A sidestep. The illumination set found in the box is of an unusual type. We know these sets are post war modifications made by the Norwegian army.
The connector that holds the lamp is much smaller than standard sets. The knob on the right controls the intensity of the light.
The lamp piece fitts the modified connector on the periscope.
There is a tiny light bulb inside. It still works.
This SR-9 has a Norwegian history, that’s also not unsual.