Design and evaluation of inorganic and organic light-emitting diode displays for signage application




Sharma, Pratibha

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High brightness inorganic LEDs have been utilized effectively for signage application using the edgelighting technique. In this thesis. the inorganic LED-based edgelit signage using transparent acrylic has been evaluated. We determine that the edgelighting technique, although superior in efficiency to other available techniques, suffers from intrinsic limitations, particularly in terms of illumination uniformity. The illumination uniformity can be improved by external means such as a diamond grating. In order to quantitatively establish this, the illumination uniformity of the LED-based signage with and without the diamond grating is examined. The results show a considerable improvement in the illumination uniformity when a diamond grating is used. However, the high cost of the diamond grating and the transparent acrylic amplify the overall cost of signage using LEDs. Therefore, a distributed light source, which can eliminate the use of the diamond grating. is determined to be more suitable for signage application. Organic Light-Emitting diode (OLED), which is a distributed light source, emerges as a possible contender. The second part of our research focuses on the application of OLEDs for signage. We examine two OLED modules from different manufacturers for our evaluation. The first module is a prototype module obtained from the National Research Council (NRC) and the second module is a commercially available OLED from RiT Display Corporation. We present novel design techniques that can be used to implement signage based on OLEDs. A prototype tiled OLED display using commercially available OLEDs is designed and tested. Our investigation suggests that good light uniformity in signage panels can be achieved using OLED modules in the form of tiles. This proves that OLEDs are superior to conventional light-emitting diodes as light sources for signage in terms of illumination uniformity. However, we determine that the currently available OLEDs have a lower light-conversion efficiency in addition to higher costs when compared with conventional LEDs. Though the individual OLEDs cost more than LEDs. signage panels based on OLEDs can be made cheaper by avoiding the use of acrylic sheet and diamond grating. Moreover, the light weight of OLEDs and the fact that OLEDs are diffused sources (rather than point sources like LEDs) add an additional advantage. Also. OLEDs have the potential to be built inexpensively on flexible substrates by using the roll-to-roll technique. This makes OLEDs superior to conventional LEDs in large-area signage applications.



light emitting diodes, signs and signboards