Dim light or cloudy days can lead to depression due to a lack of sufficient light activating melanopsin, and blue-shifted light in the morning may help with alertness and reduce depression.

“So, in dim environment, it becomes...means, many people know that dim light or cloudy days make us depressed, but now we have a molecular biology explanation why is that. At the same time, it also tells us maybe if we have blue-shifted light during the first half of the day that may help us to stay awake, to stay alert, and also to reduce depression.”