Light emitting diodes (LEDs) have largely replaced CFLs, which are more efficient still, turn on instantly at full brightness, and are available to fit pretty much any light fitting in the home. LEDs produce light from the electricity flowing through them. Within a bulb, you will find a large number of LEDs to create sufficient brightness.
If you replace all the bulbs in your home with LED lights, you could save £65 a year on your electricity bills.