Doc Savage developed the Light-spot cartridge for use as a type of illumination round. It is described in Fear Cay as being a mixture of thermite and magnesium, and would generate a brilliant white light wherever they struck. Some of the ammo drums used with Doc Savage's Machine Pistols are loaded with an alternating pattern of five light-spot rounds and five Mercy Bullets. They are very similer in design to the Ultraviolet Bullets, though they differ in the fact the light spot cartirdges produce a visible light while the ultraviolets dont.