Light emitting diodes, known as LEDs are very energy-efficient light bulbs.

Because they’re able to convert 60% of electricity into light, compared to only 5-10% for compact fluorescents, these lights use much less energy.

Compared to halogen bulbs, LEDs use 75% less energy and last 5 to 10 times longer. And though they can cost slightly more in the beginning, the upfront cost of LEDs generally has a payback time of less than 1 year. 

Have a look at this graph from Energy Rating comparing the lifetime cost of LEDs, CFLs and halogens.