Lighting is one of those things that interior decorators need to get perfectly right. No other element can transform a room quite so drastically. So it helps to know as much as possible about the technical side of it. You don’t have to be an electrician, but if you know what you’re doing, you’ll get stunning results fast.

Donald Trump recently stood up for old, incandescent light bulbs. “The light’s no good” he said, of new energy-efficient CFL bulbs, “I always look orange. And so do you!” It’s not true, of course, but it boosted the incandescent bulb industry in the USA.

In Europe, of course, we all look orange because incandescent bulbs have been phased out and there are three main types of light bulb available: CFL’s or compact fluorescent lamps – those chunky energy-saving bulbs that replaced incandescent bulbs; halogen lights and LEDs.

Of these three, LEDs are the most energy efficient, saving up to 90% of the energy of an incandescent bulb. CFL’s save from 60-80%, while halogen bulbs save just 20-30%.

LEDs are undoubtedly the real game- changers and are almost certain to be the lighting of the future. They’re incredibly versatile, offering bulbs that change colour and brightness, and can be installed indoors and outdoors in almost any area you can think of.

They can be expensive, sure, but they last for years and save loads of energy. And they’re getting cheaper – IKEA’s standard Ryet bulb lasts for 15,000 hours, uses 85% less energy than an incandescent and costs €1.25.

The bad news for old stick-in-the-muds is that we’re going to have to forget about wattage and learn lumens. This is easy, though, and all you have to do is apply the formula P (W) = Фv (lm) / η (lm/W). OK, then, maybe not so easy. Let’s just start with the fact that a 450 lumen bulb is equivalent to a 40 watt bulb; a 1,000 lumen standard bulb such as the Ryet is around 75 watts and a 2,600 lumen bulb will give 150 watts.