertainment. Libraries demand sophisticated lighting systems that are of high visual comfort and flexible enough to respond to the numerous visual tasks taking place in libraries. The daylighting of libraries has some unique physiological requirements that differ from many other building types. The requirements relate to the quantitative and the qualitative aspects of visual performance defined by illuminance levels, distribution of light, glare and visual comfort. Lighting in libraries is important because of many reasons. Sufficient light levels must be provided for the users to be able to write on horizontal and read on vertical surfaces such as bookshelves. Design consideration may include avoidance of all forms of glare, excessive sunlight penetration and too high or too low contrasts. The dynamic character of daylight must be taken into account in order to maintain the quantitative and qualitative aspects of illumination.
General Lighting Requirement for Libraries Illuminance Levels The goal of lighting in libraries is to facilitate the learning experience by providing adequate and comfortable light levels that can be endured for prolonged periods of time. The main visual tasks in libraries are reading and writing texts, differing in size, shapes and contrast levels. Reading tasks may vary from children’s books printed in 10- to 14-point type on matte paper to newspapers printed in 7-point type fonts. Other tasks, such as studying illustrations and handwritten pages varying in contrasts are possible. An illuminance level of 300–500 lux is recommended for reading rooms.1 Both the stacks areas and the general reading areas require toplighting. The stacks need toplighting because the book shelves block light coming from the sides. For the general reading area it is also recommended to have uniform lighting in order to allow for flexibility of use of the space. Light Uniformity Uniform light is the most widely used form of illumination in libraries. Such a strategy provides ideally the same illuminance level for the entire workplane where a specific visual task is performed. In practice this is not always possible and, inevitably, there is always variation in illuminance levels on the same workplane and between workplanes. To address this issue of light level variations, lighting standards in several countries prescribe maximum uniformity ratios (ill. 1), ratios between lowest light levels to average light levels in the room that should not be exceeded.2 Source document
Uniformity ratio across task area
CIBSE Code for Interior Lighting
0.8 minimum/average
Deutsches Institut für Normung. DIN 5035 Innenraumbeleuchtung mit künstlichem Licht (1979)
0.67 minimum/average
Standards Association of Australia. AS 1680 Code of Practice for Interior Lighting (1976)
0.67 minimum/average
Nederlandse Stichting voor Verlichtingskunde Aanbevelingen voor Binnenverlichting (1981)
0.7 minimum/maximum
CIE Guide on Interior Lighting (1986)
0.8 minimum/average
1 Recommendations for illuminance uniformity
While it is impossible to obtain uniform illumination through side windows, it may be possible to obtain more uniformly distributed natural light using a number of top daylighting strategies. Due to the dynamic quality of daylight, light levels are cons tantly changing according to the time of day and seasons. As a result, the distribution may be uniform but the daylight levels are never constant throughout the day.
90 TECHNICAL REQUIREMENTS