CRT monitors Vs LCD monitors?
6 Feb 07
I prefer LCD to CRT, because according to me, LCD monitor better than CRT monitor. The advantages of LCD monitor are : 1. Its radiation to our eyes is lower than radiation of CRT monitor to our eyes. 2. Its resolution is better than CRT monitor. 3. etc. But the LCD monitor is more expensive than the CRT monitor.
6 Feb 07
I use lcd monitors now for the reasons that they look cool and are space savers even for their size. I have 3 24" lcd dell monitors working on 1 pc. They also don't consume as much power as a crt does and mine even has a built-in tv tuner and speakers with picture-in-picture. But in terms of performance of the same size the crt still wins. CRT's have a lower dot pitch and have a higher refresh rate. Those are 2 factors that tops my list. If only the CRT weren't that bulky.
6 Feb 07
A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is prized by engineers because it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices. Each pixel of an LCD consists of a layer of liquid crystal molecules aligned between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. With no liquid crystal between the polarizing filters, light passing through one filter would be blocked by the other. The surfaces of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using a cloth (the direction of the liquid crystal alignment is defined by the direction of rubbing). Before applying an electric field, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces. In a twisted nematic device (the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular, and so the molecules arrange themselves in a helical structure, or twist. Because the liquid crystal material is birefringent (i.e. light of different polarizations travels at different speeds through the material), light passing through one polarizing filter is rotated by the liquid crystal helix as it passes through the liquid crystal layer, allowing it to pass through the second polarized filter. Half of the light is absorbed by the first polarizing filter, but otherwise the entire assembly is transparent. When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field, distorting the helical structure (this is resisted by elastic forces since the molecules are constrained at the surfaces). This reduces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules are completely untwisted and the polarization of the incident light is not rotated at all as it passes through the liquid crystal layer. This light will then be polarized perpendicular to the second filter, and thus be completely blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts, correspondingly illuminating the pixel. With a twisted nematic liquid crystal device it is usual to operate the device between crossed polarizers, such that it appears bright with no applied voltage. With this setup, the dark voltage-on state is uniform. The device can be operated between parallel polarizers, in which case the bright and dark states are reversed (in this configuration, the dark state appears blotchy). Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided by applying either an alternating current, or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field). When a large number of pixels is required in a display, it is not feasible to drive each directly since then each pixel would require independent electrodes. Instead, the display is multiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together (typically in columns), and each group gets its own voltage source. On the other side, the electrodes are also grouped (typically in rows), with each group getting a voltage sink. The groups are designed so each pixel has a unique, unshared combination of source and sink. The electronics, or the software driving the electronics then turns on sinks in sequence, and drives sources for the pixels of each sink. Important factors to consider when evaluating an LCD monitor include * resolution: unlike CRT monitors, LCD monitors have a native-supported resolution for best display effect. * dot pitch: the granularity of LCD pixels. The smaller, the better. * viewable size: The length of diagonal of a LCD panel * response time (sync rate) * matrix type (passive or active) * viewing angle * color support: How many types of colors are supported. * brightness * contrast ratio * aspect ratio: 4 by 3, 16 by 9, 16 by 10, etc. * input ports (e.g. DVI, VGA, or even S-Video ). * 1904: Otto Lehmann publishes his work "Liquid Crystals" * 1911: Charles Mauguin describes the structure and properties of liquid crystals. * 1936: The Marconi Wireless Telegraph company patents the first practical application of the technology, "The Liquid Crystal Light Valve". * 1962: The first major English language publication on the subject "Molecular Structure and Properties of Liquid Crystals", by Dr. George W. Gray. Pioneering work on liquid crystals was undertaken in the late 1960s by the UK's Royal Radar Establishment at Malvern. The team at RRE supported ongoing work by George Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals (which had correct stability and temperature properties for application in LCDs). The first operational LCD was based on the Dynamic Scattering Mode (DSM) and was introduced in 1968 by a group at RCA in the USA headed by George Heilmeier. Heilmeier founded Optel, which introduced a number of LCDs based on this technology. In December 1970, the twisted nematic field effect in liquid crystals was filed for patent by Martin Schadt and Wolfgang Helfrich, then working for the Central Research Laboratories of Hoffmann-LaRoche in Switzerland (Swiss patent No. 532 261). Hoffmann-La Roche then licensed the invention to the Japanese electronics industry which soon produced the first digital quartz wrist watches with TN-LCDs and numerous other products. James Fergason at Kent State University filed an identical patent in the USA in February 1971. In 1971 the company of Fergason ILIXCO (now LXD Incorporated) produced the first LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due improvements of lower operating voltages and lower power consumption. In 1972, the first active-matrix liquid crystal display panel was produced in the United States by T. Peter Brody.As of 2007, the largest LCD panel in the world is a 108" panel developed by Sharp Corporation.