Prof. Damien Léger, Head of Sleep Centre, Hotel-Dieu Hospital, Paris, "When you are exposed enough, especially in the morning, to daylight or a day light-type of lamp when you don’t have enough day light, well it's enough to resynchronize your clock."Technically, light goes through the retina nerves and affects the secretion of melatonin a hormone that synchronizes sleep. Used well, it can also help you feel more awake. And it's catching during the winter gloom. In this shop, sales have gone up 20 percent every year for the last two years.