It is not uncommon to drive through the major cities in the
world and come upon one or more full color display screens.
Invariably these brilliant screens, showing moving or still
pictures with vivid colors, are made up of red, blue and green
light emitting diodes (LED's). Much rapid growth has been
made in the installations of full color video LED's display
screens since their early appearance in 1995. The worldwide
market for these displays in 1999 is estimated to be US$
297 million, with growth of 128% over previous year in
North America and Europe [1]. The quick acceptance of
LED technology over current display technologies such as
incandescent lamp and ¯at display tube can be attributed to
the availability of ultra-bright green and blue LED's based
on indium gallium nitride technology to complement previously
available ultra-bright red color LED's. The strengths
of LED technology are high visibility, sunlight viewable,
long operation life, high reliability and resistance to the
environments, lower power consumption, lower weight and
thin pro®le, full range of power, wide range of color
spectrum, ¯exibility in design.
By 1999, LED technology was ®rmly established with its
proven low cost of ownership as there was no major competing
technology for the outdoor full color display market.
It is a different story for the indoor full color video display
market. See Fig. 1 for an example of an indoor LED display
screen.
In the indoor display market, there are a number of
competing technologies, which provide similar or acceptable
performance, and cost is often the deciding factor. The
indoor environment requires the LED screen to have higher
resolution (more LED's per unit area) and wider viewing
angle because of shorter viewing distance; lower screen
brightness but higher color uniformity; reduced protection
against the elements and less supporting structure. The
requirements and their impact on cost are summarized in
Table 1.