My guitar teacher once told me that leaving a magnet near a LCD screen will affect it. I was skeptical because I guess that he believes that because magnets can affect CRT screens.

Here are some examples of others making this claim:

Is there any evidence to suggest that this may be true?

  • CRT screens are definitively affected affected by magnetic fields which was the whole reason for degaussing. – rjzii May 14 '12 at 5:24
  • The second link actually makes contrary claim: "the effect of a magnetic field on an LCD/LED monitor is generally unnoticeable" – vartec May 14 '12 at 12:39
  • There is one component in some LCD screens where electron movement matters and (plausibly) might be affected by magnetic fields too weak to affect solid-state semiconductors: the backlights. Some LCDs and most older LCDs use cold cathode compact fluorescent lamps (CCFL) backlights. These are high-voltage, high frequency discharge tubes involving electron discharge as a means of generating UV light. Magnets could plausibly interfere with this in ways that might damage operation (and I did once wreck a screen backlight with a magnet, maybe). – matt_black May 14 '12 at 12:40
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    Related: superuser.com/q/113430/334004 (the second answer) – Cornelius Oct 24 '14 at 13:13

Magnets affect electrons only when they are moving. The force on an electron in a magnetic field is proportional to its speed. If it is stationary, the force is zero. In LCD screens there are no moving electrons, except when the image changes, so there cannot be any effect with a steady display. Any effect during a moving display will be very small (because the electrons in and LCD cannot drift as they can in a CRT), and will disappear once the display is steady again.

The other problem with CRTs is that they can become permanently magnetised, and thus always affect electrons as they fly to the screen. That is why CRTs sometimes need to be de-gaussed. In LCDs there is nothing to magnetise (and no flying electrons) so this effect is also negligible.

Also, I noticed that both your links point out that LCDs will not be affected by magnetic fields (actually the Win 7 link says that any effect is too minor to be visible).

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    Hi hdhondt, Welcome to Skeptics.SE! Here we require all ansers to be suitably referenced to ensure the quality of answers is consistent. Would you be able to find some references to add to your answer? – Sonny Ordell May 14 '12 at 12:43
  • @Sonny I've added some more explanation, as well as a few references. – hdhondt May 15 '12 at 2:41
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    It's actually incorrect to state that "Magnets affect electrons only when they are moving". Variable magnetic fields will affect static charges. Also, what about any metallic parts that can be affected? LCDs have way more electronics than CRTs... The question is "what will happen in practice?" and most definitely not "what will happen theoretically?" – Sklivvz May 15 '12 at 22:56
  • Electrons are always in motion. There will always be a certain amount of non-zero kinetic energy associated with an electron. In fact, all atoms and molecules are always in motion, even at absolute zero (termed zero-point energy), further reinforcing the fact that electrons are always in motion. What do you mean by 'movement'? Electron transfer between atoms or molecules? Electronic excitations? In addition, magnetic fields will always affect electron density. This is a simple application of Coulomb's law and electrostatic interactions. – LordStryker Oct 24 '14 at 14:43
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    @pacoverflow That must be a coincidence, since an iPad certainly doesn't have a CRT display. I wonder if the magnet was actually warping the housing slightly and that caused the LCD to discolor. I wasn't able to repeat the effect by holding a similar magnet up to an LCD monitor. – user45623 Feb 3 '17 at 2:18

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