The steady increase in CMOS imager pixel count is built on the technology advances summarized as Moore's law. Because imagers must interact with light, Moore's Law impact differs from its impact on other integrated circuit applications. In this paper, we investigate how the trend towards smaller pixels interacts with two fundamental properties of light: photon noise and diffraction. Using simulations, we investigate three consequences of decreasing pixel size on image quality. First, we quantify the likelihood that photon noise will become visible and derive a noise-visibility contour map based on photometric exposure and pixel size. Second, we illustrate the consequence of diffraction and optical imperfections on image quality and analyze the implications of decreasing pixel size for aliasing in monochrome and color sensors. Third, we calculate how decreasing pixel size impacts the effective use of microlens arrays and derive curves for the concentration and redirection of light within the pixel.