Digital devices and cool light generally emit bright white or even blue light. These have been shown to disturb the secretion of melatonin – a hormone that controls the daily rhythm or circadian rhythm in each of us. This disturbs sleep patterns. So if you are looking for a peaceful, restful night of sleep, you may want to read a book in warm light (less white and more yellow) rather than use your digital device right until bedtime. You could even use a red night lamp – it has the least effect on sleep!