Life has evolved for several billion years with a reliable cycle of bright light from the Sun during the day, and darkness at night. This has led to the development of an innate circadian rhythm in our physiology; that circadian rhythm depends on the solar cycle of night and day to maintain its precision. During the night, beginning at about sunset, body temperature drops, metabolism slows, hunger abates, sleepiness increases, and the hormone melatonin rises dramatically in the blood. This natural physiological transition to night is of ancient origin, and melatonin is crucial for the transition to proceed as it should.
Evidence suggests that circadian disruption from over-lighting the night could be related to risk of obesity and depression as well. In fact, it might be that virtually all aspects of health and wellbeing are dependent to one extent or another on a synchronised circadian rhythmicity, with a natural cycle of bright days and dark nights.
LED technology is not the problem, per se. In fact, LED will probably be a large part of the solution because of its versatility. The issue in street lighting is that the particular products being pushed by utility companies are very strong in the blue – and they don’t have to be. Different LED products can be marketed that are much more friendly to the environment and our circadian health. This is of paramount importance when lighting the inside of buildings where we live and work.