Cathode ray tubes (CRT), once the only option for computer monitors, have been largely replaced by liquid crystal display screens (LCDs). Though CRTs still have an edge in speed and color fidelity, LCDs are slimmer, lighter and more energy-efficient. LCDs also have advantages when it comes to radiation, though there are many kinds of radiation. Monitors emit light and they radiate sound energy. They also emit other kinds of radiation and interference. Neither one is completely free of this, but LCDs come out ahead.
The CRT makes visible light when electrons inside the tube hit the phosphor coating just behind the screen. The LCD is a light filter, giving color to white light that passes through it. It needs a separate light source to work. Two types are currently used: fluorescent lighting and light-emitting diodes (LEDs). Fluorescent lamps are inexpensive, bright and compact. LEDs are more durable, but in 2009, the brightest ones are still more expensive.
CRTs can generate X-rays. While these X-rays are "soft," or low-energy, the CRTs are made with leaded glass as shielding so no harmful radiation reaches the user. The X-rays come from high voltages used to run the CRT. LCD screens run on much lower voltages, so they don't create X-rays.
CRTs are notorious for making a soft, high-pitched whine. The horizontal scan rate, the frequency at which the electron gun "paints" across the screen, is at the upper range of human hearing. It can be a bother for some people. Though LCD monitors work on a totally different principle, they, too, can whine.
CRTs can emit a small amount of ultraviolet (UV) light. Other than a possible link to eyestrain from long-term use, no health hazards are apparent. Most LCD monitors have a fluorescent backlight. Fluorescent lamps have the potential for some UV, but only if they're deliberately designed for it. UV emissions for LCDs are lower than CRTs.
Both LCD and CRT monitors emit some form of electromagnetic interference (EMI). Federal Communications Commission (FCC) regulations for computer equipment sold in the United States limit how much interference a monitor can make. These limits are low, but still detectable if you have the right equipment. The FCC limits are meant for practical use in home and office. Higher-priced monitors are available for specialty applications where interference must be as low as possible.
- Photo Credit dno1967, creativecommons.org
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