Roger Seheult, MD
Light before you wake up is used by your body to prepare for waking with many studies showing the benefit with strength, cognition, and alertness. Light immediately after you arise is used to strengthen your circadian rhythm for the rest of the day and set up melatonin 14 hours later for a better night's sleep. Both of the above go away when the sun rises after you wake up. pDST makes this much more likely precisely during the months when we have a scarcity of sunlight to being with.