Backlights are used in a wide range of applications in which illumination is needed. This typically includes televisions, computer monitors, keypads, keyboards and similar applications. Up until 2010, however, cold cathode fluorescent lamp (CCFL) has been the preferred backlighting technology for liquid-crystal displays (LCDs). Today, light-emitting diode (LED) is the industry’s leading backlighting technology.
There are two different types of LED backlights: white and RGB. White LED backlights are generally used to illuminate electronic displays for laptop screens and computer monitors. They are so common, in fact, that white LEDs account for nearly all mobile LCD displays. The name “white LED” is somewhat of a misnomer, however. Although its name would suggest otherwise, white LED backlights actually have a blue LED with a broad spectrum yellow. This combination creates the appearance of white light.
On the other hand, RGB LEDs feature a combination of red, blue and green colors (hence the name). They are easily configured to produce different color temperatures of white. While white LEDs are typically used in laptop screens and computer monitors, RGBs are used in high-end displays. Because they have three separate LEDs, RGB LEDs produce color spectrum that closely matches the filter in the pixel. As a result, it improves the quality of the display by blocking less light when white is being illuminated.
Normally, most LED backlights use either white or RGB illumination. However, there’s a third method that’s recently gaining momentum. It involves illumination a layer of micro-sized phosphor crystals to convert blue wavelengths into longer wavelengths as green and red colors. Pioneered by Nanosys, this backlighting technology is still new and not widely adopted. Nonetheless, research shows that color output of the dots can be controlled by changing the size of the phosphor crystals.
Regardless of the type, LED backlights are typically edge lit, meaning the LEDs are arranged on the edges of the display. This allows for a thinner construction while also cutting down on production costs. In comparison, full-array or direct backlights are more resource-intensive.
It’s important to note that LED backlights are typically dimmed with pulse-width modulation to the current. This switches the backlight off and on, similar to the behavior of a strobe light. If the pulse-width modulation is too low, however, this may cause eye strain. Therefore, companies must design their LED backlights with the appropriate pulse-width modulation to prevent this phenomenon from happening.