The use of light as a therapeutic tool has a long history, with reports of sunlight being used to treat depression and lethargy over 2000 years ago in ancient Greece and Rome. The use of light in therapy today however stems largely from research carried out in the 1980s that looked at the cycle of depression, and other problems, associated with changes in the seasons of the year.

Many of the body's functions are regulated by an internal clock which operates on a pattern that repeats roughly every 24 hours and that gives a rhythm to our lives. Indeed, this is often referred to as the body's circadian rhythm, from the Latin 'circa dies' meaning 'about a day'.

Unlike your kitchen clock or wrist watch, however, which are more often than not powered by batteries these days, your body clock is essentially a chemical clock and is powered by a variety of different environmental factors, the most significant of which is the alternating pattern between daylight to darkness.

In simple terms, as your body senses the fall of darkness it sends out signals, shutting down many of your body's functions in preparation for sleep. Similarly, as daylight returns, signals are again sent out for these same functions to start up again.

So just how can we apply this knowledge to the treatment of insomnia?

There are three main types of insomnia