On the year’s longest day, around June 21, the Northern Hemisphere gets maximum daylight and the astronomical start of summer. In a Walla interview about sleep disorders, Professor Rivi Tauman explained that this extra light can delay the body’s sense that night has begun, pushing sleep later for many people.
She said the body follows an internal clock shaped by light, darkness and timing, not by the clock on a phone or wall. Morning and midday light help set the biological clock, while evening and nighttime light delays sleepiness. Melatonin, the hormone released mainly in darkness, is a key factor, and strong indoor lighting or screens in the evening can delay its release and keep the body in a daytime state longer.
Tauman pointed to 2023 research in the Journal of Pineal Research showing that daytime light exposure strongly predicts seasonal sleep timing, with people tending to fall asleep and wake later in brighter seasons. Another 2023 study found the circadian system is slightly less sensitive to light in summer than in winter, but longer daylight still pushes sleep later. People who naturally fall asleep late, or whose routines are disrupted by vacations, screen use or bright evening light, are especially likely to feel the effect.
The practical advice is to work with the body’s clock rather than against it. Natural morning light can help improve the following night’s sleep and move circadian timing earlier, while strong evening light, especially blue light from screens, can delay sleep and worsen sleep quality. Tauman recommended morning sunlight, less bright light and fewer screens in the hour or two before bed, and keeping the bedroom cool, quiet and dark. Dr. K. Elkra, a family physician with Maccabi Healthcare Services in the North District, was also identified in the piece.
