The quest of a perfect wash of light on a wall I always thought of as a bit “four sprung dur , technic” if you get my metaphor…the light had to be even as it fell on the surface and with a uniformity from top to bottom of no greater than 3:1 as the human eye would not detect the flow from say 300 lux at the brightest to only 100 at the lowest area. The pursuit of engineering excellence would then (theory goes) would provide the perfect partner of light to Architecture, assuming this is how each and every architect would want their “wall” to be seen?
In the same breath the luminaire should be as invisible and integrate to the fabric of the build, thus “flush” mounted be that in the ceiling or the floor, this then always left a small edge of a wall’s surface out with the distribution of the light (again top or bottom), secondary reflectors, clever optics, tiny edge lips to the luminaire, feathering the edge of the glass, reflector…all in the pursuit of the same goal.
I too was for a time obsessed with the “holy grail” and taught many classes of budding lighting designers the same “true” way to light a wall…but now in my third decade of lighting and many, many conversations and equally hundreds of projects with Architects and Landscape architects I have come to a different conclusion…”non uniformity” daylight moves across a top lit gallery, the art inside was always planned to be seen from different directions and external daylight moving, so too the different experiences and views of humans allow for different interpretations, different moods and feelings every time you see the space. No longer are we designing a static single perfect light and that little problem of the shadow edge seems so inconsequential, we put people first and say
“who will see this, where from, under what variables of time and daylight …and what do you want them to feel”?
I expect the answer to this question to be multiple and varied as will be the light scenes we create to achieve those goals.