I'm not a fan of the covers but here's what the state has to say about it according to Tennessee Code 55-9-402.
(b) (1) Every motor vehicle shall be equipped with two (2) red tail lamps and two (2) red stoplights on the rear of the vehicle, and one (1) tail lamp and one (1) stoplight shall be on each side, except that passenger cars manufactured or assembled prior to January 1, 1939, trucks manufactured or assembled prior to January 1, 1968, and motorcycles and motor-driven cycles shall have at least one (1) red tail lamp and one (1) red stoplight. No non-emergency vehicle shall operate or install emergency flashing light systems such as strobe, wig-wag, or other flashing lights in tail light lamp, stoplight area, or factory installed emergency flasher and backup light area; provided, however, that the foregoing prohibition shall not apply to the utilization of a continuously flashing light system. For the purposes of this part, “continuously flashing light system” means a brake light system in which the brake lamp pulses rapidly for no more than five (5) seconds when the brake is applied, and then converts to a continuous light as a normal brake lamp until the time that the brake is released.
(2) The stoplight shall be so arranged as to be actuated by the application of the service or foot brake and shall be capable of being seen and distinguished from a distance of one hundred feet (100¢) to the rear of a motor vehicle in normal daylight, but shall not project a glaring or dazzling light.