To solve a problem of deteriorating an outward appearance by causing an irregular color at color bulb lighting time in a conventional color bulb wherein a part of the light of a wave length area to be reflected passes through an interference film formed on a glass bulb surface by a characteristic difference in incident angles of the light from a filament.

The interference film 6 formed on the surface of a glass bulb 2 of the color bulb 1 is formed so that the optical film thickness of a part becoming 30° or more in the incident angle of the light to the surface of the glass bulb 2 from a central position C of a filament 3 is set to 1.05 to 1.1 times the optical film thickness of a part smaller than 30° in the incident angle, and the irregular color is eliminated at color bulb 1 lighting time.