The National Trust is today launching a ‘Big Switch’ project to change 40,000 light bulbs across its historic houses, offices, shops, restaurants and holiday cottages to low energy alternatives.

Once installed, the new bulbs will save 2,223 tonnes of carbon per year and will reduce energy and maintenance costs by £431,000 each year. The Trust will plough these savings back into reducing the environmental impact of its properties even further.

Changing light bulbs may sound simple, but there was a particular challenge for the Trust. The first generation of energy efficient light bulbs, called compact fluorescents, produced higher levels of ultraviolet light than incandescents. And while all light is damaging, UV is the most harmful for sensitive materials such as the delicate watercolour paintings, textiles and wallpaper found in many National Trust houses.

There was also the issue of how these bulbs look in a historic setting, an issue shared by many homeowners living in older houses throughout the UK.

‘Lighting is really significant for the National Trust, perhaps more than many people appreciate,’ says Katy Lithgow from the Trust.

‘Good lighting can help to bring collections alive and can help visitors to enjoy historic interiors. Too much exposure to light, however, is detrimental. Ultraviolet is the most damaging part of light, but happily ultraviolet is not necessary for us to be able to see. If this element is reduced or even eliminated from light sources, the benefits are significant.

‘If the Trust can solve the problem of finding low energy lighting solutions in its houses, then the same is probably true for householders across the country.’