Frontlight

A frontlight is a means of illuminating a display device, usually a liquid crystal display (LCD), which would otherwise be viewed in ambient light. This improves its performance in poor lighting conditions.^[1]

An LCD presents an image by absorbing some light passing through it. When an electric field is applied across the crystal, it changes the passing light so it will not pass through a polarization filter. This allows LCDs to operate at low power, as no energy needs to be spent generating light. Many battery-operated electronic devices, including most calculators and other devices use unilluminated LCDs.

An unilluminated LCD must be lit from the front. To use ambient light, the liquid crystal itself is sandwiched between a polarization filter and a reflective surface. The mirror makes the display opaque so it cannot be illuminated from the back. Most often a light source is placed around the perimeter of the LCD.

The frontlight has found a place among devices using E Ink displays such as E-readers. In an effort to make these devices look like paper some trade offs are made, one of the drawbacks is that they don't produce light, so you can't read when in dark areas. And you can't put the light behind it and call it a Backlight because the display is opaque. The solution; the frontlight, also sometimes marketed as a "reading light" in order to appeal to the non-nerd as seen in the ReMarkable Paper Pro.^[2]

Frontlights are relatively uncommon overall. Electroluminescent lights present a reflective surface when turned off. This allows for a backlit display which can also be used with ambient light. Such backlights are popular in digital watches. The monochromatic light from an electroluminescent source does not work well with color displays, however. An incandescent frontlight was therefore a popular accessory for the Nintendo's Game Boy line up until the first model of the Game Boy Advance; the Game Boy Advance SP introduced a frontlight, which made external lights redundant.

Devices using a frontlight

• GP32 FLU (2002)
• Game Boy Advance SP^[a] (2003)
• Nintendo DS^[b]
• Kindle Paperwhite (2013)
• Amazon Kindle (Since 2019)

See also

• LCD
• Backlight

Notes

1. AGS-001 only; the later AGS-101 revision used a backlight
2. Original model only; a later revision used a backlight, which was retained by all DS models since