Human beings and light

Light is life. The first life on Earth developed three billion years ago with the help of the sun. Homo sapiens has been around for about 170,000 years. For much of that time, all he had to dispel the darkness was fire. Electric light has been in use for a little over 100 years. 

The discovery of the third photoreceptor in the eye at the beginning of the 21st century confirmed what scientists had long suspected: light does more than just enable us to see; it also plays an important role in synchronising our biological clock. Light has a lot to do with whether we are alert, rested and dynamic, whether we sleep well and feel fit and healthy