The evolution of life on this planet is largely due to the suns' continuous supply of radiation. Over many thousands of years, animals and humans have become attuned to the Earths' seasons and cycles, and to the intensity and availability of sunlight through these cycles. Before the days of electric lighting, humans lived their lives by these patterns, working while there was light, and resting when it became dark.

This attunement can be seen now by observing and comparing our moods during the day (when we are active and energetic) and in the evening (when we slow down and need to sleep), and during the summer and winter months. In the winter, with its short, grey days, we are more sluggish and depressed than in the summer with its long sunny days, when we are more energetic and generally happier. This is partly due to, in temperate regions, the sun being one tenth of its summer intensity during the winter months. This causes significant changes to our hormone levels, in particular, that of the hormone Melatonin, secreted by the pineal gland during hours of darkness. Overproduction of this hormone can lead to Seasonal Affective Disorder, or SAD, also known as winter depression. (For more information about SAD, read our article, "Seasonal Affective Disorder".)

These days we can manipulate the length of our working day by the use of artifical lighting. We are no longer in tune with the planets' seasons and cycles, and this may have an adverse affect on our health. Added to this, many of these artificial lights are of the harsh, shadowless office type that only give part of the natural spectrum of light. Experiments with animals and humans have shown this can have an adverse effect on health.

The natural conclusion we can draw from this shows that the way we light our surroundings can be important to our health and well-being. Daylight is an important feature of any home or working environment. Increasing the amount of daylight improves your health and reduces your reliance on expensive artificial light.

You can make a number of changes to your surroundings to increase the penetration of daylight in your home, such as:

• Keeping the windows clean
• Drawing the curtains fully back
• Laying light-coloured paving underneath windows to reflect light indoors
• Painting walls and fences opposite windows a light colour for the same reason
• Cutting back overshadowing trees and plants
• Raising the height of the windows (this is more effective than widening them because you get more sky area)
• Installing rooflights and skylights
• Installing a 'light tube' (which brings natural daylight from the roof down a reflective tube)
• Growing only deciduous trees, bushes and climbers near the house to allow in more of the winter sun

You can also increase the reflection of daylight from interior surfaces by:

• Using light-coloured decorations, furnishings, and carpets
• Painting the walls a light colour
• Using mirrors to reflect light around a room

You can also use full-spectrum lamps to mimic sunlight during hours of darkness. These come as incandescent and fluorescent lamps and are designed to closely replicate the colour spectrum of natural daylight. They also give a slightly higher level of UV light than ordinary lamps.