CRT screens have much deeper cabinets compared to LCD screens for a given screen size. LCDs have generally inferior color rendition due to the fluorescent lights that can be used as backlights, even though they can be brighter overall. CRTs can be useful for displaying photos with a high pixel per unit area and correct color balance. The end of most high-end CRT production in the mid 2000s (including high-end Sony, and Mitsubishi product lines) means an erosion of the CRT's capability. Samsung did not introduce any CRT models for the 2008 model year at the 2008 Consumer Electronics Show and on February 4, 2008 Samsung removed their 30" wide screen CRTs from their North American website and has not replaced them with new models.
General, rear-projection displays and LCDs require less power per display area, but plasma displays consume as much as or more than CRTs. However, CRTs still find adherents in computer gaming because of higher resolution per initial cost and fast response time. CRTs are often used in psychological research that requires precise recording of reaction times. CRTs are also still popular in the printing and broadcasting industries as well as in the professional video, photography, and graphics fields due to their greater color fidelity and contrast, better resolution when displaying moving images, and better view from angles, although improvements in LCD technology increasingly alleviate these concerns. The demand for CRT screens is falling rapidly, and producers are responding to this trend. For example, in 2005 Sony announced that they would stop the production of CRT computer displays.
Similarly, German manufacturer Loewe ceased production of CRT TVs in December 2005. It has been common to replace CRT-based televisions and monitors in as little as 5–6 years, although they generally are capable of satisfactory performance for a much longer time.
TOXICITY
CRTs may contain toxic phosphors within the glass envelope. The glass envelopes of modern CRTs may be made from heavily leaded glass, which represent an environmental hazard. Indirectly heated vacuum tubes (including CRTs) use barium compounds and other reactive materials in the construction of the cathode and getter assemblies; normally this material will be converted into oxides upon exposure to the air, but care should be taken to avoid contact with the inside of all broken tubes.
In some jurisdictions, discarded CRTs are regarded as toxic waste. In October 2001, the United States Environmental Protection Agency created rules stating that CRTs must be brought to special recycling places. In November 2002, the EPA began fining companies that disposed of CRTs through landfills or incineration. Regulatory agencies, local and statewide, monitor the disposal of CRTs and other computer equipment.
The constant refreshing of a CRT can cause headaches and seizures in epileptics. Screen filters are available to reduce these effects. A high refresh rate (above 72 Hz) also helps to negate these effects.
Under some circumstances the signal radiated from the electron guns and associated wiring can be reconstructed to remotely display what is shown on the CRT.
HIGH VOLTAGE
CRTs operate at very high voltages, which can persist long after the device containing the CRT has been switched off and/or unplugged. Residual charges of hundreds of volts can also remain in large capacitors in the power supply circuits of the device containing the CRT; these charges may persist.
Modern circuits contain bleeder resistors, to ensure that the high-voltage supply is discharged to safe levels within a couple of minutes at most. These discharge devices can fail even on a modern unit and leave these high voltage charges present. The final anode connector on the bulb of the tube carries this high voltage.
A high vacuum exists within all CRT monitors. If the outer glass envelope is damaged, a dangerous implosion may occur. Due to the power of the implosion, glass may explode outwards. This shrapnel can travel at dangerous and potentially fatal velocities. While modern CRT used in televisions and computer displays have epoxy-bonded face-plates or other measures to prevent shattering of the envelope, CRTs removed from equipment must be handled carefully to avoid personal injury.
Early TV receivers had safety glass in front of their CRTs for protection. Modern CRTs have exposed faceplates; they have tension bands around the widest part of the glass envelope, at the edge of the faceplate, to keep the faceplate's glass under considerable compression, greatly enhancing resistance to impact. The tension in the band is on the order of a ton or more.
The CRT or cathode ray tube, is the picture tube of a monitor. The back of the tube has a negatively charged cathode. The electron gun shoots electrons down the tube and onto a charged screen. The screen is coated with a pattern of phosphor dots that glow when struck by the electron stream. Each cluster of three dots, one of each color, is one pixel.
The image on the monitor's screen is usually made up from at least tens of thousands of such tiny dots glowing on command from the computer. The closer together the pixels are, the sharper the image on screen can be. The distance between pixels on a computer monitor screen is called its dot pitch and is measured in millimeters. Most monitors have a dot pitch of 0.28 mm or less.
There are two electromagnets around the collar of the tube which deflect the electron beam. The beam scans across the top of the monitor from left to right, is then blanked and moved back to the left-hand side slightly below the previous trace (on the next scan line), scans across the second line and so on until the bottom right of the screen is reached. The beam is again blanked, and moved back to the top left to start again. This process draws a complete picture, typically 50 to 100 times a second. The number of times in one second that the electron gun redraws the entire image is called the refresh rate and is measured in hertz (cycles per second). It is common in television or very early computer equipment, to use a technique called interlacing, in which all the odd-numbered lines of an image are traced, and then all the even-numbered lines; the circuitry of such an interlaced display need be capable of only half the speed of a non-interlaced display. An interlaced display, particularly at a relatively low refresh rate, can appear to some observers to flicker, and may cause eyestrain.
Health concerns
It has been claimed that the electromagnetic fields emitted by CRT monitors constitute a health hazard, and can affect the functioning of living cells. However, studies that examined this possibility showed no signs that CRT radiation had any effect on health.
Exposure to these fields diminishes considerably at distances of 85 cm or farther according to the inverse square law, which describes the propagation of all magnetic radiation.
As the coils in a CRT monitor are extremely inefficient antennas, there is little electromagnetic field radiated.
CRTs can emit a small amount of X-ray radiation as a result of the electron beam's bombardment of the shadow mask/aperture grille and phosphors. The amount of radiation escaping the front of the monitor is widely considered unharmful.
The Food and Drug Administration regulations in 21 C.F.R. 1020.10 are used to strictly limit, for instance, television receivers to 0.5 mill roentgens per hour (mR/h) (0.13 µC/(kg·h) or 36 pA/kg) at a distance of 5 cm from any external surface; since 2007, most CRTs have emissions that fall well below this limit. This is one of the reasons CRT equipment sold in the
Early color television receivers (many of which are now highly collectible, see CT-100) were especially vulnerable due to primitive high-voltage regulation systems. X-ray production is generally negligible in black-and-white sets (due to low acceleration voltage and beam current), and in virtually every color display since the late 1960s, when systems were added to shut down the horizontal deflection system (and therefore high voltage supply) should regulation of the acceleration voltage fail.
All television receivers and CRT displays equipped with a vacuum tube based high-voltage rectifier or high-voltage regulator tube also generate X-rays in these stages. These stages are universally housed in a metal enclosure called the "high-voltage cage" made from sheet metal to substantially reduce (and effectively eliminate) exposure. For both X-ray and electrical safety reasons, the set should never be operated with the cover of the high voltage cage opened. Many sets incorporated some type of interlock system to prevent operation with the high voltage cage open.
CRTs may emit low levels of beta radiation which can be detectable by sensitive Geiger counter. It does not come from accelerated electrons in the tube but from radioactive isotopes. Source of this type of radioactivity is mainly Zirconium or other isotopes sometimes used in glass or mask production.
