One topic that is often discussed when comparing CRT and LCD displays is that of safety. Although it is not directly connected to image quality, I’ll dwell upon it, too. And I’ll be talking about how dangerous CRT monitors are rather than about the safety of the LCD technology.
First of all, the monitor can be dangerous through radiation. I heard complaints that CRT monitors emit various types of radiation, from alpha particles to gamma radiation. Let’s browse through them one by one.
1) Alpha radiation is a stream of helium-4 nuclei. The cathode-ray tube has no helium to start with, so this radiation can only be the result of some nuclear reactions, which is absurd.
2) Next goes beta radiation, which is a stream of electrons. The cathode-ray tube does have a stream of electrons accelerated to energies of about 25,000 electron-volts (since the operational voltage of the kinescope is about 25 kilovolts), but there is one centimeter of glass between the electron stream and the user – no electron can break through it.
3) Hitting the phosphor, and being stopped by it, the electrons give only part of their energy to it (the phosphor shines due to this energy, by the way), while the remaining energy goes to the so-called bremsstrahlung (deceleration radiation), the radiation emitted by electrons slowed down in matter. The spectrum of the deceleration radiation stretches from zero to the maximum energy of the decelerating particles, i.e. its maximum energy may be 25 keV, which corresponds to very soft X rays (the term soft radiation is applied to a radiation with quantum energy up to a hundred thousand of electron-volts due to its relatively low penetrating property; for comparison, modern X-ray photography works with energies up to 150 keV).
4) Next to the X-ray radiation goes gamma radiation with quantum energies of tens of megaelectron-volts. It is created during nuclear fission reactions or as deceleration radiation when particles of energies of tens of MeV are being slowed down. Evidently, there are no nuclear reactions going on inside the monitor case, and there are no million-volt voltages in it, so it cannot emit gamma radiation.
So, the only type of radiation that may worry you is 3) soft X-ray radiation with an energy of about 25,000 electron-volts. To oppose it, the front glass of each cathode-ray tube (deceleration radiation is always directed forward, in the direction of movement of the particles it is created by) has lead and other metals (with lead alone, the glass eventually becomes blurry), which effectively stop this type of radiation. Thus, the X-ray radiation of the monitor originally has a very soft spectrum and after it has passed through the lead-doped glass of the tube it doesn’t exceed the natural background radiation.