Sun and Health

Negative Health Effects of Sunlight

The sun brings warmth, light and life – so it’s often been thought of as a god. Ancient cultures worshipped the sun, offering food and even human sacrifices in religious ceremonies to keep the god happy. Most of the time the deity obliged and regularly drove across the sky in his or her golden chariot. Our ancestors, however, could be quite naughty at times. At quite regular intervals, when the fruit and vegetables or attractive young human just weren’t good enough, the god turned black in anger, was eclipsed or darkened the sky.

sun-450x450Not much has changed since then. Today, millions of people worship the sun – especially during school holidays. They flock to the beaches and stay at the foreshore temples. In the morning they pray for sunshine and curse every tiny cloud. They lay out their near-naked bodies on top of ceremonial towels and offer their health and sometimes their lives to the sun. In return, the sun turns white skin to bronze and presents everybody with a free dose of vitamin D.

Who is this sun god? It is a giant ball of glowing hydrogen and helium, ignited just under 5 billion years ago. By the way, the word ‘helium’ comes from the Greek word helios and stands for ‘sun.’ The earth just happens to circle the sun at a safe distance to avoid the scorching heat, but close enough to deny any frost permanent residency in most of the earth’s regions. The glowing gases of the sun reach temperatures of around 5,500°C at the surface – certainly an efficient space heater for your family room and no gas bills for another 5 billion years. Of course it wouldn’t fit:  being 1,392,000km in diameter, the sun is about 109 times the size of the earth.

The sun’s heat also drives the weather. The rays heat a variety of the earth’s surfaces to different temperatures and also the air above. The air over a warm patch rises and leaves an area of low pressure near the surface. Cooler air from the relatively high pressure in the neighborhood eventually replaces the risen air and fills the low. The action of replacement, whether small scale or global, is the wind, while the border between the cooler and warmer air is called a front. The sun’s heat also evaporates water. The wind carries the water vapor into the atmosphere where it may condense and create clouds or rain.

Visible sunlight is the first thing you notice when the sun rises. The warmth of the infrared rays is probably next. But these are not the only components of electromagnetic waves originating from the sun. The known forms include rays with very short wavelengths, such gamma rays and X-rays. At the same time, the sun sends out slightly longer waves in the visible and non-visible light range: ultraviolet, visible and infrared light. The spectrum also includes microwaves, radio waves, electric and long waves.

Visible Light Spectrum

Colour is perception. The green traffic light is only green because you were told as a child that the colour you see is green. The Woman in Red looks absolutely gorgeous in her red dress. Does she? Many people have colour blindness and aren’t aware of it. To them the red dress is just another shade of grey.

Visible light is nothing other than a package of electromagnetic waves with very short wavelengths of between 400 and 700 nanometres (1nm = 10-9metre). When the eyes receive the whole package, you see it as white light. Sometimes substances break the package and send the waves individually to your eyes. Raindrops do so when the sun is at a certain angle, and break the light into the colours of the rainbow.

The fabric of the red dress reflects only the longer wavelengths of the light: around 700nm. A violet-coloured dress reflects light with the shortest visible wavelengths: approximately 400nm. All other colours are at wavelengths in-between. To be thoroughly accurate, you may as well rename the previously mentioned song title to The Woman Wearing a Dress Reflecting Light with a Wavelength of 700nm.

With the exception of deep-sea and underground creatures or plants, most life forms depend on the visible light in some form or another. Light gives you the chance to enjoy your surroundings. It gives you vision. But light is also a life clock that controls the day and night cycle in plants, animals and humans. It reminds you when to wake and sleep cycle (circadian rhythms). The level of light intensity sensed by your eyes affects the amount of melatonin released by the pineal gland. Melatonin is a hormone thought to influence the circadian rhythm. Jet lag and sleep disorders are the consequences when this rhythm is out of sync.

Plants, animals and humans detect seasonal changes in light intensity. Light activates the need to breed, hibernate or migrate in some animals. It triggers plant seeds to germinate and flowers to open. Shorter daylight hours bring about the ‘winter blues’ in some people and may even develop into serious depressions (Seasonal Affective Disorder, or SAD).

Scientists are now assessing whether the present artificial lighting in homes, offices, schools etc. is impacting negatively on our performance, mood and health. They argue and test the possibility that humans require the whole spectrum of light to function properly. Most modern artificial light sources radiate only part of the spectrum.

Arguably the most important function of light is to provide food. You need sunlight in order to have your evening meal – not to find the steak or carrot on your plate, but to have the food there in the first place. The plants draw water from the ground and store it in their leaves. The light energy splits the water molecules into hydrogen and oxygen atoms. Hydrogen then combines with carbon dioxide to create a form of sugar. The leftover oxygen is released into the atmosphere for your benefit. By this chemical process, called photosynthesis, the plant becomes either a direct food source for you in the form of fruit or vegetables; or is an indirect food source in the form of meat, milk or egg from the animal that beat you to the lettuce.

Comments are closed