On Saturday 31 March more than 2 million Sydney businesses and residents enjoyed Earth Hour, by turning off all of their lights and appliances between 7.30 p.m. and 8.30 p.m. Earth Hour signaled the start of a campaign that aims to reduce Sydney’s greenhouse gas emissions by 5% in 2007.

We enjoyed a great family time that night, and we all went to bed early (and happily).

Have you ever wondered how important light is to your state of mind?

Our brains respond to light and dark by ramping up or ramping down the activities of our vital bodily systems. Our bodies are designed to work in cycles of 24 hours, in tune with our natural world. If we don’t have our internal cycles matching our external ones, then psychologically and physiologically we are worse off. It is especially difficult to find a balance for people working shifts, airline staff and others with variable or unusual work hours.

Insufficient exposure to sunlight is a big contributor to the type of depression known as Seasonal Affective Disorder. SAD normally occurs in autumn and winter, with the shorter daylight hours. The most common treatment for SAD is light therapy, where the person spends a set amount of time each day, normally in the morning, sitting close to a special fluoroescent light device.

Some studies have shown that light therapy can help with the more common forms of depression, although the evidence is inconclusive. Irrespective of this, one of the easiest ways to lift your mood is to get exposure to natural light early in the day.

Why not try this easy experiment to see if it helps you?

• Set your alarm for a bit earlier in the morning than normal and spend some time outside

• Make sure that you enjoy at least 40 minutes outside during the day

• If you can manage some exercise at the same time then all the better

• Monitor your mood state over 3 weeks or more, and observe the changes. Hopefully you will have a new strategy that makes an big difference to you!