Abstract
Advances in semiconductors have made available low-cost, easy-to-integrate sensors and controllers that are basic building blocks in intelligent lighting systems. Sensors provide information about the environment based on which a controller may adapt a certain lighting characteristic. In indoor lighting systems, occupancy and light sensors are typically used to control illumination based on occupancy state and daylight levels, respectively. For instance, if there is occupancy, the lighting system may be dimmed up to a level such that together with daylight, the total illuminance achieves a desired minimum illuminance value. Thus, by providing lighting when and in the right amount needed, system-level energy savings may be realised. Similarly, in outdoor lighting systems, dimming of lamps at light poles may be controlled based on presence and traffic conditions, as well as ambient light levels. In contrast to indoor lighting where occupant visual comfort is a design criterion, in outdoor applications safety is a primary concern when designing the control strategy.
Sensors thus provide the raw data on which intelligent processing is needed to extract information that is meaningful for a given lighting application. This sensing function thus provides a contextual translation of an environmental characteristic based on which a certain aspect of the lighting system may be adapted. The adaptation is performed by the control function provided via one or more lighting controllers. The sensing and control functions thus enable a new generation of lighting systems that are responsive to environment changes and user needs. For proper light adaptation, the sensors should foremost provide sensing information that is reliable and timely. For instance, an occupancy sensor should output the true occupancy state with minimal missed detections, false alarms and latency. Similarly, light sensor output should be indicative of the actual illuminance levels in its environment. The controller, on the other hand, has to be robust to sensor imperfections and errors that might be incurred, and also to information loss and delays in the case of a networked lighting control system.
Sensing information is currently provided by sensors that are part of a fixed infrastructure. With increased miniaturisation, improvements in battery/energy-harvesting technologies and wireless networking, plug-and-play sensors that can be easily integrated into different elements such as luminaires and objects in the environment will emerge. This will have a consequence on how lighting systems are controlled – moving from centralised to more distributed control methods. Specifically, having sensing and control functions at luminaire level will enable intelligent and modular light sources. Furthermore, as smart mobile devices become increasingly pervasive, more intuitive approaches to interaction with the lighting system will emerge, and sensing information will be made available in ways such that the user is an integral part of the control loop.
While new ways of sensing and control bring about a generation of intelligent lighting systems, a careful cost-benefit analysis is also required that will ultimately determine which intelligent lighting system architectures successfully evolve further.