Cathode ray tube

The cathode ray tube or CRT, invented by Karl Ferdinand Braun, is the display device used in most computer displays, video monitors, televisions and oscilloscopes. The CRT developed from Philo Farnsworth's work was used in all television sets until the late 20th century and the advent of plasma screens, LCDs, DLP, OLED displays, and other technologies.

Health danger

Some believe the electromagnetic fields emitted by CRT monitors constitute a health danger to the functioning of living cells. Exposure to these fields is far lower at distances of 85 cm or farther. It is also less intensive for the display's user than for a person located behind it.

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CRTs also emit very small amounts of X-rays as a result of the electron beam's bombardment of the shadow mask/aperture grille and phosphors. Almost all of this radiation is blocked by the thick leaded glass in the screen so the amount of radiation escaping the front of the monitor is mostly harmless. The Food and Drug Administration regulations in 21 CFR 1020 are used to strictly limit, for instance, television receivers to 0.5 milliroentgens per hour (mR/h) (0.13 µC/(kg·h) (at a distance of 5 cm from any external surface and as mentioned above, most CRT emissions fall well below this limit.http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=1020.10

Related Topics:
X-rays - Food and Drug Administration

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Old CRTs may also have used toxic phosphors, although that is much less common today. An implosion or other breaking of the glass envelope could release these toxic phosphors. And because of the X-ray hazard, the glass envelopes of most modern CRTs are made from heavily leaded glass. The lead in this glass may represent an environmental hazard, especially in the presence of acid rain leaching through landfills.

Related Topics:
Leaded glass - Lead - Acid rain - Landfill

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The constant refreshing of a CRT can cause seizures in epileptics, if they are photosensitive. Filters are available to reduce these effects.

Related Topics:
Seizures - Epileptics - Photosensitive

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A high refresh rate (above 75 Hz) also helps to negate these effects.

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CRTs operate at very high voltages. These voltages can persist long (several days) after the device containing the CRT has been switched off and unplugged. Do not tamper with devices containing CRT tubes unless you have proper engineering training and have taken appropriate precautions. Since the CRT contains a vacuum, care should be taken to prevent implosion.

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