A detecting device comprises a detecting sensor (52) for detecting UV radiation and a protecting screen (53) transparent to UV radiation and arranged for protecting a lens (54) of said detecting sensor (52), said detecting device further comprises an extension arrangement (55) provided with an elongated element (56) interposed between said detecting sensor (52) and said protecting screen (53) and defining a through channel (57), said channel (57) having a first end (58) covered by said protecting screen and a second end (59) facing said lens (54).
