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It is known that high exposure to radio waves, microwaves, ultraviolet, x-ray, and gamma ray can all negatively affect you. I wonder if being exposed to visible light all the time can have a negative effect on the human body. Can you please give me some answers or comments?

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closed as off-topic by ACuriousMind Jul 4 at 17:36

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    $\begingroup$ Generally, EM radiation of any wavelength can cause damage at least by thermal effect, if it is absorbed. $\endgroup$ – Poutnik Jul 4 at 5:43
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    $\begingroup$ I'm voting to close this question as off-topic because it is about the biological effect of radiation on the human body, not physics. $\endgroup$ – ACuriousMind Jul 4 at 17:36
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Any form of energy, in enough quantity and delivered fast enough, can be dangerous, even lethal - although some forms are considerably more dangerous than others in terms of damage dealt per joule absorbed, e.g. ionizing radiation like X- and gamma rays.

The chief method by which visible light can cause injury is through being absorbed and turned into heat. Unlike microwaves or RF radiation, however, visible light does not heat deeply, but rather at the surface of tissues. In this regard, it has essentially the same effects as infrared light: indeed, roughly 30-40% or so of the "heat" that you feel on a sunny day is actually delivered by the visible light, while the rest is delivered by infrared (UV is only a small component). Hence, at high enough intensity (radiant heat guidelines like those at: suggest around 10 $\mathrm{kW/m^2}$), both visible and infrared radiation can cause injury by thermal burns. Such intensities can be generated from sources such as fires, lasers, and nuclear weapons.

The reason we typically associate infrared, and not visible, with "heat" is because common "hot-feeling" sources emit far more copious quantities of it than common "visible" sources emit visible light, with the possible exception of the Sun as just mentioned, and that is because both visible light is relatively high in energy, so requiring a very high emission temperature (the Sun has a surface temp of ~5800 K), and also that our eyes are quite sensitive, so it takes surprisingly little power to make them notice, while our skin doesn't register a sensation of heat until considerably higher power levels. For example, a hot stove (I'm thinking of an old wood stove here, fired up, because it's both hot and big so lots of power output) with a surface at 600 K emits on the order of $7\ \mathrm{kW/m^2}$ in terms of thermal radiation of which virtually all is infrared. Were this a visible light source instead, it would be blinding: a typical LED lamp, suitable to light a room, may only put out 5-10 W of visible light and for typical sizes, just by eyeballing the surface area, a stove-equivalent visible source would easily put out 30 kW or more of total radiated energy, up to 6000 times more brilliant. Hence, you do not typically feel heat from the lamps emitting visible, but definitely do from the stove.

If the stove were emitting visible, though, you would feel it as heat just same, but you wouldn't dare want to have your eyes exposed.

And eye damage, too, is mostly a heating effect: intense visible sources like lasers chiefly damage the eyes more easily than they damage skin (a 100 mW laser can easily blind, but it takes maybe 4000 mW (4 W) or more to start hurting skin) because the eye has the ability to focus them down to a tiny, super-hot point on the retina, effectively acting like a surgical drill that cuts right through the delicate tissues or, at the very least, cauterizes them and leaves a permanent scar.

(It's also worth pointing out that long-term eye exposure to intense infrared radiation, like that emitted from hot metal-shaping furnaces, even if not enough to cause immediate burns, can cause a sort of progressive damage, but not due to exposing the retina so much as due to heating up the cornea and lens, which are not very good at getting rid of heat yet very absorptive thanks to the water absorption band that kicks in around 1550 nm. Such chronic heating can promote the formation of cataracts "down the road" and thus, if one is spending or will spend significant amounts of time engaged in activities involving heavy or consistent exposure to such like blast furnace operation or glassblowing, one would be well advised to acquire a pair of infrared-blocking safety goggles if one does not have them already.)

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Too much visible light can be blinding. There are various articles online that say blue light can be damaging to eye health in the long run. Which makes sense since it's the higher energy visible light.

This article brings up possible skin damage

https://www.ncbi.nlm.nih.gov/pubmed/18248499

Visible light is generally non-ionizing radiation. Wikipedia says the upper frequencies can still cause some biological damage similar to ionizing radiation though.

https://en.wikipedia.org/wiki/Non-ionizing_radiation

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  • $\begingroup$ How does it affect our body (other than our eyes), such as too much UV can cause skin cancer, and too much microwaves can cause burns? $\endgroup$ – Michael Wang Jul 4 at 5:24
  • $\begingroup$ Too much visible light makes burns as well. Most children know that focusing light by a lense burns you and can put matter in fire. $\endgroup$ – Poutnik Jul 4 at 5:44
  • $\begingroup$ @Poutnik I believe the visible light has to be focused at a point to burn stuff. $\endgroup$ – Michael Wang Jul 4 at 5:48
  • $\begingroup$ Have I mentioned focusing ? $\endgroup$ – Poutnik Jul 4 at 5:49
  • $\begingroup$ The same radiation absorption rate in W/g is about the same harmful in range of visible (or rather red side of) light to radio waves. Impact of the same irradiation is affected by the absorption path. $\endgroup$ – Poutnik Jul 4 at 5:55

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