Sun or floodlight?
This composite picture can be found under
then click "Apollo 11" and scroll manually
down to AS11-40-5863-69.
The picture is a composition of several pictures. 3 of them are shown below. The horizon on the left is slightly modified. The "Sun" should be more on the right according to the rays in the lower part of the image.
The landscape is flat also in the direction of the Sun. The low brightness of the "Sun" and the too high brightness of the non-illuminated back side of the LM (Lunar Module) are indications of a studio picture, specifically if the "Sun" had been shining into the camera.
This composite picture has not been considered in the paper.