The human brain appears to be, per se, sensitive to light.
Light-sensitive brain neurons
Researchers at the University of California Los Angeles (UCLA) have identified a group of neurons that arouse us when there is light.
The light-sensitive cells in question are found in the hypothalamus, an area at the base of the brain responsible for sleep and also other things like controlling the autonomic nervous system, body temperature, hunger, thirst, and fatigue.
Optogenetics, a technique developed over the past 15 years, has become a common laboratory tool for shutting off or stimulating specific types of neurons in the brain, allowing neuroscientists to learn much more about their functions.
Light’s action on non-image-forming brain functions
Notwithstanding its effects on the classical visual system allowing image formation, light acts upon several non-image-forming (NIF) functions including body temperature, hormonal secretions, sleep-wake cycle, alertness, and cognitive performance.
Human brain broadly sensitive to light
Their research localized the OPN3 protein – known as the light-sensitive photoreceptor protein – in all of the 18 evaluated areas of the brain. These brain areas include the core areas of serotonin and melatonin production and storage, which play key roles in mood, sleep and depression. The study shows that the human brain is sensitive to light also outside of the visual system.