An LED display is a video display which uses light-emitting diodes. An LED panel is a small display, or a component of a larger display. They are typically used outdoors in store signs and billboards, and in recent years have also become commonly used in destination signs on public transport vehicles. LED panels are sometimes used as form of lighting, for the purpose of general illumination, task lighting, or even stage lighting rather than display.
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Types
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There are two types of LED panels: conventional, using discrete LEDs, and surface-mounted device (SMD) panels. Most outdoor screens and some indoor screens are built around discrete LEDs, also known as individually mounted LEDs. A cluster of red, green, and blue diodes is driven together to form a full-color pixel, usually square in shape. These pixels are spaced evenly apart and are measured from center to center for absolute pixel resolution. The largest LED display in the world is over 1,500 foot (457.2 m) long and is located in Las Vegas, Nevada covering the Fremont Street Experience. The largest LED television in the world, the Center Hung Video Display at Cowboys Stadium, is 160 by 72 feet (49 by 22 m), 11,520-square-foot (1,070 m2).
Most indoor screens on the market are built using SMD technology—a trend that is now extending to the outdoor market. An SMD pixel consists of red, green, and blue diodes mounted on a chipset, which is then mounted on the driver PC board. The individual diodes are smaller than a pinhead and are set very close together. The difference is that the maximum viewing distance is reduced by 25% from the discrete diode screen with the same resolution.
Indoor use generally requires a screen that is based on SMD technology and has a minimum brightness of 600 candelas per square meter (cd/m², sometimes informally called nits). This will usually be more than sufficient for corporate and retail applications, but under high ambient-brightness conditions, higher brightness may be required for visibility. Fashion and auto shows are two examples of high-brightness stage lighting that may require higher LED brightness. Conversely, when a screen may appear in a shot on a television studio set, the requirement will often be for lower brightness levels with lower color temperatures (common displays have a white point of 6500 to 9000 K, which is much bluer than the common lighting on a television production set).
For outdoor use, at least 2,000 cd/m² is required for most situations, whereas higher-brightness types of up to 5,000 cd/m² cope even better with direct sunlight on the screen. (The brightness of LED panels can be reduced from the designed maximum, if required.)
Suitable locations for large display panels are identified by factors such as line of sight, local authority planning requirements (if the installation is to become semi-permanent), vehicular access (trucks carrying the screen, truck-mounted screens, or cranes), cable runs for power and video (accounting for both distance and health and safety requirements), power, suitability of the ground for the location of the screen (if there are no pipes, shallow drains, caves, or tunnels that may not be able to support heavy loads), and overhead obstructions.
Flat Panel LED Television Display
History - possibly the first true all LED flat panel television screen was developed and documented by J. P. Mitchell in 1977 [1]. The modular, scalable display was initially designed with hundreds of MV50 LEDs and a newly available TTL (transistor transistor logic) memory addressing circuit from National Semiconductor[2]. The 1/4 inch thin flat panel prototype and the scientific paper were each displayed.[3] at the 29th Engineering Exposition in Anaheim May 1978, organized by the Science Service in Washington D.C. The LED TV display received awards and recognition from NASA[4], General Motors Corporation[5], and faculty from area Universities[6]. The event was open to the public including U.S. and foreign representatives. The monochromatic LED prototype remains operational. A LCD(liquid crystal display) matrix design was also cited in the LED paper as an alternative x-y scan technology and as a future alternate television display method. The concept or significance of replacing the 50 year+ high-voltage analog system (electron beam, and horizontal and vertical deflection systems)with a digital x-y scan system was very significant. Displacement of the magnetic scan systems eventialy may also have led to the displacement of deflection and convergence circuits. The revolutinary digital x-y scan system has helped the television to collaps into it's current thin form factor.
In 1978, Mitchell also submitted his paper to the Westinghouse Science Talent Search contest, where he received an Honerable Mention.
Contact information: Society for Science & the Public 1719 N Street N.W. , Washington, DC 20036, 202-785-2255.
Additionally, Mitchell presented his paper at the 90th Session of The Iowa Academy of Science April 21-22, 1978, at the University of Northern Iowa, Cedar Falls, Iowa
Note: This 1977 model was monochomatic by design. Efficient blue LEDs did not arrive for another decade. Large displays now use high-brightness diodes for a wide spectrum of colors. After more than 31 years since this prototype, in-home televisions makers have yet to implement a full true LED design.
See also
References
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This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (June 2009) |
- ^ Mitchell's modular LED x-y (horizontally and vertically scanned) system was cited in the 29th International Science and Engineering Exposition "book of abstracts", page 97, published by the "Science Service", Washington D.C. in May of 1978.
- ^ A technical reference detailing the LED display array, RF interface and scanning circuit was included as part of the 1978 29th ISEF exhibition in Anaheim Convention Center, Anaheim Ca. The original documents are kept with the prototype.
- ^ The prototype and scientific paper "Light Emitting Diode Television Screen" were part of exhibit #635. The original technical paper is kept with the original working prototype.
- ^ Honorable Mention - NASA, 29th ISEF "Announcement of Awards", page 4, Saturday May 13th 1978, published by the Science Service 1719 N Street Washington D.C. 20036.
- ^ 3rd Grand Award - GM, corporate sponsor of the 1978 Science Service event. 1978 29th Annual ISEF "Announcement of Awards", page 5, (note: Intel corporation is the current sponsor of this event).
- ^ Reference; the project witness log, a non-published signature list maintained with the original display materials. A second reference listing sponsors and judges: Science Service, 29th ISEF "Program of Events", pages 9, 10 and 11.
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