Gotcha. Those are reasonable questions. I don't know enough about the TSBD building work schedules (or even how the lighting on the various floors was controlled) to know if this would be an issue or not. That doesn't have a whole lot to do with the issue of whether Baker and Truly would have had a problem seeing where they were going in the stairway during the day if the power had been out during that time.
The warehouse staff worked till at least 4:45 and in winter on a dark overcast day I wouldn't want to be relying on any outside lighting.
Mr. BELIN. What were his hours of work to be?
Mr. TRULY. His hours were from 8 in the morning until 4:45 in the afternoon. His lunch period was from 12 to 12:45. As for the light switch I don't know what this controlled but it appears to be a light switch and its location is close to where you enter this floor.
As for the stairwells being fully enclosed, I don't think they are.
In this clip from Ruby & Oswald which was filmed in the actual TSBD it suddenly dawned on me that there is no door leading up to the 2nd floor, and blah blah blah I know it's a decade later and according to you probably irrelevant, but nonetheless let's see where this goes.
The 6th floor stairwell leading down appears to have no door.
From these angles photographed not long after we see the 2nd floor stairwell going down also appears to have no door and what is also visible is a different type of light fixture that presumably lights up the sign and the stairs leading down to the first landing.
JohnM