Design and evaluation of an LED-based light fixture

Abstract

Interior spaces, such as conference rooms, require multiple forms of lighting to meet different task needs. Linear fluorescent lamp fixtures commonly produce the general ambient light, and reflectorized halogen lamp fixtures produce the directional lighting. Current lighting practice uses multiple light source technologies and fixtures to achieve the required illumination for the various tasks. However, many light fixtures can create an unappealing architectural design, especially in a small space, and multiple light source technologies can cause maintenance difficulties. The ideal scenario would be to create one fixture with a single type of light source that could meet a variety of lighting needs. The size, potential energy savings, and reduced maintenance benefits of white light-emitting diodes (LEDs) make them attractive for use in general illumination applications. Therefore, the goal of this study was to investigate whether a light fixture could be designed with white LEDs to provide different beam distributions. A commercially available ray tracing package was utilized to model, analyze, and optimize light fixture concepts created using LEDs and light guides. The fixtures were optimized for light output distribution and efficiency. While a rectangular-shaped light guide with simple diffused reflective surfaces provided the necessary cosine beam distribution, a more sophisticated surface treatment was required on the light extracting surface of the light guide to create the batwing beam distributions. The surface finish structures were in the form of micro-prism arrays. By switching LED arrays on and off to different light guides, various light levels and distributions could be achieved for different occasions. Further analysis showed that, when used in a typical conference room set up the fixture produced acceptable uniformity over the surfaces. Although the system provided the necessary beam distributions, the system efficiency was quite low, only 48%. Most of the light loss occurred in creating the batwing distribution. The overall system efficiency must be greater than 80% for this type of a fixture to become a viable solution.