Weather forecasters in the United Kingdom use a sun index to warn of strong ultra-violet radiation. This index depends upon two factors: the position of the sun in the sky and the amount of cloud cover. The index simply refers numerically to the strength of the UVR. Individuals are then expected to take action to protect themselves, using four categories of skin colour as a guide: black skin; brown skin; white skin that tans easily; white skin that burns easily and tends not to tan. In the United Kingdom, a scale of one to ten is used for the index. Coupled with the scale, there are four categories of risk:
low; medium; high; very high. When the risk is low, the sun will not prove harmful. When it is medium, the sun is not dangerous but you should not expose yourself to direct sunlight for more than one or two hours. When the risk is high, you could burn in 30-60 minutes and you should wear sun-screen of SPF15. When it is very high, you could burn severely in 20-30 minutes. To all of the other consequences of over-exposure to the sun, we should add over-heating and dehydration.

Sunlight in moderation is good for us. It helps, for example, to ensure a correct vitamin balance in our bodies. Sunshine also makes us feel good. Not many people like cloudy, dismal weather.

Too much sun can be dangerous, for it may burn us. At the very least, we may become very sore if we stay out in the sun too long. Our skin may turn a bright red and then, later, peel. At worst, we may develop skin cancer, which can be a killer.

Black surfaces become hotter than white ones when the sun shines on them. Buildings in sunny climes therefore tend to be painted white, and many of the people who live in these parts of the world wear white clothes. Even in the British Isles, the ground can become hot on a sunny day. In the tropics and subtropics, where the sun is high in the sky around mid-day, the temperature of the ground, especially a road surface or sandy area, can exceed 70°C.

When the sun is low in the sky and the road wet, drivers may not be able to see where they are going. Consequently, accidents may happen. Drivers can also be blinded by sunlight reflected from the windows, mirrors and bodywork of cars.

Too much exposure to sunlight can be dangerous, because ultraviolet radiation from the sun can damage our skin. In the short term, we may suffer a painful sunburn. In the longer term, we may experience health problems of a serious nature. These include cataracts and other eye damage, skin cancer, suppression of the immune system and premature ageing of the skin. Children are particularly at risk of over-exposure, because most of the average person’s lifetime exposure occurs before the age of 18. Babies should be kept out of the sun completely.

To protect yourself, you should wear clothing that is tightly woven and loose-fitting. You should also wear a wide-brimmed hat that offers good protection to your ears, eyes and face and the back of your neck. Limit your time in the sun if you are going to be in it between 10am and 4pm. Seek shade whenever you can, but remember that ultra-violet radiation is reflected off light-coloured surfaces, especially water, sand and snow. Wear sunglasses that protect against UVR. Avoid artificial sources of UVR such as sun-beds, sunlamps, lasers and welding machines.

Remember you can get burnt when the sun is shining through thin cloud or a thin T-shirt. Remember, too, that droplets of water from swimming focus the sun’s rays on you.