Ceiling Fan light enclosure - CFL only lights
Typically the reason for the low wattage rating is because of small gauge wire used in the fixture that would not be rated for much higher wattage/current draw required by 40 or 60 watt incandescent bulbs. Incandescent or halogen bulbs burn much hotter and in an enclosed space can fail prematurely. As far as using LED bulbs, they should work fine. The draw is very low and the heat is not much more than CFLs. I have been using LED bulbs in enclosed fixtures for a few years now with no problems.