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High-brightness, inorganic light-emitting diodes (LEDs) have been successfully utilized for edge-lighting of large
displays for signage. Further interest in solid-state lighting technology has been fueled with the emergence of small
molecule and polymer-based organic light-emitting diodes (OLEDs). In this paper, edgelit inorganic LED-based displays
and state-of-the-art OLED-based displays are evaluated on the basis of electrical and photometric measurements. The
reference size for a signage system is assumed to be 600 mm x 600mm based on the industrial usage. With the
availability of high power light-emitting diodes, it is possible to develop edgelit signage systems of the standard size.
These displays possess an efficacy of 18 lm/W. Although, these displays are environmentally friendly and efficient, they
suffer from some inherent limitations. Homogeneity of displays, which is a prime requirement for illuminated signs, is
not accomplished. A standard deviation of 3.12 lux is observed between the illuminance values on the surface of the
display. In order to distribute light effectively, reflective gratings are employed. Reflective gratings aid in reducing the problem but fail to eliminate it. In addition, the overall cost of signage is increased by 50% with the use of these
additional components.
This problem can be overcome by the use of a distributed source of light. Hence, the organic-LEDs are considered as a
possible contender. In this paper, we experimentally determine the feasibility of using OLEDs for signage applications
and compare their performance with inorganic LEDs. Passive matrix, small-molecule based, commercially available
OLEDs is used. Design techniques for implementation of displays using organic LEDs are also discussed. It is
determined that tiled displays based on organic LEDs possess better uniformity than the inorganic LED-based displays.
However, the currently available OLEDs have lower light-conversion efficiency and higher costs than the conventional,
inorganic LEDs. But, signage panels based on OLEDs can be made cheaper by avoiding the use of acrylic sheet and
reflective gratings. Moreover, the distributed light output and light weight of OLEDs and the potential to be built
inexpensively on flexible substrates can make OLEDs more beneficial for future signage applications than the inorganic
LEDs.
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