In 1905 Albert Einstein showed that light must be composed of particles, since it was the only way to explain the “photoelectric effect,” where light impinging on a metal ejected electrons from it. This contradicted the long-held premise that light was a wave phenomenon, as first shown by Thomas Young in 1804, since it was the only way to explain the “two-slit interference pattern” produced when light passed through a light-blocking substance containing two slits. These two ways of describing light are incompatible, not only because neither can explain the other’s phenomenon, but also because particles are tiny objects with a unique location and mass, whereas a wave has neither a unique location nor mass and is an oscillation in a medium of some kind such as water or a musical instrument string. How light can actually be one or the other or both at the same time (!) will be described in a proposed 90-minute lecture on this topic by Frank Levin, a retired Brown University physics professor. Like his RWA courses on cosmology and global warming, the lecture will be for persons with neither a math nor a science background, just an interest in the topic