Fluorescent bulbs have an advantage in that they are more energy-efficient than conventional bulbs. This type (E27) is one of the most common and fits most light fixtures.
From OnBuy
Crompton Lamps 15W Golfball B22 Dimmable Colourglazed IP65 Blue
Lamps 2U Direct
Crompton 25BBC-GLZ BELL 01512 15 watt BC-B22 Blue Golfball Light Bulb