I found this site gave helpful info...
http://www.innovitaresearch.org/news/03121401.html
The article posted for this thread suggests that stem cells later reach a stage where they have "committed" themselves to particular type of growth.
Is this what you are disputing? That once the cells became receptive to light they no longer fit the definition?
Correct. Once cells have 'differentiated' they are no longer stem cells. The cells in the title article are no longer stem cells. In fact, the authors mention that they will need a source for these cells from humans and they may possibly use either embryonic or adult stem cells for that source depending on future testing.
Additional information: