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It is a common belief that cacti absorb radiation; consequently, a lot of people put potted cacti by their computer as a safety means.

Do cacti actually absorb radiation? Even if so, will a small cactus (or several of them) by one's computer make any difference?

Some sources to prove this is a popular belief:

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A simpler answer would be "no harmful radiation is emitted by a computer." If it were, someone would have noticed and made it a regulated device and it is not. In the USA, there are FCC govt regulations limiting the amount of radio waves emitted by a computer or any other consumer devices, for interference purposes. The common manufacturing practice of enclosing the computer in a metal case that is then grounded limits this radio interference. –  Paul Mar 11 '12 at 8:31
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Also see this nice xkcd visualization of radiation sources –  David Mar 13 '12 at 16:21
    
@David: Nice one –  Armen Tsirunyan Mar 13 '12 at 16:54
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(Tongue firmly in cheek.) Well a screen does emit radiation in visible wavelengths. So one way to use a cactus for this purpose is to plant the cactus (a large one, that completely obscures the screen from view, maybe a full grown saguaro) immediately in front of the screen. Since this effectively prevents all use of the computer, the user will just power it down. No more radiation emitted by the screen. –  user3344 Apr 7 '12 at 9:09
    
@woodchips Of course the same goes for any other "harmful" radiation. Radiation travels in straight lines, so the only way this could work (and it doesn't, nor is there any need for it) is to surround the PC and monitor with cacti... –  hdhondt Sep 11 '12 at 0:08
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1 Answer

up vote 30 down vote accepted

The 'cactus absorb radiation' meme is very widespread, but seems very short on detailed analysis. So let's start with some basic facts.

  1. None of the articles are explicit about what radiation they are talking about. However the only significant radiation emitted by computer monitors is electromagnetic radiation, which for the most part is all around us all the time, and in general one of the least harmful kinds. Studies have shown again and again that radiation emitted from monitors is not a health problem under normal circumstances.
  2. Almost everything blocks electromagnetic radiation to some extent. Water and living tissue are good at it. Cacti do, but so do other plants; metal; plastic; clothes and water. Some of these are much better absorbers than plant tissue. There appears to be no evidence that cacti are better than other plants, for a given plant size. However thicker barriers absorb more than thinner; so cacti, being unusually thick plants, are probably slightly better than other plants (but worse than many other things). However even if this is true it is irrelevant because...
  3. Electromagnetic radiation travels only in straight lines. So any kind of radiation shield works only if it is sitting between you and the source of radiation. So even if it were good at absorbing radiation, for a cactus to be effective as a radiation shield it has to be large enough to fill the space between you and the monitor, an approach which would obviously make the monitor unusable. Having a small cactus sitting beside the monitor will do nothing.

In short: this is a complete fabrication, supported by a few misleading half-truths.

The only way a cactus will shield you from radiation is if you have a giant one between you and your monitor. Even then its effectiveness is doubtful.

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A search for ("nuclear cross section" "plant tissue" cactii) doesn't turn up much. google.com/… If cacti are good at absorbing radiation, I'd expect someone would have made a measurement to back up the claim. –  user951 Feb 27 '12 at 15:57
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I don't think cactus tissue is better for a given tissue size. Cacti are simply thicker than most plants. A single cactus will absorb more radiation than a single geranium, even if the tissue has the same absorbance. –  DJClayworth Feb 27 '12 at 15:59
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"Almost everything absorbs electromagnetic radiation to some extent.". You can remove the "almost". Everything will absorb some type of electromagnetic radiation. That is why, for instance, we see colors. –  nico Feb 29 '12 at 20:39
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Find me a cactus smaller than a wavelength of light and I will modify the answer. –  DJClayworth Apr 9 '12 at 22:56
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Another very important issue is that the visible light, the wanted product of computer monitors IS by itself EM radiation. Computer screens are omitting EM radiation because that is what there are used for! –  Ilya Melamed Apr 14 '12 at 13:55
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