Abstract: A lamp includes a glass bulb sealing a filament therein. A light interference film is formed on a surface of the bulb. The film has at least five layers and is formed by alternately stacking a low-refractive index layer comprising silicon oxide and a high-refractive index layer having a refractive index higher than said low-refractive index layer. The low-refractive index layer contains, at least one additive selected from the group consisting of phosphorus and boron.

Abstract: There is proposed a bulb which is coated with an optical interference film consisting of alternately formed thin titanium oxide layers and metal oxide layers of a lower refractive index than that of titanium oxide layers. The characteristics of the bulb reside in the formation of each titanium oxide layer which is formed by thermal decomposition of a mixture consisting of 5 to 50 parts by weight of Ti(OR).sub.4 and 95 to 50 parts by weight of polymerized Ti(OR).sub.4, where R are C.sub.1 to C.sub.18 alkyl group, --OCOR' (R' is C.sub.1 to C.sub.18 alkyl group or --X radical which is capable of forming a chelate ring with titanium.