There really isn't a unique answer to the question about how high a wattage you can use in a fixture that is labeled as a 40 watt max fixture. If the fixture was made to be used with CFL bulbs, it may be labeled based on the "equivalent to" wattages of CFL bulbs. Or, if it is made to be used with any type of bulb, it would probably be rated based on the maximum current and the maximum heat load from the bulb, so the 40 watts would mean 40 real watts, not "equivalent to" watts. When I used CFL bulbs I always used sockets and wiring that were rated for real watts, and it is still possible that all fixtures are rated for real watts. A good way to decide would be, for a commercially available light fixture, to see what specific bulbs are recommended to be used - CFL bulbs or some other kind of bulb. If it is CFL bulbs I would assume "watts" means "equivalent watts", but if it is other bulbs, such as incandescent bulbs, I would assume "watts" mean real watts.