Comment by Asooka

AO is only half of what's needed, you need full GI for realistic corners. One phenomenon that the article didn't point out, but you can simulate trivially easy in Blender, is that corners that are perfectly lit are actually lighter, due to more reflected light reaching them. To observe, just set two grey planes at 90 degrees to each other and add a point light at medium distance. Render with Cycles. Pay attention to corners in well lit places with plain smooth diffuse walls like conference rooms and you will be able to spot it in real life too!