Will a bright infrared light damage your eyes if you look at it too much?

Question

even if you don't know you're looking at one?

Answer 1

I doubt it.  The photons just aren't very energetic.

Answer 2

Oh no.  Please don't listen to these people.  Yes, absolutely you can hurt your eyes looking at an IR light.  And if you were looking at one, you would not know that you are looking at it since it's invisible to you.  

Of course, it depends on what wavelength of IR you are talking about.  The near IR (800 nm to 1400 nm) is focused on your retina just as if it were visible light.  The only difference is your retina does not have receptors that detect it.  If you look at a visible light that is too powerful, you will damage your eyes.  If you look at a IR light in this range that is equally powerful, you will do nearly equal damage.  And you do not have pain receptors on your retina to know you are burning it.  Because you don't detect it, so you wont blink or look away like you would with visible light, IR light in this range is actually more dangerous than visible light.  It does not matter that the photons are less energetic, since when you talk about light power, you talk about total energy and not energy per photon.

If you look at light over 1400 nm, it will be absorbed primarily by your cornea.  Since it is not focused by the lens (like the near IR is), it is much harder to get the energy density needed to damage your eye.  Also, you can sense pain in your cornea, so you will know that your eye is getting burnt.  And the cornea is one of the fastest regenerating tissues in your body, so damage to the cornea is not as catastrophic as damage to the retina.  So, unless you are looking at a super powerful light source in this range, it's probably not a concern.  They do, however, make lasers that are plenty powerful enough at these wavelengths to do damage.

In general, it is hard to find light sources in the IR that are powerful enough to do damage, in either wavelength range.  Diffuse sources, like the ones used to heat things, are not going to be powerful enough.  And things in consumer products (laser mice, remote controls, etc) are going to be made weak enough to not cause damage for legal reasons.  But if you are talking about IR lasers or powerful night illumination systems, eye damage is certainly an issue and IR lasers cause more laser eye injuries than all other types of lasers.

Answer 3

Infrared light is invisible and is used in heat lamps (you can see the infrared light bulb filament glow).  Likely you would be aware of the heat from the source if it is strong enough to bother your eyes.  UV light (also invisible ) has shorter more penetrating rays that can cause sunburns and harm eyes.  The much shorter infrared rays are less powerful.