Daylight is essential for human beings. However, we spend 90% of our time is spent in rooms indoors. Some of these rooms are insufficiently supplied with daylight. The provision of daylight leads to more than just being able to see well: We are becoming ever more aware of the impact of daylight on general well-being. Good amounts of daylight can have a positive effect on mood, performance and even health. Daylight also contributes significantly to energy contributes significantly to energy consumption in terms of electric lighting.
For the first time, in the new European standard EN 17037 “Daylight in Buildings”, which will shortly be available in Germany as DIN EN 17037 “Tageslicht in Gebäuden”, there are recommendations applicable Europe-wide regarding the provision of daylight and its quality.
DIN EN 17037 means a change to the current state of the art. It should therefore be closely taken into account by planners and contracting entities.
Not all of the content of the national standard series DIN 5034 “Daylight in interiors” is covered by DIN EN 17037. For this reason, the individual parts of DIN 5034 are currently under review and, if necessary, will be adapted to DIN EN 17037, or supplemented and updated.
DIN EN 17037 is applicable to all rooms used for longer periods of time and on a regular basis. Rooms which require an absence of daylight are excepted from this standard. The technical rules for workplaces applicable in Germany, e.g. ASR A 3.4, are unaffected by this. DIN EN 17037 gives recommendations on three levels regarding the basic provision of daylight for illuminating interiors, regarding the quantity of hours of sunlight, the visual connection to the outside, as well as the evaluation and limitation of glare (see attachments).
The recommended levels can be used during the planning and calculation stages, but also for checking daylight conditions. Because currently there is no room use allocated to the respective recommendation levels, it is possible for those involved in the construction to reach an agreement on the daylight requirements, depending on the property in question.
So as to describe the new paths and recommendations of DIN EN 17037 in more detail, and to provide some initial proposals on the application of the different levels, national standardisation bodies are currently writing an application paper regarding the introduction of DIN EN 17037 and another paper on the distinction with regard to the valid DIN 5034.
Brief overview of the essential content of EN 17037
The European standard EN 17037 “Daylight of Buildings”, which is to be incorporated in Germany as DIN EN 17037 “Tageslicht in Gebäuden”, in part introduces new criteria, approaches to evaluation and recommendations regarding daylight, the view, exposure to sunlight and glare from daylight:
1. Provision of daylight
For many years, the influence of daylight on a building's energy requirements has been classified under the concept of relative exposure to light – “daylight autonomy”. EN 17037, under the term “Daylight supply”, now also incorporates into the evaluation the availability of daylight over time. A room is deemed to be sufficiently supplied with daylight, according to EN 17037, if a target level of illuminance is achieved over a specified portion of a reference plane, for at least half of the daylight hours. This corresponds to a relative exposure to light (“daylight autonomy”) of 50%. This can be substantiated either via a detailed simulation using validated software – on which the approaches in energy standards are also based – or using a simplified procedure as specified in EN 17037, based on the daylight ratio.
With the simplified method of substantiation, minimum daylight ratios are given – dependent on the geographical location and the climate –, whereby the assumption here is the illumination is diffuse and comes from the sky, and that only glass is used in the facade openings. This is to ensure that the desired illuminance values, e.g. 300 lx, can be achieved through daylight alone over a minimum period, i.e. 50% of the daylight hours, and over a minimum of 50% of the usable space (see Figure 1). For vertical facades, a target daylight factor of 2.2% applies in Germany for a desired illuminance of 300 lux (D300), 3.6% for 500 lx (D500) and 5.4% for 750 lx (D750). For roof skylights, the analogous values are 1.8 % (D300), 2.9 % (D500) and 4.4 % (D750). The previous minimum value of 0.9% for rooms with vertical facades (from DIN 5034) is not taken into consideration in the new standard. With regard to the facade parameters, in the simplified model for EN 17037, the “daylight supply” depends solely on the transmittance value of the glazing. The structure of the sun and glare protection is not taken into account.
In terms of the simulated observer positions in the building, the views may in future be classified as a function of a horizontal viewing angle, an exterior line of sight and the nature of the visible environment (“no-skyline, no-ground-line concept”) – with the recommendation levels “Minimum, Medium, High”. (see Figure 2).
The horizontal viewing angle and the exterior line of sight are the evaluation criteria in this respect; and they depend on the size and positioning of the facade. A large surface area of window generally has a positive impact on the evaluation.
3. Exposure to sunlight
Minimum recommendations for sunlight exposure are given for rooms. The reference points to be taken into account are window-related. The evaluation itself is independent of the actual size of the window(s).
4. Protection against glare from daylight
For rooms reading or writing is done, or devices with a display used, it is recommended that shading is deployed. The Daylight Glare Probability (DGP) is used to assess the anti-glare effect. The procedure primarily concerns sun/anti-glare protection. In terms of glazing, only “glazing with low transmission” or “electrochromic glazing” may be evaluated, whereby they must demonstrate very low light-transmission values when switched on. It is assumed that glazing with a higher light-transmission value has insufficient glare protection.
Graphics: Fraunhofer-Institut für Bauphysik IBP, Stuttgart IBP
The Deutsche Lichttechnische Gesellschaft e.V. (LiTG) is headquartered in Berlin, and is a registered independent association with over 100 years of history and around 2300 members. LiTG is a dynamic network and knowledge platform for all those interested in light. It deals with “light and lighting” in the areas of technology, design, planning and application in theory, practice and research – at regional, national and international levels. It gives advice to interested parties. It has a wide-ranging programme of events. It is involved in the development of national and international standards and cooperates with relevant professional bodies, such as DIN, CEN and CIE, as well as with national lighting bodies. Since 2015, it has run a training programme for “Certified Lighting Experts (LiTG)”, based on the European training standard “European Lighting Expert (ELE)”. Since June 2016, it has been a partner in the INTERREG Central Europe CE452 “Dynamic Light” programme. It authors and distributes the results of work and research in the form of scientific publications.