Exterior light fixtures look more rugged than interior ones for two reasons: they are generally made of noncorrosive material and are able to withstand the elements. The second is that they are well sealed to keep water from coming in contact with the electric parts inside. The only other significant difference between the two types of fixtures is that they are sometimes designed to mount to different types of surfaces. Otherwise, they use identical bulbs, draw the same amount of power and connect to power the same way.
While it’s generally safe to operate an exterior light fixture indoors, the reverse isn’t necessarily true — you can’t use most interior fixtures outdoors. They aren’t sealed against moisture and will probably stop working during the first heavy rain. Moreover, they aren’t corrosion resistant and could become electrocution hazards if the parts that cover the electrical connections deteriorate. You may be able to use certain interior fixtures, which are UL-rated as “damp,” in covered porches or other covered outdoor areas. If you aren’t sure about a fixture’s rating, it’s better to find a suitable place for it indoors.