How bright are low-energy lightbulbs?

While it's hard to object to low-energy lightbulbs—they use a fifth of the electricity consumed by traditional bulbs—it hasn't been easy to like them. The first compact fluorescent lamps (CFLs), launched in the 1990s, flickered to life slowly, cast a dim, cold, grey light and often poked out of lampshades—a poor aesthetic substitute for the warm yellow glow of the incandescent lightbulb Thomas Edison developed in 1879.

As bans on incandescent bulbs have spread around the world, low-energy lightbulbs have become the new normal. CFLs shed most of their early problems, but are set to be superseded by light-emitting diode (LED) bulbs, which are more expensive but can last up to 30 years. Halogen bulbs most closely replicate the effect of incandescents but use 30% less electricity—which sounds good until you know the savings achieved by CFL (around 80%) and LED (around 85%).

There are now so many low-energy lightbulbs that it's all too easy to grab the wrong one. If it's an LED you could be stuck with your mistake for years, so it pays to read the label—and to understand it, because the vital statistics have changed. First, forget about watts, or rather, stop equating them with brightness. Wattage determines energy consumption; brightness is measured in lumens (lm). So the equivalent to a 60W incandescent bulb emitting around 700lm could be a 13W CFL, 12W LED or 53W halogen. Broadly, a really bright bulb will be 1,300lm and a dim one 400lm.

Then consider the bulb's colour temperature, which is measured in kelvin (K): 2,700K is "warm white", as close as a CFL can get to a cosy Edison glow; above 3,000K is "cool white", which tends to look blue or grey. "Warm white" sells best in Britain, "cool white" is favoured in Europe. Finally, check the Colour Rendering Index: halogen has a CRI of 100%, matching daylight; CFLs and LEDs tend to score 85-90%. Less than 80% and colours look strange.

The label should also state whether the lightbulb will come on instantly—some CFLs still take time to warm up—and whether it's dimmable. Basic CFLs aren’t, because their wattage is too low. Dimmable LEDs might not work with your existing dimmer switch. Play safe with halogen: Philips EcoClassic range (from around £3, philips.co.uk) is fully dimmable and should last twice as long as an incandescent.

Halogen is also—to my eyes—the best light to read by so it's a good choice for table lamps. Save LEDs for your pendants, because the bulbs are heavier—heavy enough to make an Anglepoise droop—and can be so futuristic-looking that however much energy they’re saving you’ll want them out of your eye-line. In fact all bulbs vary so much that if you want one for a particular lamp it’s worth taking it to the shop. But go to one that sells all three types of low-energy bulb—remarkably, not all do. One lighting supplier I visited had no CFLs, dismissing them as "yesterday's technology". Across London, Geoffrey Harris, who has sold contemporary lighting since the 1960s, doesn't sell LED because "it's too expensive and the stock changes too fast", and because CFLs do a decent-enough job at a fraction of the price. They are fine for general ambient light and no longer have to be ugly or enormous. If you don't want to look at a fluorescent stick or a spiral, find one encased in a globe, such as the Megaman Compact Classic range (around £6; megamanuk.com).

Low-energy and long-lived, LED is undoubtedly the future of domestic lighting—particularly now that Osram has introduced its better-priced led Star Classic A range (around £10; osram.co.uk). But there's no urgent need to change every light in the house just yet—proceed bulb by bulb instead. By the time the last filament breaks, more LEDs may have come down to CFL prices. Eventually, we won't be changing lightbulbs at all: new lights will be sold with integral LED chips that will never need replacing. The future looks a little brighter.

Illustration Richard Rockwood