Spray-coating method of window forming in tubular lamp

A method of applying a coat of a suspension or solution to the inner wall of a tubular lamp, which coat is provided with a longitudinal slot, which comprises:

• spraying the suspension or solution with a plurality of jets onto the inner wall of the tubular envelope of the lamp, after positioning said jets in a common plane which (1) intersects a portion of the envelope immediately adjacent to the slot to be formed (2) is parallel to the longitudinal axis of the lamp and (3) is disposed at an included angle of less than 75.degree. intermediate said common plane and another plane which is tangentially disposed to said envelope at the line of intersection of said envelope and said common plane, said jets being also disposed at an angle greater than 45.degree. with respect to the line defined by the intersection of said common plane and said envelope.