Seven thermally and optically efficient LED units and two control units are disclosed. Flashlights utilizing these LED units and control units are also disclosed. Such a flashlight mainly includes a cylindrical housing, a cylindrical rear cap, one of the seven LED units, one of the two control units. Each LED units are interchangeable between different emitting colors. Each LED unit mainly comprises a metal base, a reflector if the metal base is not a reflector itself, a leadframe formed attaching one or more metal pins to a printed circuit board, one or more LED dies mounted on the metal base, optical material disposed over the LED dies, and an optional lens to further focus the light.