I am fitting an external light and want to reduce the amount of cabling and cable cover to a minimum.

For fixed wiring, the lowest is 14 AWG. For a light fixture on a wall, you can use 16 AWG but the wire to the box must be at least 14. What exactly are you planning to do.

As Brian said, the minimum size cable for residential is 14 AWG. Fourteen gauge wire is rated for 15 amps and must be protected by a maximum 15 amp breaker.
Just for you information 60 watts at 120 volts is 1/2 amp.