An electroluminescent device comprises a cathode and an anode; and located therebetween, a fluorescent light-emitting layer (LEL) comprising at least one fluorescent emitter and a host, together with at least one phosphorescent light-emitting layer comprising at least one phosphorescent emitter and a host, and having a spacer layer interposed between the fluorescent and phosphorescent light-emitting layers. The materials within these layers are selected so that the triplet energy levels of certain components satisfy certain interrelationships. The invention provides devices that emit light with high luminous efficiency at low voltage.