  The Phong illumination model is still widely used in realtime 3D
visualization systems. The aim of this article is to document problems with the
Phong illumination model that are encountered by an important professional user
group, namely digital designers. This leads to a visual evaluation of Phong
illumination, which at least in this condensed form seems still to be missing
in the literature. It is hoped that by explicating these flaws, awareness about
the limitations and interdependencies of the model will increase, both among
fellow users, and among researchers and developers.
