That is an excellent question, and one that I have come across many times.

The short answer is....You should NEVER use any bulb or heat emitter that is rated higher than the fixture is rated. Wattage does not refer to brightness. It refers the the amount of energy being used. If a fixture is rated at 75 watts, then it means the wires and everything else are able to handle up to 75 watts.

Placing a CHE or incandescent bulb that is rated at 150 watts will still draw 150 watts worth of energy (even if it doesn't put out light) causing an overload on the smaller fixture. Which, in turn may cause some pretty negative side effects!

Even though you may be able to get away with it for a little while, your best bet would be to get the appropriate wattage CHE that the lamp is rated for!

best of luck and I hope this helps!