Abstract
Escape factors for upper and lower limits to the source function appropriate for spherical geometry have been evaluated using a set of Stark-broadened line profiles, computed with different approximations, for the Lyman- alpha line of argon XVIII. The method used to compute the escape factors, which is based on a general formalism can be applied to any kind of line profile and is suitable for any geometry. Comparisons are made with previous calculations that used Holtsmarkian line profiles and significant differences are noted.