Another photograph of the photocell equipment on what I'm pretty sure was 111. It is the clarity of this photograph that has allowed me to conclude how it operated. The rotary control on the panel at the left has a label saying "Time delay". This allows adjustment of the time between the cell beam ceasing to be interrupted and the doors closing, to give passengers time to get clear of the doors.
The objective would be to increase safety at these doors, which weren't directly supervised by the driver. As can be seen from the Panther Cub interior views, the much simpler expedient of a mirror was eventually adopted, although I'm not sure that was ever retro-fitted to the Tiger Cubs.
