13 APRIL 05

One of the advantages of timber frame buildings is the speed with which they can be erected, demonstrated to great effect in the barn-raising scene in the film 'Witness' where an entire Amish community pulls together to build a huge barn over the course of a warm summer's day. Given the technical complexities of Tree House, I was not expecting quite such rapid results, but I did hope to enjoy at least a frisson of Harrison Ford's outsider awe.

Unfortunately, just as the erection of our own frame was finally gathering pace, foreman Steve decided to close down the site and go skiing. Skiing! Needless to say, he is under strict instructions to spend the entire week in the bar and avoid all contact with bone-breaking slopes. Happily, the week has not been lost as George has found yet more dirt to shift from one corner of the site to another and off-site there has been a big push to finalise the M&E (mechanical and electrical) drawings, i.e. the location of every pipe, wire, duct, valve, socket and light fitting in the house.

One aspect of Tree House I have long laboured over is the lighting. Of all the magical experiences offered by trees, the vision of sunlight through the canopy on a summer's day is one of the richest. Following this lead, I am keen to create an experience of light in Tree House that is truly out of the ordinary. For daylight, this involves large high-performance windows, contemporary stained glass, bright water and an abundance of foliage. For artificial light, the challenge has been to create an effective and exciting design that does not compromise our energy-efficient goals.

The central energy-saving message about lights has always been 'turn them off'. I won’t argue with this but as we have no Amish aspirations I prefer 'turn them on but make sure they are doing the right job'. Eco-lighting begins with design: thinking through exactly what you want from lighting and choosing the right bulbs, shades and fittings to achieve this. Lighting design is typically divided into ambient, task and accent lighting; poor (or non-existent) lighting design often results in a lot of ambient lighting – bland, bright spaces – at the expense of good task or accent lighting. Ceilings studded with dozens of 40W halogens rarely create interesting or effective living environments.

Whatever your lighting design, make sure the technology is energy efficient. The common incandescent bulb is the apotheosis of hidden domestic eco-horror as only 2% of the fuel energy burnt in the power station ends up as useful light from the bulb, the rest of the energy being thrown away as heat either in the power station or by the bulb itself. Unfortunately, although their inefficiency and short life make them costly, their cheap unit cost keeps them the nation’s favourite.

Although light-emitting diodes (LEDs) are doing well and grabbing the headlines, compact fluorescents (CFLs) are still the most efficient bulbs available. Happily, you no longer have to settle for a bulb that looks like an egg whisk: modern CFLs come in all the shapes and sizes including candle bulbs and miniaturised halogen replacements. One 7W CFL replaces a 30W halogen and will last seven times longer – a no-brainer if ever I saw one. Note, however, that although you can directly replace ordinary light-bulbs with CFLs, you will probably need a new fitting as well when replacing ceiling recessed halogens. See Megaman (www.megamanuk.com) for these and many more possibilities or contact the Energy Saving Trust (www.est.org.uk).

Alternatively, there's the Amish option: oil lamps. Burning the fuel in situ avoids all the energy losses of central electricity generation but the palette for the lighting designer is rather limited. No good for us urbanites: although Harrison Ford looks good in a hair shirt, we composted ours a long time ago.