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Interview
Lighting Design: “The Right Light at the Right Time”

Mathias Wambsganß is Professor of Lighting Design and Building Technology at the Rosenheim University of Applied Sciences, sits on the board of the German Lighting Technology Association (LiTG) and is a founding partner of 3lpi, a lighting design studio in Munich. For the past 15 years, he has been involved in energy monitoring under the auspices of the Federal Ministry of Economy, where he carves up buildings into “energy slices.” In this interview, Wambsganß talks about the use of carelessly selected lighting systems, missed savings potentials, and the absolute necessity of placing humans at the center of any design.

Lighting today is supposed to be as efficient as possible. At the same time, users want convenience. Can these requirements coexist?

Yes they can because highly efficient lighting means are now available. There is no longer the need to optimize a lighting system based solely on its energy consumption. In addition, energy consumption and its associated costs should always be considered relative to other costs. Personnel costs, for example, are a much larger line item in the corporate budget. Lighting an office costs, in the worst case scenario of low availability of natural light and long operating times, 8–10 euros per square meter per year. As a comparison, employers pay 5,000 euros and more per employee over the same time period measured according to the same space. Considered this way, we must absolutely stop measuring lighting solutions based primarily on their energy characteristics, and start placing a greater emphasis on lighting quality. Because ultimately, lighting exerts an enormous influence on the well-being of employees and their performance.

If the quality of the lighting is not used as the basis for designing a conventional lighting system for a commercial building, what is?

There are standards for lighting a workplace, which mandate certain thresholds be met, for example, 500 lux in an office. Many regard meeting these illumination levels as equivalent to lighting quality. However, lighting illuminance cannot actually be seen. It describes the amount of light which strikes a surface. The effect on the human eye, however, depends on the surface material.


In addition, this standard assumes an employee who is 20 years old. Someone who is 50, on the other hand, requires 50% more light to perform visual tasks at the same level of quality. Therefore, I begin by asking if “500 lux” is the correct design goal at all. In considering productivity and light's influences on health, it has become quite clear that we need more light for tasks at certain times. In an expert forum at the LiTG, we are discussing whether this standard is sustainable in its current form over the long term. In this case, defining a bandwidth of 500–1,000 lux would probably be a better solution.

But the Energy Saving Ordinance also includes specifications. Will your desire for “more light” potentially conflict with efficiency goals?

To a certain, but small extent, yes. However, you have to look at the total relationship and consider things from a different point of view. For example, the installed output versus what is actually used, since the energy balance sheet ultimately counts what was actually consumed.


In order to arrive at a good result, a two-fold process makes more sense in my opinion: first, we should ask which lighting conditions are most useful in the work situation. The significance of the person who will work in this space plays an important role. Then, we undertake the necessary measures to configure the most efficient lighting solution. In addition to selecting efficient products, questions should also be raised about how to control or regulate the light. Although it has been documented that installing somewhat more lighting output makes financial sense, the possible savings of a lighting management system are even greater.

The basis for selecting a specific lighting system is being driven less by costs. Instead, the guidelines issued by the legislature are granted more weight, and they have stated that the question involves employee health and productivity.

The key phrase here is “the right light at the right time.” This relates to the quantity of light, and, where it makes sense, to the spectrum used. This means that the type and means for controlling light must be further developed so that selecting the “right” type of illumination becomes just as important efficiency.