One other point that the picture on your screen does not necessarily illustrate is that an exhibition at 50 lux is rather depressing. There is nothing that does more to give conservators the reputation of kill-joys than the sight of one, with frown and luxmeter, patrolling a new exhibition the day before the opening, telling the technician that he must turn down the lights. Conservators need to understand light, because no one else is interested in the physics and psychology of exhibiting in a dim light. Architects are always trying to increase the brightness of indoor places, making vast atria with enough light to ensure exuberant growth of a miserably limited selection of exotic plants. It was not always so, as many dimly magnificent churches confirm.
Light is a difficult subject.
The elegant abstractions of physics are complicated by the brain's insistence on interpreting the signal that reaches it from the eye. One cannot get far without understanding the basic units.