Electric lamp and method of depositing a layer on the lamp

摘要

An electric lamp has a light-transmitting lamp vessel ( 1 ) with a curved vessel portion ( 11 ) accommodating an elongated light source ( 2 ). Part of the curved vessel portion is provided with an optical interference film ( 5 ) of which the thickness differs locally. The interference film is thicker at locations on the curved vessel portion substantially parallel to the source axis as compared to other locations on the curved vessel portion. A method of depositing a layer of a material on a such an electric lamp, includes the steps of: moving the lamp vessel past sources of deposition material while simultaneously rotating the lamp vessel along its vessel axis, locally shielding the lamp vessel to locally reduce the thickness of the deposited material on the lamp vessel, the shielding means being provided in the vicinity of the lamp vessel and rotating at substantially the same speed as the lamp vessel.