Liquid-crystal display
Illumination

Since LCDs produce no light of their own, they require external light to produce a visible image. In a transmissive type of LCD, the light source is provided at the back of the glass stack and is called a backlight. Active-matrix LCDs are almost always backlit. Passive LCDs may be backlit but many are reflective as they use a use a reflective surface or film at the back of the glass stack to utilize ambient light. Transflective LCDs combine the features of a backlit transmissive display and a reflective display.

The common implementations of LCD backlight technology are:

Today, most LCD screens are being designed with an LED backlight instead of the traditional CCFL backlight, while that backlight is dynamically controlled with the video information (dynamic backlight control). The combination with the dynamic backlight control, invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan, simultaneously increases the dynamic range of the display system (also marketed as HDR, high dynamic range television or FLAD, full-area local area dimming).

The LCD backlight systems are made highly efficient by applying optical films such as prismatic structure (prism sheet) to gain the light into the desired viewer directions and reflective polarizing films that recycle the polarized light that was formerly absorbed by the first polarizer of the LCD (invented by Philips researchers Adrianus de Vaan and Paulus Schaareman), generally achieved using so called DBEF films manufactured and supplied by 3M. Improved versions of the prism sheet have a wavy rather than a prismatic structure, and introduce waves laterally into the structure of the sheet while also varying the height of the waves, directing even more light towards the screen and reducing aliasing or moiré between the structure of the prism sheet and the subpixels of the LCD. A wavy structure is easier to mass-produce than a prismatic one using conventional diamond machine tools, which are used to make the rollers used to imprint the wavy structure into plastic sheets, thus producing prism sheets. A diffuser sheet is placed on both sides of the prism sheet to distribute the light of the backlight uniformly, while a mirror is placed behind the light guide plate to direct all light forwards. The prism sheet with its diffuser sheets are placed on top of the light guide plate. The DBEF polarizers consist of a large stack of uniaxial oriented birefringent films that reflect the former absorbed polarization mode of the light. Such reflective polarizers using uniaxial oriented polymerized liquid crystals (birefringent polymers or birefringent glue) are invented in 1989 by Philips researchers Dirk Broer, Adrianus de Vaan and Joerg Brambring. The combination of such reflective polarizers, and LED dynamic backlight control make today's LCD televisions far more efficient than the CRT-based sets, leading to a worldwide energy saving of 600 TWh (2017), equal to 10% of the electricity consumption of all households worldwide or equal to 2 times the energy production of all solar cells in the world.
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