The 100 W ought to be fine for the low speed. The light might light a little, but the fan should spin.
The idea here is the light bulb is a current dependent resistor. The idea here is if there is a short, the light bulb glows and the current is limited to the wattage of the light lbulb. It's an old trick. It basically prevents you from letting out the "magic smoke" so to speak.
Once you let out the "magic smoke" the device ceases to function, therefore magic smoke is the reason why electronics actually work. <G>.
