Abstract: To eliminate the necessity for supervising the composition of a fill being ntroduced to a halogen incandescent lamp bulb, so that the proportion of halogen containing additive and inert gas will be at a predetermined ratio, by spectroscropic and other similar means, the halogen containing additive (8) is placed, in solid or liquid phase, in a mixing vessel at a temperature (T.sub.1) which is in excess of a temperature (T.sub.2) which is necessary to result in the vapor pressure to enrich the inert gas at the predetermined quantity. The inert gas is conducted into the vessel and thereby excessively enriched. The excessively enriched inert gas is passed through a condenser, the temperature of which is accurately controlled to the temperature (T.sub.2) to thereby condense out the excess halogen additive, so that the mixture then will have the desired relationship of halogen containing additive and inert gas; this mixture is then being filled into the lamp.