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More (day-)light

Thoughts on the new daylight standard EN 17037

Even though Goethe, depending on the source, demanded a chamber pot at his deathbed or he simply complained about an uncomfortable couch [„Mer lischt (hier so schlächt)“, which means: „One is lying here so badly“], the desire for “more light” is probably the poet’s best-known quote. 

This desire was taken up by the technical committee "CEN/TC 169" and after many years of work it presented with the EN 17037 the first Europe-wide standard on "Daylight of Buildings". Since the beginning of the year, this standard has now been in force throughout Europe, replacing various national standards or closing the gap where no standards existed until now. 

What does this new standard regulate?

The EN 17037 gives recommendations on the daylighting of buildings, distinguishing between three quality levels (minimum, medium, high). Four essential aspects are addressed, for the middle level it is required:

  • Sufficient daylight provision in rooms. For example, for vertical daylight openings 500lx on 50% of the area and 300lx on 95% of the area must be given for over 50% of the annual daylight hours.
  • In order to connect to the outside world and to provide users in the room with information about the environment, geometric specifications for daylight openings and thus for the view are defined. For a medium rated view, an external visibility of more than 20m (for example, the distance to the external facade of the neighboring building) and a horizontal viewing angle of at least 28° must be demonstrated. In addition to the landscape level, another level - either sky or ground - must be visible from at least 75% of the used area.
  • The quality criterion of the exposure to sunlight is determined for patient rooms, playrooms and living rooms. The sunlight exposure duration at a reference point on the inner surface of the daylight opening on a selected date between the 1st of February and the 21st of March should be at least 3 hours.
  • Anti-glare devices should be used for all rooms with daylight openings. In particular, the glare protection is to be evaluated for rooms in which activities such as reading, writing or the use of display devices take place. A Daylight Glare Probability (DGP) value of 0.40 may be exceeded by a maximum of 5% of the annual usage of the room.

As you can see, this is very complicated, and can probably only be demonstrated by experts with complex annual simulations. And what is also noticeable: the daylight factor (DF) is possibly on the long-term obsolete (even if a "back door" was left open in the form of a simplified and technically questionable DF-method).

And what effects does the new standard have on daylight design?

The recommendations clearly show two things: On the one hand, the new standard EN 17037 is an extremely complex set of rules requiring a correspondingly profound occupation and interpretation. On the other hand, the defined goals are sometimes extremely ambitious. For example, so far, the German standard DIN 5034 used a daylight factor of 0.9% (that the space is considered as daylit) or 2% (for sufficient daylighting). According to the new standard, the comparable value for Germany is now 2.2% (recommendation level minimum), 3.6% (medium) or 5.4% (high). At the same time, the regulations pose new challenges for the lighting designer, because hardly any commercial software provides evaluations for all the requirements.

However, the new standard has in any case one extremely positive side effect. The discussion about daylighting of buildings is likely to be conducted more intensively among lighting designers, architects and building owners, and a critical examination of the subject is carried out. 

Bartenbach has also attended to the new standard. For example, in-house software packages have been extended in order to carry out all evaluations according to the EN 17037. At the same time, these required values confirm Bartenbach's high demands on the daylighting of buildings. Only in this way a user-centered lighting design can take place, which in the end leads to improved health and visual comfort in buildings.

In this sense, Goethe's quote probably includes both: the call for a more extensive use of daylight to achieve biological lighting effects and visual comfort, as well as the desire for a more intense engagement with the topic itself: "More (day-)light!" .

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