Monet’s paintings of the same scene, using his cataract-afflicted left eye (left) and his right eye with the lens removed (right).
… When he was 82 years old, Claude Monet suffered from such severe cataracts that he agreed to have the lens removed from his right eye. Cataracts that occur in elderly people turn the lens of the eye cloudy and yellowed, much like old glass can become discolored. The yellowing of the lens works as a filter, reducing the amount of blue light that reaches the retina. However, normal, healthy lenses filter out ultraviolet UV light, so when Monet’s lens was removed, he not only could see the blue hues again, he could also see a limited amount of UV—which he attempted to paint, as the images below demonstrate.
Visible light is a term relative to us humans: the combination of our crystalline lens and especially the cone cells on our retinas dictate what wavelengths of light we can perceive. That range of colors is relatively small compared to the entire spectrum of light, encompassing wavelengths from roughly 400 to 700 nanometers 0.0000004 to 0.0000007 meter , where the short wavelengths correspond to violet light and the longer wavelengths are red light. An average human can see light across these colors, but as the image at right shows, response by the cone cells isn’t perfect: some colors will show through more strongly than others. The brain takes electric signals produced by the cone cells and constructs the colors we perceive by combining the signals with their appropriate strengths. Note also that a little bit of UV light can sneak in, assuming the lens doesn’t block it; perhaps Monet’s retina was more sensitive to UV than average, though that sort of thing is hard to demonstrate. Human evolution has obviously selected for seeing this way; other animals don’t have equivalent vision.
Bees can see UV light but have less sensitivity to red light; some flower species have patterns only visible in the UV, indicating a certain amount of coevolution. After all, it takes “effort” in a certain sense to make patterns; if that effort isn’t rewarded by reproductive success, then the strain of plant bearing the pattern won’t make as many baby plants. Some species have more color receptors than humans do, and others have fewer. However, the range of vision in most species lingers around visible light, and that’s due to our Sun and Earth’s atmosphere. …