Illumination and direct view
The way in which high brightness LEDs are used can be divided into two broad categories, namely direct view applications and lighting (or illumination).
In lighting applications, the LED is used to illuminate a surface, a space or an object, rather than being viewed directly. Examples include flashlights, building façade lighting, backlighting of displays and keypads in mobile phones, and machine vision lighting.
In direct view applications, the LED light is used to convey information, for example in message signs and full-color video displays where LEDs form the pixels of the display panel. Signals are also direct view applications; examples include traffic signals, and brake lights and turn indicators on vehicles.
The largest use for high-brightness LEDs is in mobile appliances such as phone handsets and PDAs. LEDs are used as backlights for liquid-crystal display screens - single-color (blue or green) devices are used for monochrome displays while white LEDs are used to backlight full-color displays. Blue or white LEDs are also used to illuminate the keypads, while white LEDs are also being used for the flash function in phones with built-in digital cameras.
Another major application category is signs and displays, ranging from full-color video displays seen in sports stadiums and shopping malls to single-color message displays. This category is roughly equivalent in size to the vehicle market; LEDs are used to provide exterior signaling functions such as brake lights and turn indicators on many types of vehicle, and are also used in the interior of cars particularly to illuminate the instrument panels.
There are many examples of the use of LEDs in illumination applications - but as yet this segment accounts for only about 5% of the HB-LED market.
While LEDs are likely to continue to penetrate most if not all of their current markets, new application areas are set to emerge in the coming years. Two examples are the backlighting of large LCD panels, and automotive headlights. Whether or not LEDs will replace incumbent lighting sources in general illumination remains a subject for debate...