Models help us understand processes we can't visualize. Light has two primary models or theories, the particle theory and the wave theory. Newton believed in the particle theory, while Huygens was a wave theory proponent. The destructive and constructive interference patterns shown by Young's double slit experiment reinforced the wave model. Maxwell proposed that light is an electromagnetic wave, part of the EM spectrum. Hertz produced radio waves as part of the EM spectrum. It seems like wave theory had the edge, until Einstein and his quantum theory of light.