ABSTRACT
The concept of "television on the wall has become a reality. Recent breakthroughs in LCD and PDP technologies yielded 42", 50", 60" and above diagonal models. Can these technologies evolve in order to obtain a larger than 150", direct view and slim "wall TV"
(SWTV)? A new approach utilizing carbon field emission elements as the building blocks for SWTV is presented and discussed.
INTRODUCTION
Today's display industry demonstrates trends toward polarity, with manufacturers at one end cultivating large screens and better definition than ever before. On the other hand, development efforts are continuously enhancing thin, lightweight, low power consumption displays for use in mobile equipment.
Furthermore, although CRTs remain the main stream display format and the standard by which all other display are measured, other electronic display technologies are attracting strong attention. These electronic displays encompass LCDs, PDPs, VFDs, EL and LEDs.(1),(2) Each serves in a different market sector or niche, depending on the screen size, the pixel count and the panel configuration.
Figure 1 shows the target applications for the different technologies as function of the number of pixels and diagonal size. As we can see, a large technological gap exists between 80" diagonal displays and over 150" diagonal displays. Interesting to note, that due to the growing markets for outdoor digital large displays, presently a number of technologies coexist and compete for these applications.
Figure 1. Target applications for the different technologies as function of the number of pixels and diagonal size.
Electronic sign boards, that must be very bright, generally use VFDs, LEDs or gas discharge devices (see comparison in figure 2). For the purpose of obtaining large area displays one can start from the existing monolithic type displays with the diagonal of less than 30" and expect that eventually these technologies will expand in order to obtain SWTVs. Alternatively one can start from the existing outdoor large area display
technologies and improve the resolution and the picture quality in order to obtain the same result.
LARGE AREA OUTDOOR DISPLAYS, COMPARISON OF BENEFITS
Figure 2 presents a comparison of extremely bright display technologies for large electronic outdoor screens.(3) VFDs and gas discharge devices possess large areas of illumination and therefore usually are superior to LEDs in picture
Figure 2. Comparison of extremely bright
displays for large electronic screens
quality. LEDs offer a limited area of illumination. This becomes a drawback in panels that use large pixel pitches. Under these conditions an LED needs to offer greater brightness per area than other devices. Panels that use such LEDs illustrate this disadvantage clearly. The display seems to glitter or twinkle at the illumination point resulting in poor picture quality. Furthermore, most LEDs use frontal lenses to improve the brightness. However, these lenses decrease the viewing angle. Meanwhile, gas discharge devices offer poor contrast because the discharge phenomenon
prevents the devices from turning off completely. Also, the discharge phenomenon is unstable at temperatures below freezing.
In contrast to LEDs, VFDs offer better luminous efficiency using 30% less power than other devices. For these reasons in the past companies such as Sony chose the picture element tubes based on VFD technology (PET VFD) which offers an extremely bright color picture element plus stable operation and excellent picture quality (see figure 3).
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