A liquid crystal display (LCD) device is well known. Since the LCD device is a light reception type device having no ability to emit light by itself, a separate light source unit is needed. Such a lighting apparatus used for the LCD device is called a “backlight unit”.
Generally, backlight units are classified into an edge lighting type and a direct lighting type in accordance with the arrangement of light sources (for example, light emitting diodes (LEDs)).
In the edge lighting type, light sources (for example, LEDs) are arranged at a side surface of a light guide plate to guide light. This edge lighting type backlight unit is applied to relatively-small LCD devices such as monitors for desktop computers and notebooks. The edge lighting type exhibits excellent light uniformity and superior durability.
On the other hand, the direct lighting type is applied to middle/large display devices of 20 inches or more. In the direct lighting type backlight unit, light sources are arranged beneath a liquid crystal panel to directly illuminate the entire surface of the liquid crystal panel.
Generally, backlight units have a configuration including LEDs mounted on a bar-shaped circuit board, a light guide plate (LGP), a reflective sheet, and an optical sheet.