Any person engaged in or employing others in the excavation of any street or in any manner obstructing a portion or all of any street, shall, at all times during the night, install and maintain at least two illuminated red or amber lamps which shall be securely and conspicuously posted on, at or near each end of such excavation or obstruction. If the space involved exceeds fifty feet in extent, then at least one additional lamp for each added fifty feet or portion thereof excavated or obstructed shall be installed and maintained.