Now the mystery has been solved.
Now researchers have figured out why: a light-sensitive protein called rhodopsin interacts with a photosensitive compound called chlorin e6, a component of this type of cancer treatment.
It’s all about an organic compound called retinal, which is found in the eye and usually isn’t sensitive to infrared light.
Visible light triggers retinal to separate from rhodopsin, and this is converted into the electrical signal our brains interpret to see. We don’t get much visible light at night, but it turns out this mechanism can also be triggered with another combination of light and chemistry.
Under infrared light and with a chlorin injection, retinal changes in the same way as it does under visible light.
“This explains the increase in night-time visual acuity,” according to chemist Antonio Monari of the University of Lorraine in France.