Colours of wires used in electrical installations.
Current (amperage) ratings for the plugs and sockets.
Size of wire used in the fuse.
Fuse rating for the plug or Fused Connection Unit.
What is the power of your appliance in watts? - W
Maximum summary power and quantity of lights which might be
used with the certain switch. You can use this calculator for lighting circuit calculation instead, which is a bit difficult, as different lights could be used within the same circuit.
What is the power of single light bulb, which you intend to use in a set in the room?