The algorithm considers a virtual light source producing excitation light that illuminates the object. This casts shadows either on parts of the object itself or on other objects below it. The interaction between the excitation light and the object provokes the emission light, that also interacts with the object before it finally reaches the eye of the viewer.
H. T. M. van der Voort, G. J. Brakenhoff and M. W. Baarslag. "Three-dimensional visualization methods for confocal microscopy", Journal of Microscopy, Vol. 153, Pt 2, February 1989, pp. 123-132.