The LED has emerged in the 21st century as the dominant light-source technology, largely supplanting the traditional incandescent technologies that illuminated buildings throughout the previous century.
Originally, the appeal of LED lighting systems rested largely on their long operating lifetime and their high efficacy. Improvements to LED technology and LED packaged devices are continuing to extend these benefits, but now the lighting industry is turning its attention to other parameters of the performance of LED lighting schemes, and in particular the quality of the light that they produce.
For instance, many LED lighting companies have introduced or are developing products for Human Centric Lighting (HCL) systems. This Design Note explains what is meant by HCL, and the reasons for its adoption in commercial and industrial lighting applications.
Biological effect of lighting
Unnoticed by most people in everyday life, the biological impact of lighting on human health and behaviour is profound. This impact is the result of the evolution of the human species. Our biological functions and processes are mainly based on our roots in equatorial Africa: because of this, our bodies operate on a constant rhythm of 12 hours of day and 12 hours of night. Human biology has only partially adapted to life in other parts of the world in which the length of days and nights changes during the course of the year.
The human body is made to be active during the day and to regenerate during the night, when various natural repair processes take place. For people’s well-being, both phases are important. And the difference between the activity phase and the recovery phase has to be as clear as possible.
The aim of HCL is to align the operation of artificial lighting schemes with the human body clock, and to recognise the primitive response of the human body to light at different times of day.
In an HCL scheme, brightness is increased during the day, and light with a higher blue content will be used. The cells in the retina that regulate the body’s internal clock are sensitive to this blue content in the spectrum of visible light. A wide-area light distribution across the ceiling or the walls is important to create a sky of light, as shown in Figure 1.
In the evening, spot illumination with a low blue content and low intensity is better suited to the body in its night mode.
This different spectral content of light at different times of day is reflected in the preferred colour temperatures: in the morning, colour temperatures of 5,300K or 6,000K mimic the activating impact of bright morning sunlight. During the day, it makes sense to continue to use lights with a cool colour temperature for long periods of time. Towards evening, these values should be reduced to below 3,000K.
Scientific studies have verified the positive effects of HCL on health and well-being. Long-term tests in schools, for example, have demonstrated that the rate of errors is reduced and that concentration and sustained attention are significantly improved. These factors are, of course, also important for office work. HCL could make office staff more productive, less prone to make mistakes and be absent from work through sickness less frequently.
Light management systems enable HCL and other functions
HCL is part of a wider trend in the lighting industry to provide more sophisticated, building-wide control of lighting schemes, in contrast to the traditional method of lighting control performed with a local on/off switch for every stand-alone luminaire.
In large-scale lighting industrial and commercial lighting installations, there is scope to save money by applying motion- and presence-detection systems, and by implementing special features such as the Constant Lumen Output (CLO) function. CLO is a feature of many of the OPTOTRONIC® LED drivers produced by OSRAM.
The use of intelligent control systems enables the user to flexibly group and address individual luminaires, clusters of luminaires or entire areas via light-management or building-management systems, as shown in Figure 2. Separate sites may even be connected and controlled remotely, a capability of the OSRAM ENCELIUM system.
The development of HCL technologies and sophisticated light management systems means that more and more installations in future will use dimmable instead of switchable lighting solutions. More widely, the implementation of LED technology is making everything connected with lighting equipment more intelligent.
OSRAM therefore expects to see increased use of LED driver data, such as information on energy consumption, dimming levels and remaining lifetime. These data can be used to optimise energy efficiency, for predictive planning and to streamline lighting maintenance operations.