The watt limits in light fixtures and lamps are important because the light bulbs generate heat. So, if you're talking about traditional incandescent bulbs, you need to follow the limits that are posted on the light fixture.

However, you can swap in a 60 watt CFL bulb into the light fixture in place of the 40 watt incandescent bulb. That's because the 60 watt CFL is equivalent of a 13 watt incandescent bulb. It generates far less heat -- you can feel it by holding your hand up to it -- and it consumes less energy as well.

Keep in mind, if your light fixture has a dimmer switch, you can get CFL bulbs that are dimmable as well. But make sure you specifically look for a 60 watt CFL that says it is OK for a dimmer switch because they don't all work in that situation.