An electronic visual display is display technology which incorporates flat panel displays, performs as a video display, output device for presentation of images transmitted electronically, for visual reception, without producing a permanent record.
Common applications for electronic visual displays used to be television sets or computer monitors, but these days electronic visual displays tend to be ubiquitous as interface for large amounts of visual information in mobile computing applications like portable information communication technology devices. They can also be found in digital signage.
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Electronic visual displays present visual information according to the electrical input signal (analog or digital) either by emitting light (then they are called active displays) or, alternatively, by modulating available light during the process of reflection or transmission (light modulators are called passive displays).
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| Electronic visual displays | ||
| Active displays | Passive displays | |
|---|---|---|
| present visual information by emitting light | present visual information by modulating light | |
| Effect | Liquid crystal display (LCD) + backlight (this combination is considered an active display) |
LCD |
| Example | LCD TV screen, LCD computer monitor | LCD watch (reflective) see LCD classification |
| Effect | Cathodoluminescence | Electrophoresis also see Electronic paper |
| Example | Cathode ray tube (CRT) Field emission display (FED) Vacuum fluorescent display (VFD) Surface-conduction electron-emitter display (SED) |
Research & manufacturing: E Ink electronic paper displays SiPix Microcup Electronic Paper |
| Effect | Electroluminescence | Electrochromism |
| Example | (thin or thick film) electro-luminescence (EL) (inorganic or organic) light emitting diode (LED, OLED) gas discharge display (Nixie tube) |
Research & manufacturing: ntera NanoChromics Technology |
| Effect | Photoluminescence | Electrowetting |
| Example | Plasma display panel (PDP) | Research & manufacturing: Liquavista |
| Effect | Incandescence |
Electromechanical modulation |
| Example | Numitron, a 7-segment numerical display tube Numitron website | flap display flip-disk display digital micromirror device (DMD) Interferometric modulator display (IMOD) FTIR (unipixel) telescopic pixel display |
Electronic visual displays can be observed directly (direct view display) or the displayed information can be projected to a screen (transmissive or reflective screen). This usually happens with smaller displays at a certain magnification.
| Display modes of observation | |
|---|---|
| Direct view display | Projection display |
| transmissive mode of operation | front-projection (with reflective screen) e.g. video projector |
| reflective mode of operation | rear-projection (with transmissive screen) e.g. rear projection television screen |
| transflective mode of operation (e.g. transflective LCD) |
retinal projection (with or without combiner) e.g. head mounted display |
A different kind of projection display is the class of "laser projection displays" where the image is build up sequentially either via line by line scanning or by writing one complete column at a time. For that purpose one beam is formed from three lasers operating at the primary colors and this beam is scanned electro-mechanically (galvanometer scanner, micro-mirror array)) or electro-acousto-optically.
Depending on the shape and on the arrangement of the picture elements of a display either fixed information ca be displayed (symbols, signs), simple numerals (7-segment layout) or arbitrary shapes can be formed (dot-matrix displays).
| Layout of picture elements | |
|---|---|
| Segmented displays characters, numbers and symbols of fixed shape (may be multiplex addressed) The following layouts are well known: Seven-segment display Fourteen-segment display Sixteen-segment display |
Dot-matrix displays sub-pixels are arranged in a regular 2-dimensional array (multiplex addressing required); arbitrary shapes can be formed and displayed |
Colors can be generated by selective emission, by selective absorption, transmission or by selective reflection.
| Color emission and control | |
|---|---|
| additive mixing primary colors add up to produce white light |
subtractive mixing filters, dyes, pigments (e.g.printing) subtract (absorb) parts of white light |
| temporal mixing (additive) e.g. rotating primary color filter wheel in projectors |
spatial mixing (additive) closely spaced sub-pixels |
| spatio temporal color mixing combined spatial and temporal mixing[1] |
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| arrangement of sub-pixels for additive color mixing see sub-pixel arrangements 1 see sub-pixel arrangements 2 see sub-pixel arrangements 3 |
subtractive color mixing does not require special sub-pixel arrangements all components (e.g. filters) have to be in the same path of light. |
| Examples: stripe delta-nabla PenTile arrangement, e.g. RGB+White |
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Each sub-pixel of a display devices must be selected (addressed) in order to be energized in a controlled way.
| Addressing modes (selection of picture elements) | |
|---|---|
| direct addressing each individual picture element has electrical connections to the driving electronics. |
multiplexed addressing several picture elements have common electrical connections to the driving electronics, e. g.. row and column electrodes when the picture elements are arranged in a two dimensional matrix. |
| active matrix addressing active electronic elements added in order to improve selection of picture elements.
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passive matrix addressing the nonlinearity of the display effect (e.g. LCD, LED)is used to realize the addressing of individual pixels in multiplex addressing. In this mode only a quite limited number of lines can be addressed. In the case of (STN-)LCDs this maximum is at ~240, but at the expense of a considerable reduction of contrast. |
| The matrix of active electronic elements can used in transmissive mode of operation (high transmittance required) or a non-transparent active matrix can be used for reflective LCDs (e.g. liquid crystal on silicon (LCOS)).| | |
| Driving modes (activation of picture elements) | |
|---|---|
| voltage driving activation of pixels by voltage (e.g. LCD field effects). If the current is low enough this mode may be the basis for displays with very low power requirements (e.g. μW for LCDs without backlight). |
current driving activation of pixels by electrical current (e.g. LED). |