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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.

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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.

Matthias Wambsganß

Professor of Lighting Design and Building Technology

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.

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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.

Mathias Wambsganß

Professor of Lighting Design and Building Technology

How should this look in your opinion?

If you consider how sensitively and directly our eyes react, then it is actually quite difficult to control or regulate lighting. In my opinion, this has yet to be sufficiently described. Therefore, we need information on how to best bring the technical specifications into harmony with the ergonomics of the human eye. An example: If an office is equipped with daylight-dependent lighting control, then the brightness should not start up directly at 100% and then drop to the setpoint. The user has the feeling that it is too dark, because the human eye adjusts quickly to higher light levels, but takes longer to adapt to reduced light. The message to the user is inevitably that he or she could have more light, but is not getting it. Conversely, the lighting amount should not slowly switch on, rising gradually in the direction of the nominal illumination – the user will quickly assume that there are problems with the light switch. In order to set such points correctly in the controller, the programmer needs to know what the suitable values are for each function, and which system characteristics are expected by the user upon start up.

Is the current procedure for the acceptance of lighting systems thus not mature enough because the electrical engineers do not know enough about the specifics of visual ergonomics?

To a certain extent, yes. Many experts are not yet aware of this. In general, they don't know how the eye functions, and thus cannot adequately consider the relevant factors during operation or acceptance. From this, we should derive that it is actually logical to work toward a better method for operation and acceptance of lighting systems. This does not have to be a standard established by the legislature. It could, for example, also be based on information from the manufacturers of lighting controllers regarding how a system with their components functions most ergonomically in specific applications. The knowledge that we already have only helps the operator if someone has applied this information to improve things. That is, we need guidelines to enact best practices.

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From this, we should derive that it is actually logical to work toward a better method for operation and acceptance of lighting systems.

Matthias Wambsganß

Professor of Lighting Design and Building Technology

Do you assume then, that your stated claim of promoting lighting quality through lighting control will shape sensor design and technology?

That could become necessary, since currently available sensors generally only measure brightness in addition to presence. If you look at the topic of “Lighting and Health”, sensors are necessary for evaluating the light received by the non-visual function of the eye, or measuring the spectral composition of the light. Prof. Herbert Plischke, endowed chair for “Lighting and Health” at the University of Munich, is currently experimenting with sensors that will contribute to this. However, I assume that it will take a few large-scale applications to make such sensors affordable.

Do you believe that a system that functions well differs from an investment standpoint, from a system that does not operate as well? The use of technology is often quite similar...

There is certainly no difference from the hardware side. I have seen lighting solutions with expensive hardware that did not function, or only had limited functionality. Hardware can obviously be a source of errors, for example, if a sensor was selected with features that don't fit the installation location. However, if I assume that designers sought the correct components, then the question becomes whether a greater expense is incurred during properly executed commissioning, i.e, if it was properly dimensioned and parameterized. In which case, I believe yes. However, I believe that this expense should be paid. If the design's challenges are properly documented, then they should not be classified as “extra” costs by building owners.

Can you count on savings during operation if the commissioning has been carefully executed?

Not necessarily. However, you will spare yourself aggravation on the part of your users – and that is almost priceless. If a carelessly commissioned system leads to controls that are virtually inoperable, then there are naturally increased operating costs. The potential savings are lost.

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You will spare yourself aggravation on the part of your users – and that is almost priceless.

Matthias Wambsganß

Professor of Lighting Design and Building Technology

Requirements from the Energy Savings Ordinance also apply to existing buildings. In your opinion, are the savings potentials of lighting large enough to budget for during renovations?

Naturally, this depends on the age of the current system and how radical the renovations are. However, even asking the simple question, “how much light per watt used actually reaches the space,” leads quickly to a positive result. If you compare modern, LED-based lights with conventional fluorescent tubes from 15 years ago, they are separated by a factor close to two. Merely changing the lights can be seen as “picking the low-hanging fruit.” Automating the system is another option that provides additional savings potential.

What challenges do you see most often in renovation projects?

In a core renovation, that is, when new cabling is laid, it functions like new construction for designers. A partial renovation is quite different. If the ceiling lighting points are maintained – that is, there is only one available power supply line – then there are large restrictions on solutions that extend significantly past pure analog on and off switches. In the future, that would be a point to recommend wireless solutions.

Imagine that you were the operator and could decide which system would be installed. Do you see an advantage if your own personnel were in a position of replacing defective components or adapting the system when the spaces are restructured?

Aren't a lot of systems essentially proprietary because they bear the hallmarks of the programmer? Even when selecting an open-source system, a certain level of dependency is generated during commissioning. Against this background, what you are describing seems almost like a dream. It would have to occur like this: in case I convert the space, I could assign the lights and switches with my own personnel and wouldn't need a highly trained and expensive programmer. As an operator, I would certainly not be happy with a forced marriage to my system programmer.

Interview: Martin Hardenfels and Julia Ockenga

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