Only 240 watts max?

You would confuse a typical home owner with this spec. Apparently the resistive characterics of the tungsten load is different in some way to that of the appliance that can handle almost 5 times the stated wattage. It would be out of spec to run from this device with two 150 watt bulbs that are incandescent since most bulbs use a tungsten fillament. Usually the case stated is the other way around. Inductive motors in appliances have a higher startup wattage requirement than resistive lights. Another way to look at this situation is the overall rating on the appliance is 1200 watts of which and the lighting maximum for tungsten lights is 240 watts.