Any person or firm engaged in excavating or otherwise in any manner obstructing a portion of or all of any street, sidewalk, alley, or other public right of way, at all times, from one-half hour before sunset until one-half hour after sunrise, shall cause proper warning lights to be secured, operating, and conspicuously posted around the excavation. The warning lights shall conform to the requirements of the Ohio Manual of Uniform Traffic Control Devices and to any requirements imposed by the Director of Public Service.