Many religions have festivals at this time of year involving lights, Diwali, Chanukah and Christmas among them and while we try to make the season bright by dressing trees with strings of lights and by lighting candles, outside it's getting darker and darker.

At the winter solstice, sunlight in the Northern Hemisphere is the shortest and dimmest of the year. The next few months will remain dark even as daylight begins to increase. The lack of daylight is especially obvious for people who wake up before sunrise in winter and leave work after sunset. Once all the bustle, shopping and visiting and especially the lights of December are over, the darkness really seems to set in. Millions of people suffer from a biologically based depression during this period known as Seasonal Affective Disorder or S.A.D.  

Although these people may feel fine during the spring and summer, autumn and winter are an entirely different experience. As well as the depressed mood, seasonal affective disorder often brings a loss of interest or pleasure in everyday activities that are normally satisfying, such reading a good book or listening to music. Other common problems are a significant reduction in work productivity and withdrawal from friends and family that is hard to explain or justify. 

Craving for carbohydrates is another common feature, especially during the evening in an attempt to overcome the low mood. And it's not just at this time of the year that we notice the effects of the lack of light.  Research shows that over the last half of the 20th Century sunlight reaching the earth has reduced by as much as 2-3% per decade.  This is attracting scientific attention with implications for weather, water and agriculture - but what about people? 

As more offices are now being built with tinted glass and low levels of lighting with pools of brighter 'task' lighting.  Lack of light can cause loss of energy and can exacerbate the symptoms of S.A.D. The only glimmer of hope in this landscape is the '30 St Mary Axe' designed by the renown architect, Sir Norman Foster.  The key to the design of this particular building was the availability of natural light, with the offices arranged around the outside of the structure. More people are also experiencing sleep problems. 

The Zeitgebers we had previously are no longer defined as they once were causing an imbalance in the circadian rhythms.  These Zeitebers are an environmental agent or event that provides the cue for setting or resetting a biological clock. To be synchronized with our environment, we need the input of Zeitebers, This is caused by not getting the amount of sunlight that we have had in the past during the day and with light pollution there is not complete darkness at night.  

So Why Are These Light Cue's So Important?
Light and of the right intensity when we wake up stops the production of the hormone melatonin which is what makes us sleepy and lethargic and make animals hibernate and encourages the production of serotonin the 'feel good' hormone.  

Conversely we also need complete darkness at night to encourage the production of melatonin and a good night's sleep. Extensive research over the past 20 years has shown that bright light therapy helps.