On the basis of three examples, luminance values are compared with each other in specific applications. The examples are the square in front of a historical function building, a train station concourse and a shop for exclusive accessories in a pedestrian zone. In the description of the illumination, we shall proceed from the lowest luminance and define this as “1”. All other values are calculated according to this, to illustrate the ratios between the luminance values.
The examples listed above show possible luminance distributions. From the darkest area to the brightest area, some of the differences are extreme. Accordingly, the light is felt to be pleasant. Why?
Square in front of a historical function building
In the function building (example 1), the entrance represents the brightest point. The luminance increases gradually for the visitors as they arrive. The entire situation can be grasped at a glance. These factors convey a feeling of safety. The spatial situation is clear, and is given a clear structure through light. The path towards the event is shown through the increase in luminance. Visitors can easily find their way around, and get the feeling that they are in good hands.
Train station building
In the station (example 2) soft transitions between the various luminance levels are important. Many travellers are in a hurry. The focus is on information about train connections. Highly contrasting lighting conditions would interfere. Here, a build-up of tension in the illumination has largely been dispensed with. Certain zones are emphasised slightly, by increasing the luminance values at the information desk and in the shop passages. All in all, the light in the station is uniform and conveys a feeling of visual tranquillity. The eye hardly has to adapt.
Shop with exclusive accessories in a pedestrian zone
The illumination in the exclusive shop (example 3), on the other hand, is tense and accentuated. High contrasts attract the attention directly to the presentation of the goods. Despite these differences in light intensity, customers find that the light is pleasant. Here too, the entire situation can be grasped quickly.
Very strong light-dark contrasts appear within the human field of vision. Apparently these contrasts are added up to form an average value, for they do not cause the eyes to tire rapidly. If the eyes were exposed to such strong alternating contrasts, their adjustment work would be enormous. If a lighting situation can be grasped at a glance, therefore, sharp differences in luminance distribution can be used meaningfully. In this way, an arc of tension can be built up with light and persons can be guided and accompanied.
If a room is uniformly illuminated with a certain luminance and the dimensions of this room completely fill the human field of vision, the transition to a more strongly or less strongly illuminated area should only be gradual. In this way, the eye has a good chance to adjust to the change in lighting conditions without becoming tired. Here, jumps between greatly differing luminance levels would lead to glare and rapid fatigue. Good illumination makes a significant contribution to our well-being and often leads to business success. In the end, the light designer must decide on site which light is the best in the situation in question.