Abstract: A light-emitting device, an electronic device, or a lighting device with low power consumption and high reliability is provided. The light-emitting device includes a first light-emitting element, a second light-emitting element, a third light-emitting element, and a fourth light-emitting element. The first to fourth light-emitting elements include the same EL layer between an anode and a cathode. The EL layer includes a first light-emitting layer and a second light-emitting layer. The first light-emitting layer contains a fluorescent substance. The peak wavelength of an emission spectrum of the fluorescent substance in a toluene solution of the fluorescent substance is 440 nm to 460 nm, preferably 440 nm to 455 nm. The second light-emitting layer contains a phosphorescent substance. The first light-emitting element exhibits blue emission. The second light-emitting element exhibits green emission. The third light-emitting element exhibits red emission.

Abstract: A sensor comprising a solid electrolytic having oxygen ion conductivity to measure the amount of oxygen in molten metal by forming an oxygen concentration cell in which the solid electrolytic element is coated on the surface thereof with mixture which is composed of Al.sub.2 O.sub.3 powders and metallic fluoride powders such as MgF.sub.2 or CaF.sub.2.The present coating does not exfoliate at immersing the sensor into the molten metal and fully maintains wettability of the solid electrolytic element 1 and the molten metal, and since it does not hinder oxygen ion conductivity of the solid electrolytic element 1, the sensor rapidly reaches up to the thermal and electrical equilibrium state, thereby to obtain satisfactory emf wave.

Abstract: There is disclosed an improved electrical contact structure between a solid electrolyte galvanic cell and a powder reference material for detecting the oxygen content of molten metals. The solid electrolyte galvanic cell has a portion embedded in the powder reference material and the portion is irregularly shaped so as to increase the contact area and strength of the joint between the embedded portion and the powder reference material.