Human visual sensitivity is primarily in the green and yellow part of the spectrum (photopic sensitivity curve). Light below 500 nm has a limited usefulness to the human eye. "Blue light has a greater tendency to affect living organisms through disruption of their biological processes that rely upon natural cycles of daylight and darkness, such as the circadian rhythm."

"Looking up at the blue sky has twice the resetting effect on our circadian clocks as looking down at green grass."