By federal law, all trailers (including camper trailers) must have taillights, according to the U.S. Department of Transportation (see reference 1). These taillights have to be sufficiently large as to be visisble, and in correct working order.
The Department of Transportation (DOT) stipulates that all trailers have turn signal lights, again in working order, and sufficiently large to be seen. Most are red or yellow in color.
Brake lights are required. When the towing vehicle's brakes are applied, these lights must turn on, indicating braking.
At least one marker light per side is required. usually red in color.
Individual states may stipulate additional lights, besides the federal regulations. It is best to check with your state's Department of Transportation, to determine what lights are required on your camper trailer.