An electronic visual display is a display device that can display images, video, or text that is transmitted electronically. Electronic visual displays include television sets, computer monitors, and digital signage. They are ubiquitous in mobile computing applications like tablet computers, smartphones, and information appliances. Many electronic visual displays are informally referred to as screens.
Starting in the early 2000s, flat-panel displays began to dominate the industry, as cathode-ray tubes (CRT) were phased out, especially for computer applications. Starting in the mid 2010s, curved display panels began to be used in televisions, computer monitors, and smartphones.
There are various technologies used for electronic visual displays:
An overhead projector can be considered a type of electronic visual display.
Additionally, CRTs were widely used in the past and microLED displays are under development.
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).
| Electronic visual displays | ||
| Active displays | Passive displays | |
|---|---|---|
| present visual information by emitting light | present visual information by modulating light | |
| Principle | 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 |
| Principle | 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: |
| Principle | 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: |
| Principle | Photoluminescence | Electrowetting |
| Example | Plasma display panel (PDP) | Research & manufacturing: |
| Principle | Incandescence | Electromechanical modulation |
| Example | Numitron, a 7-segment numerical display tube | flap display flip-disk display digital micromirror device (DMD) Interferometric modulator display (IMOD) FTIR (unipixel) |
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 built 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 can be displayed (symbols, signs), simple numerals (7-segment layout) or arbitrary shapes can be formed (dot-matrix displays).
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] | |
| 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 | |
Each sub-pixel of a display device 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.
| 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 be 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)). | ||