Halogen and LED capsules are ideal for the smallest of light fittings, and are commonly used in cooker hoods, under cabinet lighting and integrated light fittings. They are very compact but offer a bright light for their size. There are two types of capsule bulbs: G9 and G4. The biggest difference between the two capsules are their voltages. G9s operate off the mains voltage (220-240V), while G4 capsules are low voltage (usually between 12V and 24V) and need to be installed with a compatible transformer to transform mains voltage into a lower one suitable for the bulb.