How does cfl lamps in conservation of energy?

CFL means compact fluorescent lamp

It can save five times its purchase price in electricity cost because it contains toxic mercury that is equivalent in working: electrons that are bound to mercury atoms are excited to states where they will radiate ultraviolet light as they return to lower energy level, this ultraviolet light will be converted into visible light as it strikes to the coating of the bulb. Like LED that is high-efficiency house lighting.