Any person engaged in or employing other in excavating or otherwise in any manner obstructing a portion or all of any street, sidewalk, alley, or other public way, at all times during the night season shall install and maintain at least two illuminated red lamps which shall be securely and conspicuously posted on, at, or near each end of the obstruction or excavation, and if the space involved exceeds 50 feet in extent, at least one additional lamp for each added 50 feet or portion thereof excavated or obstructed.