Christian Sommer received his diploma and Ph.D degrees both in the field of optics from the Institute of Theoretical Physics at Graz University of Technology, Austria, in 2002 and 2004, respectively. In the following he joined the Institute of Surface Technologies and Photonics of the JOANNEUM RESEARCH Forschungsges.mbH in Weiz, Austria. The main focus of his research activities are design and optical simulation of optical systems. Currently he is deputy head of the research group “Light and Optical Technologies” and head of the Research Studio Austria project “Green Photonics”.
Smart Design of Freeform Micro-Optical Elements for Thin Direct Lit-Luminaires
Light-emitting diode (LED) based lighting solutions offer many advantages with respect to conventional light sources. This includes their huge potential for energy saving, long lifetime, high reliability as well as their compact size. Especially the last-mentioned aspect favors new concepts for the design and integration of light points and luminaires.
In case of a direct-lit luminaire for general lighting applications the LEDs are separated by a certain distance, arranged in a regular array and illuminate an out-coupling surface which is placed in a certain height above the LED array. One important parameter for such set-ups in order to maintain a uniform luminance is the ratio between the distance of the individual LEDs and the thickness of the luminaire (distance to height ratio = DHR).
An enhancement of the DHR value by using additional optical elements like, e.g., freeform optics, is highly desirable because it allows a reduction of the number of LEDs needed (cost aspect) or a decrease of the thickness of the luminaire by maintaining the uniform luminance (design aspect). However, this approach can cause additional problems when using common freeform optics because of their usually larger size and cost intensive mastering and production processes.
Recently, we have discussed a smart design for an extremely flat direct-lit luminaire for general lighting applications with an enhanced DHR (> 3) ratio. The main advantage of this concept is the application of very thin optical freeform structures (< 50 µm) imprinted on a foil substrate, allowing cost effective mastering and production processes (using greyscale laser lithography and roll to roll fabrication). In this contribution we discuss the latest achievements in this regard. In particular, we discuss new design strategies for the shapes and the arrangements of the freeform micro-optical elements, which allow for a further improvement of the uniformity of the luminance.