The present invention relates to billboards or other large displays. Billboards are a type of outdoor advertising found, for example, along major highways. The name refers to large, outdoor steel-framed signs, which in some installations are mounted on poles or on a base to be elevated above the ground. Most often, the artwork (which in the present application includes broadly advertising materials or other content to be displayed) forming the sign is printed on large poster sheets, which are affixed to the face of the billboard. There are hundreds of thousands of billboards in the United States, generating billions of U.S. dollars in revenues.
A billboard frame is typically constructed from steel beams and supports the artwork. If the billboard is to be illuminated at night, typically lighting equipment is mounted in front of the billboard on poles to shine light back towards the billboard. Standard sizes for a large steel frame assembly include 20 feet high×60 feet wide (6.1×18.3 m), 20 feet high×48 feet wide (6.1×14.6 m), 14 feet high×48 feed wide (4.2×14.6 m), and 10 feet high×36 feet wide (3×11 m). The front of the steel frame is covered with a backing material, known as a facing. The artwork is affixed to the facing. The artwork is either preprinted on paper or vinyl sheets that are pasted onto the facing, or in some cases, the art is painted directly onto a plywood or canvas facing.
Billboards designed to display advertising at night have traditionally been illuminated from the front by lamps mounted in front of, and below, the billboard, which shine light back towards the billboard face. Due to the limitation of lamps, the quality of nighttime illumination has been relatively poor. Particularly because billboards are used mostly for advertising purposes, it would be desirable to provide a billboard which can be used at night but with a lighting arrangement better than the current designs.
There are increasing needs for large area displays as digital display technology and billboard print technology improves, which place increase requirements on backlight systems that are low cost and convenient to set up.