I'm not sure which LED bulbs you have, but when on, they all dissipate 5 or 6 watts of power, which I can certainly feel. But the OP was asking about parasitic draw when the bulb was off. If its more than a watt or two confined to the very small area in the bulb base, you should be able to feel a slight amount of heat. I have the Zigbee GE bulbs and they are very cool, indicating less than 1 watt. I know in the "olden days" UPB switches definitely drew 4 or 5 watts and were definitely slightly warm to the touch.