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Ultraviolet radiation

Of all radiation from the sun, the ultraviolet (UV) end of the electromagnetic spectrum has the most significant effects on your health. At low levels of exposure it can be beneficial, but exposure to high levels for long periods can result in premature aging of the skin, melanoma, and eye damage. But there is no real agreement among medical experts on where to draw the line between healthy and hazardous exposure to UV radiation, mainly because so much depends on the type of skin you have (light or dark), climate, altitude, the amount of time you spend in the sun, and your age (children being more susceptible).

One thing researchers are agreed on, however, is that the depletion of the ozone layer, which shields the planet from the worst effects of UV, will allow more of the highest-energy radiation (UV-C) to penetrate. Thus, both moderation and proper protection are thought to be even more essential than ever before.

At present, the construction of our homes and the use of ordinary glass shield us from current levels of lower- energy UV-A and UV-B. But windows and skylights made of certain plastics, such as polycarbonate and acrylic, do not. When these are used, as is often the case in mobile homes or as sheeting to cover home extensions (sunlounges or greenhouses), UV radiation will penetrate. In sun-deprived areas this can be beneficial for occasional sunbathing, but you need to take care, particularly in summer, if you sit for long periods by these plastic windows and skylights. UV radiation can also cause the deterioration of and off gassing from furnishings and curtains, especially if they are made of synthetic fibres. Full- spectrum lamps also emit small amounts of UV.

Full-spectrum lamps

These light sources are produced in the form of incandescent bulbs and fluorescent tubes for general interior lighting. They are designed to replicate moreclosely the spectral balance of daylight and they emit slightly higher levels of UV than ordinary bulbs and tubes. Manufacturers of full-spectrum lamps claim that their products are beneficial if you are sunlight deficient, improving your mood and performance. But with the increased concern about UV and as yet no satisfactory medical definition of safe levels, caution is advisable. In the US, these lamps cannot be advertised as health products.

In some offices, full-spectrum lamps have been overused and have had to be changed because the increased level of UV reacted with hydrocarbon pollutants in the air to produce a photochemical smog.

PCBs and other pollutants

Many older fluorescent fittings have starting devices, known as rapid-start ballasts, containing highly toxic polychlorinated biphenyls (PCBs). These starting devices can leak and produce high concentrations of PCBs in rooms where this older type of fluorescent lighting is installed (usually kitchens and bathrooms). As a precaution, check the age of any fluorescent fittings you have in your home. Even if you cannot be certain of their age, it is safest to replace them, preferably with incandescent lights.

Bear in mind, however, mat the most common incandescent lamps become hot when in use and they can cause plastics and paints in or around the fittings and shades to vaporize and pollute the air. The heat produced also disturbs dust and this, together with other indoor airborne pollutants, can act as irritants and cause allergic reactions.

Fluorescent lighting and stress

Although fluorescents are energy efficient, many people report symptoms of irritability, eyestrain, headaches, allergies, and hyperactivity when working by fluorescent lighting. Flicker, hum, glare, and UV all cause problems. The flicker you sometimes notice with fluorescent lighting occurs at a rate of either 50 or 60 cycles per second (depending on your electricity supply). This means that the tube is effectively switched on and off 100 or 120 times every second. Although it is supposed to be imperceptible when the light is functioning properly, with old or malfunctioning lights the flicker becomes distressing (as does the associated hum).

New fluorescent tubes have been designed to accelerate this cycle up to a thousand times. Manufacturers claim that the flicker should be invisible and the hum so high pitched as to be inaudible. But until health tests are carried out, these claims should be treated with caution.

Fluorescent lights also emit higher electromagnetic fields (EMFs) than other light sources, and these may affect some people.

Energy-efficient lighting

More than 20 per cent of the electricity generated in the US is used for lighting, and approximately half this amount of energy is wasted lighting empty rooms or as heat produced by inefficient lamps. As an example, 95 per cent of the energy consumed by the most commonly used incandescent (tungsten- filament) lamp is given off as heat.

Efficiency is a measure of how much visible light is produced (lumens) per unit of electricity. (watts). The more efficient a source the more light per watt it generates. By way of comparison, a 100w incandescent bulb produces 1200 lumens and, therefore, 12 lumens of light per watt, whereas a 20w warm-white fluorescent tube delivers 60 lumens per watt. It is thus five times more efficient and uses only 20 per cent of the electricity

So, from the point of view of energy conservation, it is far more efficient to use fluorescents. In financial terms, fluorescents can make savings of about 80 per cent of the amount spent on lighting.

Compact fluorescent lamps

These are now available as replacements in incandescent fittings. Although the initial purchase price of the lamps ishigh, their long life and efficiency make them by far the cheaper long-term option. Because they do not produce excessive amounts of heat in operation, they also avoid the problem of dust and pollution associated with incandescent lamps. Ordinary fabric or paper shades do much to improve the quality of the light output of fluorescents.

Tungsten-halogen lamps

These are a new generation of incandescents. The miniature quartz glass bulbs give a bright, white light close to daylight in quality. There are two types: first, powerful high- voltage lamps best used for general illumination, such as uplighters; and second, more energy- efficient, low-voltage halogen lights ideal for accent lighting. Both are expensive but lamps can last as long as 4000 hours and can represent savings as high as 60 per cent on lighting energy costs.

Metal-halide lamps

This type of light produces the same powerful white illumination as tungsten- halogen lamps but is as efficient as fluorescents. Again, they are expensive to buy but you should expect up to 6000 hours of use from them.

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