Abstract: The invention provides an improved method of construction of a prefocus lamp, to improve positioning of the filament relative to the lamp cap, and a lamp so made. The lamp envelope has a pinch seal with V-shaped grooves into which a resilient ring is sprung. This assembly is a sliding fit in the lamp cap and is slid therein to have substantially only line contact between the ring and the cap. The envelope can then be relatively easily rocked and otherwise moved in the lamp cap to be precisely positioned. When the positioning is complete solder previously placed in the cap is melted, the position being such that it flows over the ring and fixes the ring to the lamp cap.