A bulb adaptor is provided which includes a mounting housing, a rotating mechanism, a first connecting member and a second connecting member. The mounting is provided with threads. The first connecting member includes a convex first live contact part and two first metal connecting parts. The second connecting member includes a convex second live contact part, a neutral contact part and two second metal connecting parts. The second connecting member is arranged crosswise with the first connecting member. The rotating mechanism includes a rotating member and a convex part. The convex part has a first position and a second position. The first position is where the convex part is in electrical contact with the two first metal connecting parts, and the second position is where the convex part is in electrical contact with the two second metal connecting parts. The rotating member is slidably connected with the mounting housing.