The present invention relates to a method for manufacturing a linear LED light source, comprising: providing a tubular glass envelope that is open at its proximal end and its distal end; inserting a light source mount assembly comprising one or more LED units into the tubular glass envelope; forming a distal hermetic seal at the distal end such that a distal opening remains at the distal end; forming a proximal hermetic seal at the proximal end such that a proximal opening remains at the proximal end; filling the tubular glass envelope with a gas filling; and sealing the distal and proximal openings to obtain a sealed lamp envelope; wherein a flow of coolant gas through the tubular glass envelope is maintained during the formation of the proximal hermetic seal and/or distal hermetic seal if the light source mount assembly is inserted before the formation of the respective hermetic seal.