 "Flame arc lamps" were introduced where the carbon rods had metal salts (usually magnesium, strontium, barium, or calcium fluorides) added to increase light output and produce different colours.In the U.S., patent protection of arc-lighting systems and improved dynamos proved difficult and as a result the arc-lighting industry became highly competitive.Brush's principal competition was from the team of Elihu Thomson and Edwin J. Houston.