Backlighting Methods

The most common method for backlighting a display is the cold cathode fluorescent tube (CCFT) not unlike the fluorescent tubes used for office building lighting. They are narrow diameter tubes that are extraordinarily bright. These types of backlights are relatively easy to manufacture. They can be configured as an array directly behind the display or as (single, double, or L-shaped) edge lights.

In today’s mobile displays, white LEDs are being used more and more often as the cost of these devices continues to improve. They have the following advantages: Small form factor Can be continuously dimmed Reduced EMI Can be operated at extremely low temperatures Some customers also feel they are easier to use in a rugged application. While it is possible to make a CCFT more rugged, drop tests may be passed more easily with LEDs. CCFT backlights have difficulty operating at extremely low temperatures due to the increase in strike voltage to start the fluorescent tubes. Sharp has developed a self-heating backlight solution for the low temperature operation required for automotive displays.