Licht & Displays – Adaptive Lighting

The right lighting can improve health and productivity. Intelligent light management technology and new light sources ensure an optimal mix of daylight and artificial light.

The quality of a light source is conventionally measured in terms of its luminous efficiency and service life. Today, however, there's an increasing focus on the connection between light and health," says Reinhard Weitzel, head of light source research at Osram. As he explains, good lighting and the right color of light are both important for well-being. For example, a worker on a night shift needs a different quality of light than someone at home reading a book. Studies conducted by Austrian lighting expert Prof. Christian Bartenbach show that a badly lit workplace causes stress and harms productivity. "We tested around 1,600 people over the course of five years. Bad lighting reduces productivity by 30 %," he reports.

Today, artificial light makes up between 60 and 80 % of the lighting in office buildings. But according to Bartenbach, channeling daylight indoors could cut the need for artificial light to 20 %. Depending on the weather, artificial light would be used to supplement lighting and replicate natural light conditions during the course of the day. Experts agree that daylight is the best light for people. We are used to about 100,000 lux in summer sunlight and 20,000 lux on cloudy days (1 lux equals 1 lm/m²). Indoors, however, things don't have to be quite so bright. In Germany, the law stipulates a minimum of 500 lux for office work and 300 lux for rough machine work. "But that's not really enough," says Weitzel, who bases his conclusion on current studies by ergonomists.

Smart Networking. Today, many light sources are in use – mainly filament, fluorescent and high intensity discharge lamps. "All types of light have their virtues. What's been lacking, however, is the realization that they need to be combined and controlled in order to create optimal lighting. What we need is a new architecture of light," explains Weitzel. In the future, lighting systems should be able to adapt to people's individual requirements.

Intelligent management of light can be used to meet such needs. But this requires adjustable lamps and intelligent, electronic operating units – including all the components to control and regulate lighting – plus light and motion sensors. And of course all these elements must be networked. With this in mind, the European lighting industry has come up with DALI, meaning Digital Addressable Lighting Interface. The DALI standard can be used to connect the ballasts required to operate discharge lamps, for example. Ballasts play a vital role in light management, guaranteeing high switching stability with variable lamp operation. When fluorescent lamps are combined with motion detectors, it is crucial that they continue to be reliable even when switched on and off at frequent intervals. A ballast can be compared to a diesel engine's glow plug: It ensures the necessary warm start.

A lighting system equipped with DALI can switch on, switch off and dim individual light components or groups of components, and it can communicate with a high-level building management system. This not only means that switching can be centralized and status queries about failed lamps can be processed; it also makes possible the creation of an adaptive lighting system. If the natural light outdoors is very bright, the artificial light component can be automatically reduced. But when it is cloudy, or evening or winter, the level of artificial light is increased. Moreover, preprogrammed lighting moods for meetings or presentations can also be recreated at the push of a button. Yet intelligent light management is only half of the story. "In the future, lamps will need to be highly efficient and have a long service life, excellent color reproduction and flexible color temperature," forecasts Germany's Federal Ministry of Education and Research (BMBF) in a report on the "Optical Technologies of the 21st Century." While some light sources boast several of these qualities, none can as yet combine all of them. The ideal situation, though, would be to have one lamp capable of meeting every single need.

Built-in LEDs. And such a lamp is exactly what the experts at Osram are planning to create – a hybrid light source. "Fluorescent lamps are very efficient, but it's difficult to alter their color temperature. Our intention is to combine them with LEDs to add an extra blue or red component to the white light," explains Weitzel. One compact hybrid lamp could then continually alter the color of the light and thereby create a lighting mood corresponding to the natural changes in daylight during the course of a day.

But the high-performance LEDs required for such a product (see article LEDs) are not only expensive; they are also less efficient and have a shorter service life when operated at temperatures over 65 °C. The latter is a problem, since the LEDs would be used inside fluorescent lamps, where temperatures can reach 100 °C near the electrodes. Nevertheless, Osram researchers are sure such difficulties can be solved with suitable heat discharge measures and intelligent component positioning. Furthermore, they are developing technologies to make fluorescent lamps more efficient and less dependent on mercury. Indeed, the BMBF has given its approval to a research program designed to investigate exactly these goals. The project is to run for three years. By then the researchers hope they will be able to present the first lamp that can light up even the dreaiest of days.

Evdoxia Tsakiridou

Designing Light for Healthy Living

How does light affect the psyche?

Bartenbach: Humans are visual animals. 90 % of our perception is visual, and many autonomic processes are also controlled by light. Reflected light is especially important. When I work at my PC, I see not only the screen but also the desk, the walls of my office, the windows and the world outside. I need to take into account their brightness as well.

What kind of impact can bad lighting have?

Bartenbach: I'll give you a simple example: If you work at a PC near a window, the light is blinding. The difficulty in adjusting leads to a given level of mental strain. As a result, you'll notice certain stress symptoms like sweating and tension. You make mistakes, work slower and become tired more quickly. That's something we've noticed in all of our studies. For optimal comfort, the illuminated area must have the right dimensions, and you also need good shielding against the sun and glare. And other elements in the setting have to be right as well. The desk, for example, should be medium gray or wood-tone, and the ceiling, walls and floor mustn't be too light, in order to prevent any reflections from shiny surfaces.

What kinds of lighting are best at different times of the day?

Bartenbach: The light in the morning has the highest color temperature – it's slightly bluish. In the evenings, there's more red. The spectrum used in artificial lighting should take this into account. In the morning, it should pep you up – the best color for desk work is a bluish white. For the evening, on the other hand, I recommend a warm, low-intensity reddish light.

What kind of lighting technologies will we see in the next two decades?

Bartenbach: We'll see increased use of systems to channel sunlight underground – into subways, for example, or into courtyards, narrow streets and voluminous spaces in larger buildings. Similarly, the LED will play an increasingly important role in artificial lighting. It has a long service life, is very economical and can be used to regulate the brightness and even the spectral composition of lighting. This will make it possible to create new interior lighting moods as well as open up new areas of application. New light sources and innovative lighting systems are going to play a significant role in fulfilling society's growing demand for healthy living.

Interview: Evdoxia Tsakiridou