Backlight
[1] Typical sources of light for backlights include light-emitting diodes (LEDs) and cold cathode fluorescent lamps (CCFLs).
A review of some early backlighting schemes for LCDs is given in a report Engineering and Technology History by Peter J.
CCFL backlights are used on larger displays such as computer monitors, and are typically white in color; these also require the use of an inverter and diffuser.
The actual red, green, and blue points can be moved farther out so that the display is capable of reproducing more vivid colors.
The manufacturer, Nanosys, claims that the color output of the dots can be tuned precisely by controlling the size of the nanocrystals.
Other companies pursuing this method are Nanoco Group PLC (UK), QD Vision, 3M a licensee of Nanosys and Avantama of Switzerland.
[14][15] Sony has adapted quantum dot technology from the US company QD Vision[16] to introduce LCD TVs with an improved edge-lit LED backlight marketed under the term Triluminos in 2013.
The use of three separate light sources for red, green, and blue means that the white point of the display can move as the LEDs age at different rates; white LEDs are affected by this phenomenon, with changes of several hundred kelvins of color temperature being recorded.
[citation needed] In 2010, current generation LED displays can have significant power consumption advantages.
This technology uses blue pump LEDs in combination with a sheet on which phosphorous luminescent materials are printed for colour conversion.
This arrangement allows for local dimming to obtain darker black pixels depending on the image displayed.
Using PWM (pulse-width modulation, a technology where the intensity of the LEDs are kept constant, but the brightness adjustment is achieved by varying a time interval of flashing these constant light intensity light sources[26]), the backlight is dimmed to the brightest color that appears on the screen while simultaneously boosting the LCD contrast to the maximum achievable levels If the frequency of the pulse-width modulation is too low or the user is very sensitive to flicker, this may cause discomfort and eye-strain, similar to the flicker of CRT displays.
If the object appears to have sharply defined edges as it moves, the backlight is strobing on and off at a fairly low frequency.
The flicker can be reduced or eliminated by setting the display to full brightness, though this may have a negative impact on image quality and battery life due to increased power consumption.
The LCD backlight systems are made highly efficient by applying optical films such as prismatic structure 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),[29] generally achieved using so called DBEF films manufactured and supplied by 3M.
[32] The combination of such reflective polarizers, and LED dynamic backlight control[23] 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.
As for other consumer electronics products (e.g., fridges or light bulbs), energy consumption categories are enforced for television sets.
[35] Standards for power ratings for TV sets have been introduced, e.g., in the USA, EU, and Australia[36] as well as in China.
