This lecture discusses the average values and uncertainties associated with photons, focusing on the mathematical formulations of mean and variance. The instructor presents the concepts of amplitude and intensity uncertainties, emphasizing the relationship between them through Fourier analysis. The lecture covers Heisenberg's uncertainty principle and its implications for photon behavior, including coherence and interference phenomena. The instructor explains the significance of coherent and incoherent light sources, particularly in the context of interferometers like the Michelson and Mach-Zehnder setups. The discussion extends to optical coherence tomography and the importance of coherence length in various applications. Exercises are included to illustrate practical applications of these concepts, such as calculating average positions and analyzing the behavior of single photons in beam splitters. The lecture concludes with a review of the Crookes radiometer experiment, demonstrating the interaction of light with matter and the resulting motion of the device.