The findings from biologists at John Hopkins University could have implications for people suffering from seasonal affective disorder and insomnia, the university said in a release.
"It seems that even if individuals have normal sight, they might be having a malfunction that is contributing to their inability to detect light, which can adversely affect their biological clocks," said Samer Hattar, an assistant professor of biology.
The study, published online in the journal Nature, said tests on mice showed that there are two distinct pathways for the two different aspects of light detection -- image-forming and non-image-forming.
Hattar and his team said daily exposure to natural light enhances memory, mood and learning. He said people should get out in the sun for at least a little while each day and avoid very bright lights at night.
"The idea is to keep your internal rhythm in sync with the cycle of the sun: exposure during the day when the sun is out, less exposure at night, when the sun is down, so to speak," Hattar said.