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In
home cinema Home cinema, also called home theaters or theater rooms, are home entertainment audio-visual systems that seek to reproduce a movie theater experience and mood using consumer electronics-grade video and audio equipment that is set up in a roo ...
and
video editing Video editing is the manipulation and arrangement of video shots. Video editing is used to structure and present all video information, including films and television shows, video advertisements and video essays. Video editing has been dramaticall ...
technology, bias lighting is a weak
light source Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahe ...
on the backside of a screen or monitor that illuminates the wall or surface behind and just around the display.


Motivation

The purpose of bias lighting is to reduce the perceived brightness of the display as a result of the contrast with the slightly illuminated area around it. This reduces the eye strain and fatigue that occurs when viewing a bright display against a very dark background for an extended time, and increases the perceived blackness, perceived highlights and overall contrast of the display.


History

Bias lighting has been used since the early days of television in the form of "TV lamps", often taking the shape of an animal, that were set atop television sets and projected light onto the wall behind the set. As of the 2000s, bias lights often use
LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s, attach to the backside of
flat-panel displays A flat-panel display (FPD) is an electronic display used to display visual content such as text or images. It is present in consumer, medical, transportation, and industrial equipment. Flat-panel displays are thin, lightweight, provide better l ...
, and draw power from a
USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad v ...
port. Some bias lighting kits even use a webcam pointed at a TV or monitor screen to read colors and change television backlights accordingly. They may also be integrated into the display. Some
Philips Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters i ...
televisions since 2002, for example, feature integrated bias lights with the brand name "Ambilight". Color-changing lights like this should not be used in professional editing environments or where image fidelity is important.


Color temperature

Bias lights with a
color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
of 6,500 K match the temperature of most monitors' white color, which is derived from the
CIE standard illuminant D65 CIE standard illuminant D65 (sometimes written D65) is a commonly used standard illuminant defined by the International Commission on Illumination (CIE). It is part of the D series of illuminants that try to portray standard illumination conditio ...
. They are used in professional editing environments and are recommended to maximize the fidelity of the perceived image. In home cinema, bias lighting that is no brighter than 10% of the display's brightest spot and with a
color rendering index A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with a natural or standard light source. Light sources with a high CRI are desirable in ...
of at least 90 is recommended. There is some debate about the proper brightness levels of bias lighting for HDR content, with SMPTE recommending 4.5 nits and the Imaging Science Foundation recommending 10%, but sometimes as high as 15%.


See also

*
Background light A background light is used to illuminate the background area of a set. The background light will also provide separation between the subject and the background. Many lighting setups follow a three-point lighting or four-point lighting setup. Fo ...
, lighting used to illuminate the background area of a set in theatre and film


References

{{reflist Film and video technology Lighting