Studies in ambient intelligent lighting

The revolution in lighting we are arguably experiencing is led by technical developments in the area of solid state lighting technology. The improved lifetime, efficiency and environmentally friendly raw materials make LEDs the main contender for the light source of the future. The core of the change is, however, not in the basic technology, but in the way users interact with it and the way the quality of the produced effect on the environment is judged. With the new found freedom the users can switch their focus from the confines of the technology to the expression of their needs, regardless of the details of the lighting system. Identifying the user needs, creating an effective language to communicate them to the system, and translating them to control signals that fulfill them, as well as defining the means to measure the quality of the produced result are the topic of study of a new multidisciplinary area of study, Ambient Intelligent Lighting. This thesis describes a series of studies in the field of Ambient Intelligent Lighting, divided in two parts. The first part of the thesis demonstrates how, by adopting a user centric design philosophy, the traditional control paradigms can be superseded by novel, so-called effect driven controls. Chapter 3 describes an algorithm that, using statistical methods and image processing, generates a set of colors based on a term or set of terms. The algorithm uses Internet image search engines (Google Images, Flickr) to acquire a set of images that represent a term and subsequently extracts representative colors from the set. Additionally, an estimate of the quality of the extracted set of colors is computed. Based on the algorithm, a system that automatically enriches music with lyrics based images and lighting was built and is described. Chapter 4 proposes a novel effect driven control algorithm, enabling users easy, natural and system agnostic means to create a spatial light distribution. By using an emerging technology, visible light communication, and an intuitive effect definition, a real time interactive light design system was developed. Usability studies on a virtual prototype of the system demonstrated the perceived ease of use and increased efficiency of an effect driven approach. In chapter 5, using stochastic models, natural temporal light transitions are modeled and reproduced. Based on an example video of a natural light effect, a Markov model of the transitions between colors of a single light source representing the effect is learned. The model is a compact, easy to reproduce, and as the user studies show, recognizable representation of the original light effect. The second part of the thesis studies the perceived quality of one of the unique capabilities of LEDs, chromatic temporal transitions. Using psychophysical methods, existing spatial models of human color vision were found to be unsuitable for predicting the visibility of temporal artifacts caused by the digital controls. The chapters in this part demonstrate new perceptual effects and make the first steps towards building a temporal model of human color vision. In chapter 6 the perception of smoothness of digital light transitions is studied. The studies presented demonstrate the dependence of the visibility of digital steps in a temporal transition on the frequency of change, chromaticity, intensity and direction of change of the transition. Furthermore, a clear link between the visibility of digital steps and flicker visibility is demonstrated. Finally, a new, exponential law for the dependence of the threshold speed of smooth transitions on the changing frequency is hypothesized and proven in subsequent experiments. Chapter 7 studies the discrimination and preference of different color transitions between two colors. Due to memory effects, the discrimination threshold for complete transitions was shown to be larger than the discrimination threshold for two single colors. Two linear transitions in different color spaces were shown to be significantly preferred over a set of other, curved, transitions. Chapter 8 studies chromatic and achromatic flicker visibility in the periphery. A complex change of both the absolute visibility thresholds for different frequencies, as well as the critical flicker frequency is observed. Finally, an increase in the absolute visibility thresholds caused by an addition of a mental task in central vision is demonstrated