Does a 600 watt garden lights transformer pull 600 watts all the time or just the load from the lights you have on it?

Watts are power. If the lights were mostly or totally switched off, you'd have a circuit generating 600W of heat somewhere if the transformer still took 600W, not only that, but when you switched on, the 600W that the transformer was consuming, would not disappear, so the total drain would be 1.2kW. ---- Don't understand the above answer. The 600 watts on the transformer nameplate is the maximum amount of wattage that the transformer can produce and still be within its safety limits. It doesn't draw that wattage all the time. If you had two 50 watt lamps connected to the transformer then the transformer has the capacity of 500 watts left. The transformer will only produce the wattage that the load requests. The transformer has the ability to supply twelve 50 watt bulbs. 12 x 50 = 600. Any more bulbs than 12 and the transformer is in an overload condition.