Design space: Energy-efficient lightbulb - FT.com Product: Cree LED lightbulb Design: In-house Territory: North America Sales of energy-efficient lightbulbs in North America are flat, with less than 20 per cent of a potential 5.6bn domestic light sockets being fitted with them. US-based Cree, manufacturer of energy-efficient lighting products, believes that many consumers are put off by the "twisty," unconventional look of some energy-efficient bulbs. So the company set out to introduce versions that looked more like a traditional incandescent bulb. "Twisty" bulbs emit light from the whole bulb, whereas the light from conventional bulbs comes from their centre. To achieve this effect, Cree designed a filament tower within the bulb, with the LEDs - light-emitting diodes - held in place at the centre of the bulb on an aluminium pillar. ©Hand Out Cree LED lightbulb This arrangement allows the bulb's internal workings to be housed in a conventional bulb shape. In addition, Cree's product is made of glass, rather than plastic, which is common among energy-efficient bulbs. Glass transmits light better and is less susceptible to degradation from the light itself. The Cree LED bulbs went on sale in March online and through The Home Depot stores, at $9.97 for a 40-watt bulb and $12.97 for a 60W bulb.