I was thinking of the mold issue of floppies and UV light (UV-C) came to mind. As ultraviolet (UV) is a form of electromagnetic radiation and floppies use a magnetic disk for storage and I vaguely remember something about tapes that should not be exposed to direct light.

floppy mold

What is the effect direct exposure of magnetic disk of a floppy to UV light? Is there a difference to the specific UV-A, UV-B and UV-C? Will it just wipe the data from the disk or will is physically damage the disk or coating on the disk? How long should the disk be exposed to be disinfected using UV-C and also, how long will it take for potential damage to the magnetic disk occur when exposed to UV?

Lastly, because I recently watched the Vertasium video about UV (https://www.youtube.com/watch?v=V9K6gjR07Po), how would a floppy or other similar magnetic disk (storage tape) look in UV light?

floppy parts

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    I don't know if there will turn out to be magic physics re UV and magnetic domains, but almost all polymers react badly to UV. I would imagine the disk would probably disintegrate with all bits intact before spooky electromagnetism.
    – Dan
    Jan 2, 2022 at 0:08
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    yep it degrades the plastic material long before any electro magnetic issue might happen ... IIRC on top of mechanical damage UV might also alter the chemical composition of the plastic (and not just the plastic)
    – Spektre
    Jan 2, 2022 at 6:18
  • @Spektre how will it degrade the plastic? After what intensity and duration of exposure? Is the effect the same for all magnetic disks or for specific models? Will it damage the disk coating only or the actual plastic?
    – Bob Ortiz
    Jan 2, 2022 at 13:46
  • @BobOrtiz no expert on the matter but UV is like mechanical bombardment that causes surface damage on most materials, on top of this plastic polymers might dissolve to less complex molecules all this resulsts in worsening of mechanical properties of the disc (causing surface defects, brittleness, lost of color). My understanding is that exposure is cumulative so there is not a low limit on intensity , but frequency of the light the higher frequency the bigger energy once you are above molecular bond energies (on impact) even single photon is enough. Too high energy photons can also cascade ...
    – Spektre
    Jan 3, 2022 at 5:43
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    the effect depends on molecular structure and if UV protective coating is present ... For parts inside cover is usually no UV coating used so I doubt any vendor would use them for the disc surfaces ... However different vendors might use different polymers and that might be a difference
    – Spektre
    Jan 3, 2022 at 5:51

1 Answer 1


UV light won't affect the magnetic signal.

It will however degrade most plastics. UV has energetic photons, that can break apart the molecules in the plastic, thereby degrading it. This has nothing to do with the magnetic information; merely the fact that the plastic will become brittle dust over time.

  • @vidaelo I don't know enough about this subject but can you explain why UV light does not affect the magnetic signal? The reason this came to mind is that UV light is in the electromagnetic magnetic spectrum.
    – Bob Ortiz
    Jan 3, 2022 at 10:23
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    @BobOrtiz UV light induced currents are too small (really just an occasional ion) to generate non-negliggible magnetic fields... the remagnetization from the neighboaring tracks are huge in comparison ... The only magnetism related effect of UV I can think of is absorbtion creating heat and passing Currie temperature but the plastic would probably melt/burn before that happens and also it would require quite a powerful UV source...
    – Spektre
    Jan 3, 2022 at 13:50
  • @Spektre Thanks a lot. I think that should be part of your answer :).
    – Bob Ortiz
    Jan 3, 2022 at 15:48

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