A LED lamp assembly includes a rectangular electrical box formed of two symmetrical U-shaped frame panels that are detachably fastened together by a tongue-and-groove joint and holding therein a control circuit board that is affixed to two parallel mounting grooves in one U-shaped frame panel by screw nails, a back cover plate and a bracket affixed to the electrical box at two opposite sides for mounting, and an elongated, rectangular light source unit affixed to the bracket and controllable by the control circuit board to emit light.