Video walls and projectors are the large displays used at work. A video wall is one big picture made from many screens mounted edge to edge. A projector throws a picture onto a screen with light. They are used in metro and power-grid control rooms, broadcast studios, cinemas, lecture halls and hospitals.
A video wall is built from flat panels with very thin borders, so the joins between them are narrow. Some walls use LED tiles instead, which have no border at all. A wall controller, a computer behind the wall, takes in many video sources at once: camera feeds, maps and computer screens. It arranges them as windows anywhere on the wall. One camera feed can fill the whole wall, or thirty feeds can share it. Control-room walls must run day and night for years. So the panels are matched in colour and brightness, and the controller has a spare power supply.
Imagine the operations control centre of a metro line in Ahmedabad, the room from which staff watch and control every train. The wall in front of them is 4 panels high and 8 panels wide: 32 displays of 55 inches each, almost 10 metres across. The middle of the wall shows a live map of the line, with each train's position taken from the signalling system. The edges show feeds from station cameras, chosen through the video management system. When a passenger presses the emergency button in a train near one station, the operator drags that train's camera feed to the centre and enlarges it across four panels. The line map keeps running around it, so no other train drops out of sight.
Projectors now mostly use lasers as their light source, instead of lamps. A laser source lasts about 20,000 hours or more, while a lamp has to be replaced every few thousand hours. In cinemas, a projector receives each film from a digital cinema server and must meet strict standards for brightness and colour. In meeting rooms and lecture halls, the projector is one part of the room's AV system.
Some professionals look at a screen to check a picture, not just to see it. In a broadcast control room, engineers watch each channel on reference monitors, whose colours are exact, before and while it goes on air. This is part of broadcast monitoring. In a hospital, a radiologist, a doctor who reads X-rays and other scans, reads them on a medical display. Its greys are calibrated to a medical standard, so that a faint shadow on a chest X-ray is not lost. The scans come from the hospital's PACS, the system that stores and displays medical images.
The makers of these displays write much of their control and calibration software in India, including in Delhi and Pune.