As an alternative it shall be deemed a compliance with §§ 56-5-5060 and 56-5-5070 in the event the person operating any motor vehicle described therein shall carry in such vehicle three portable reflector units on standards of a type approved by the Department of Public Safety. No portable reflector unit shall be approved unless it is so designed and constructed as to include two reflectors, one above the other, each of which shall be capable of reflecting red light clearly visible from all distances within five hundred to fifty feet under normal atmospheric conditions at nighttime when directly in front of lawful upper beams of head lamps.