In home cinema and video editing technology, bias lighting is a weak light source on the backside of a screen or monitor that illuminates the wall or surface behind and just around the display. [1] [2]
In home cinema and video editing technology, bias lighting is a weak light source on the backside of a screen or monitor that illuminates the wall or surface behind and just around the display. [1] [2]
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. [1] This reduces the eye strain and fatigue that occurs when viewing a bright display against a very dark background for an extended time, [1] and increases the perceived blackness, perceived highlights and overall contrast of the display. [1] [2]
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. [2] In 2002, Philips Consumer Electronics developed and patented [3] a lighting system that allowed the background illumination to follow the brightness and color of the TV image. In addition to reducing the brightness-contrast of the image with the background, this also extended the image across the wall, making it appear larger. This system was integrated into a flat TV and introduced to the market in 2004 under the name “Ambilight”. As of the 2000s, bias lights often use LEDs, attach to the backside of flat-panel displays, and draw power from a USB port. [2] Some bias lighting kits even use a webcam pointed at a TV or monitor screen to read colors and change television backlights accordingly. [4]
Bias lights with a color temperature of 6,500 K match the temperature of most monitors' white color, which is derived from the CIE standard illuminant D65. [1] They are used in professional editing environments and are recommended to maximize the fidelity of the perceived image. [1] [2] In home cinema, bias lighting that is no brighter than 10% of the display's brightest spot [2] and with a color rendering index of at least 90 is recommended. [1] [2] 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%.
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms on an oscilloscope, a frame of video on an analog television set (TV), digital raster graphics on a computer monitor, or other phenomena like radar targets. A CRT in a TV is commonly called a picture tube. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons.
Color temperature is a parameter describing the color of a visible light source by comparing it to the color of light emitted by an idealized opaque, non-reflective body. The temperature of the ideal emitter that matches the color most closely is defined as the color temperature of the original visible light source. The color temperature scale describes only the color of light emitted by a light source, which may actually be at a different temperature.
A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a visual display, support electronics, power supply, housing, electrical connectors, and external user controls.
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liquid crystals do not emit light directly but instead use a backlight or reflector to produce images in color or monochrome.
Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the characteristics of the human visual system.
Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. Gamma correction is, in the simplest cases, defined by the following power-law expression:
A plasma display panel is a type of flat-panel display that uses small cells containing plasma: ionized gas that responds to electric fields. Plasma televisions were the first large flat-panel displays to be released to the public.
Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants.
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.
An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector. To display images, LCD projectors typically send light from a metal-halide lamp through a prism or series of dichroic filters that separates light to three polysilicon panels – one each for the red, green and blue components of the video signal. As polarized light passes through the panels, individual pixels can be opened to allow light to pass or closed to block the light. The combination of open and closed pixels can produce a wide range of colors and shades in the projected image.
Digital light processing (DLP) is a set of chipsets based on optical micro-electro-mechanical technology that uses a digital micromirror device. It was originally developed in 1987 by Larry Hornbeck of Texas Instruments. While the DLP imaging device was invented by Texas Instruments, the first DLP-based projector was introduced by Digital Projection Ltd in 1997. Digital Projection and Texas Instruments were both awarded Emmy Awards in 1998 for the DLP projector technology. DLP is used in a variety of display applications from traditional static displays to interactive displays and also non-traditional embedded applications including medical, security, and industrial uses.
A backlight is a form of illumination used in liquid-crystal displays (LCDs) that provides illumination from the back or side of a display panel. LCDs do not produce light by themselves, so they need illumination to produce a visible image. Backlights are often used in smartphones, computer monitors, and LCD televisions. They are used in small displays to increase readability in low light conditions such as in wristwatches. Typical sources of light for backlights include light-emitting diodes (LEDs) and cold cathode fluorescent lamps (CCFLs).
Architectural lighting design is a field of work or study that is concerned with the design of lighting systems within the built environment, both interior and exterior. It can include manipulation and design of both daylight and electric light or both, to serve human needs.
Screen burn-in, image burn-in, ghost image, or shadow image, is a permanent discoloration of areas on an electronic visual display such as a cathode-ray tube (CRT) in an older computer monitor or television set. It is caused by cumulative non-uniform use of the screen.
A CRT projector is a video projector that uses a small, high-brightness cathode ray tube (CRT) as the image generating element. The image is then focused and enlarged onto a screen using a lens kept in front of the CRT face. The first color CRT projectors came out in the early 1950s. Most modern CRT projectors are color and have three separate CRTs, and their own lenses to achieve color images. The red, green and blue portions of the incoming video signal are processed and sent to the respective CRTs whose images are focused by their lenses to achieve the overall picture on the screen. Various designs have made it to production, including the "direct" CRT-lens design, and the Schmidt CRT, which employed a phosphor screen that illuminates a perforated spherical mirror, all within an evacuated cathode ray tube.
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. Four-point lighting is the same as three-point lighting with the addition of a background light. In a four-point lighting, the background light is placed last and is usually placed directly behind the subject and pointed at the background. By adding a background light to a set, filmmakers can add a sense of depth to shots.
Large-screen television technology developed rapidly in the late 1990s and 2000s. Prior to the development of thin-screen technologies, rear-projection television was standard for larger displays, and jumbotron, a non-projection video display technology, was used at stadiums and concerts. Various thin-screen technologies are being developed, but only liquid crystal display (LCD), plasma display (PDP) and Digital Light Processing (DLP) have been publicly released. Recent technologies like organic light-emitting diode (OLED) as well as not-yet-released technologies like surface-conduction electron-emitter display (SED) or field-emission display (FED) are in development to supersede earlier flat-screen technologies in picture quality.
Photographic lighting refers to how a light source, artificial or natural, illuminates the scene or subject that is photographed; put simply, it is lighting in regards to photography. Photographers can manipulate the positioning and the quality of a light source to create visual effects, potentially changing aspects of the photograph such as clarity, tone and saturation to create an accurate rendition of the scene.
An LED-backlit LCD is a liquid-crystal display that uses LEDs for backlighting instead of traditional cold cathode fluorescent (CCFL) backlighting. LED-backlit displays use the same TFT LCD technologies as CCFL-backlit LCDs, but offer a variety of advantages over them.
The Helmholtz–Kohlrausch effect is a perceptual phenomenon wherein the intense saturation of spectral hue is perceived as part of the color's luminance. This brightness increase by saturation, which grows stronger as saturation increases, might better be called chromatic luminance, since "white" or achromatic luminance is the standard of comparison. It appears in both self-luminous and surface colors, although it is most pronounced in spectral lights.
