Did Renaissance painters use projectors?

Several years ago, artist David Hockney published a controversial book claiming that some famed Renaissance painters may have used optical projection systems to achieve the amazing realism achieved on their canvases. Stanford university physicist and art historian David Stork calls bullshit on Hockney's theory. Stork used computer imaging software to determine the source and intensity of the light depicted in the painting. In a scientific paper, Stork claims that the only light source was a candle. From a New Scientist report:

(Stork) also says that given the type of lenses or concave mirrors available at the time, the brightness in the scene would have been reduced around 1000-fold at the canvas, making any projected image all but impossible to see and trace, unless several dozen oil lamps or hundreds of candles lit the scene.

As well as showing that the shadows cast can be plotted back to the candle, Stork's software indicates that the way light rays are reflected off Joseph's head are consistent with the candle being de la Tour's only light source.

The physicist Charles Falco, who collaborated with Hockney on his research, argues back that the artist probably painted the shadows the way they wanted them to look, not how the projector casted them. Link