Are there circumstances where we can perceive spectra outside of the visible band with our eyes? When you point a remote control at a receiver it's supposedly an infrared wave but you can see it glow red. Is this because part of the signal being sent lies in the red visible spectrum, or is this due to something else?
^^ I found some interesting info online about your first question regarding circumstances where humans can perceive spectra outside the band we usually define as being visible:
"While most of us are limited to the visible spectrum, people with a condition called aphakia possess ultraviolet vision. Aphakia is the lack of a lens, due to surgical removal for cataracts or congenital defects. The lens normally blocks ultraviolet light, so without it, people are able to see beyond the visible spectrum and perceive wavelengths up to about 300 nanometres as having a blue-white colour.
A study in 2014 pointed out that, in a manner of speaking, we all can see infrared photons, too. If two infrared photons smack into a retinal cell nearly simultaneously, their energy can combine, converting them from an invisible wavelength of, say, 1000 nanometres to a visible 500 nanometres (a cool green to most eyes). " The article goes on: http://www.bbc.com/future/story/20150727-what-are-the-limits-of-human-vision
There are also researches focused on whether it is possible to implant more color cones to human eyes so we can see IR or UV in the future. More importantly, we can implant cones to the colorblind so they can actually start to see more colors!
Adding to the discussion above. Although not an innate ability of our eyes, it is noteworthy that we have technology able to convert much of these wavelengths or magnify them to a point of visibility. For example, night-time goggles and infared vision.
There are also animals that can see light outside the "visible spectrum" of human. For example, snakes can see infrared light.
I believe researchers have successfully developed electronic devices that allow blind people to regain vision through their tongue: https://www.newyorker.com/magazine/2017/05/15/seeing-with-your-tongue
I saw online that there's an interesting chart with devices according to the certain range of light here: http://cmb.physics.wisc.edu/pub/tutorial/spectrum.html
Also, as a side note, the reason that we are able to see this band on EM is because it is actually that the radiation by the sun that is the most intense. The intensity of the radiation is affected by our planet’s distance from sun, our atmosphere, the suspended particles acting as pollutants etc . . .
Is it ever possible to see the "invisible" colors?