With Spring here, and the summer right around the corner, you’ll probably be doing a lot more entertaining and relaxing outside on your porch, deck, patio, etc. You’ll need adequate lighting to entertain throughout the night, but you can’t just use any old light bulb in your outdoor light fixtures.
Start off by checking the Ingress Protection rating of your fixture, this will tell you how protected it is against water and moisture. A rating of IP-65 or lower means it is weatherproof, but a rating of IP-66 or higher means it is practically waterproof. When in doubt, go for a higher rated fixture, you can never have too much protection.
Check the packaging for an outdoor rating. Standard flood lights and incandescent light bulbs can be used outside, as long as they are not directly in contact with rain or other elements. They are best used in covered locations. This goes for Christmas lights as well, not all of them are meant to be used outside. Read the label before decorating your home for the holidays.
Unless you are using halogen PAR lamps, standard halogen bulbs cannot be used outside unless they are protected by an outdoor rated fixture.
Typically, CFLs are meant for indoor use only. They can stand heat, but will not make it in cold weather or rain. The exceptions to this are bug lights and Cold Cathode CFLs (CCFL). Bug lights keep insects away without killing them. CCFLs are used to make neon signs, which can stand below freezing temperatures.
You won’t see fluorescent bulbs being used outside, but more so in home garages and parking garages. The temperature range of a standard T8 bulb will tell you if it can handle the heat or cold. Summer heat usually is not a problem, but any temperature below zero, will leave you in the dark.
For LED use outside, they will need to have an outdoor rating. If you are using a sealed fixture, it is possible to use an LED bulb rated for enclosed fixtures. If you need an LED that will come into direct contact with the elements, use one with a UL rating for wet locations. LEDs that will be used on something like a porch with an overhead covering, will need at least a damp location UL rating.