[mapt]

"infrared" is actually an extremely large portion of the spectrum when viewed on a proper log scale. It's a poor label because it often leads to this confusion.

400nm to 700nm is 'visible light', a factor of 1.75x, infrared is 700nm to 1mm, a factor of 1428x.

Only a small portion of this is significant for thermal infrared applications, which at room temperatures are about 8um-15um.

Near infrared, up to about 1500nm, acts pretty much like light we can't see, and can be detected well on the same CCD/CMOS sensors (which need filters to block it out).