 Sometimes some of the calcium was substituted with strontium giving narrower emission peaks.For special purpose or colored tubes the halophosphor was mixed with small quantities of other phosphors, particularly in De-Luxe tubes with higher color rendering index for use in food market or art studio lighting.Prior to the development of halophosphor in 1942, the first generation willemite latticed, manganese-II activated zinc orthosilicate and zinc beryllium orthosilicate phosphors were used in fluorescent tubes.