Safety is vital when operating electrical items in close proximity to water. All aquariums need electrical power to operate their lighting and filtration systems and most use mains electricity at 240 or 120 volts. This can cause serious electric shock should the Fishkeeper drop or drench the electrical items in the aquarium water. The Reef One range of aquariums is designed to be extremely safe and therefore all its electrical items operate at the safe low level of 12 volts ac. To protect the Fishkeeper and children from electric shock Reef One aquariums use a plug top AC transformer that plugs into your electrical mains socket and ‘steps down' the mains voltage to a much safer 12 volts ac. The 12 volts is made available in the bottom of the AC transformer through two din sockets (see image). Either socket can be used for the halogen light wire plug or the air pump wire plug as both sockets are interchangeable. The LED light if used in place of the halogen light can be plugged into either socket. Special Note : The AC transformer is capable of handling a maximum of 20 watts power and incorporates a non replaceable safety fuse that will blow, permanently damaging the AC transformer, if a halogen bulb of greater than 20 watts is used to replace the 10 watt bulb supplied with the light.