A lamp (L) having tubular end contacts (L1) adapted for insertion into opposite lamp holders (P), each lamp holder (P) having a body (S) in an insulating material and a contact element (C) shaped to provide a seat for the lamp contact (L1). In one embodiment, the seat comprises a cylindrical central portion (C1) positioned between flexible opposite arched walls (C2) with two upper divergent flanges (C2a). The lamp end contacts (L1) are positioned between the flexible arched walls (C2) of the contacts (C), in order to receive the cylindrical parts (C1) of the seats of the contact elements (C) inside the end contacts (L1) of the lamp (L). By the rotation of the lamp (L) around the cylindrical parts (C1) of the contact elements (C), an unwanted removal of the lamp (L) from the lamp holders (P) is prevented.