Any science textbook will tell you we can’t see infrared light.
Like X-rays and radio waves, infrared light waves are outside the visual
spectrum.
But an international team of researchers co-led by
scientists at Washington University School of Medicine in St. Louis has found
that under certain conditions, the retina can sense infrared light after all.
Using cells from the retinas of mice and people, and
powerful lasers that emit pulses of infrared light, the researchers found that
when laser light pulses rapidly, light-sensing cells in the retina sometimes
get a double hit of infrared energy. When that happens, the eye is able to
detect light that falls outside the visible spectrum.