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Lighting manufacturer Philips, which showed the luminaires on the right at the recent Frankfurt Light and Building Fair, is refining its products to take account of the latest research into the effects of daylighting on human behaviour. As more becomes known about this subject, it should have an impact not only on lighting design, but also on the design of buildings in general How are your special ganglion cells doing?

The answer should be pretty nicely with the advent of spring, but the chances are that, unless you were in full-time education very recently, you have never heard of them since they were only discovered in 2002. Philips, however, is one lighting company that is taking them seriously, as they are the cells in the eye that respond to daylight.

Numerous studies have shown the importance of natural daylight to health and well-being. For instance, studies in the United States (the source of most information on the subject) by researchers at the National Renewable Energy Laboratory, show that students in school classrooms that have daylight perform significantly better than those who are in artificially lit environments.

In the UK the National Association of Rooflight Manufacturers is eager to promote the use of roofl ights in relatively deep-plan buildings. It is concerned that restricting glazing to windows may satisfy regulations about the percentage of glazing but will actually leave dark spots, leading to a need for artifi cial lighting. This is an important environmental issue. With Part L and its more stringent requirements about U values, turning over part of the roof to glazing may appear unattractive, although as with all glazing systems, the thermal performance of glazing systems is now very respectable. In fact, concern is more likely to be with overheating than with heat escape, and even this can be dealt with by shading, blinds and intelligent design. Much more important is the signifi cant energy saving that comes from being able to eschew the use of artificial lights - and the health benefits as well.

We probably all accept that natural light is desirable but it is not always achievable in the most straightforward form. This is where companies like Monodraught with its Sunpipes come in. These tubes reflect natural light down into spaces that otherwise have no access to it, and the company insists that the effect is almost as good as having a window. Sunpipes are used in applications ranging from doctors' surgeries to prisons and, since the strength of the light varies with the cloudiness and time of the day, the company maintains that occupants still have a sense of engagement with the outside world.

But for some, of course, natural daylight is not an option. That includes shiftworkers, people in call centres and all of us who work more than six hours a day in winter. Studies show that being awake at night or spending long periods without daylight disrupts the balance of the sleep and stress hormones, melatonin and cortisol. Not uncontroversially, designers have used high levels of artificial lighting in an attempt to fool people's body clocks. But this is where those special ganglions come in. It turns out that these are the cells that control our hormone levels and our body clocks, via the pineal gland. And they respond not to the visible spectrum but to a much bluer range of light. Get that right and you can signifi cantly lower the overall level of light and still enjoy the beneficial effects. That is why companies like Philips are getting excited and other organisations, such as Arup Facades, are studying the wavelengths of light that actually make it through our glazed enclosures.

Daylighting is a relatively new field of study but it appears there may be light at the end of the tunnel.

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