black electrical tape won't fully cover it
Actually, it would, but you have to be prepared to spend half a roll of it. I used 3M 780 Vinyl Electrical Tape for the purpose.
The trick is, you need to cover the
whole of the outer circle with the tape, leaving only a hole for the light censor at the bottom and the lens itself. the tape must come tight to the edge of the protruding lens, but must not obscure the view. If you don't want to cut semi-circles in the tape, use the iris approach, overlapping several short pieces of tape along the edge.
The upper part of the outer circle needs to be covered with a double layer of tape to prevent any heat/IR light seeping through.
But... it's really unfortunate that we are forced to do that still, when all D-Link could do is to enable a switch in the firmware!