Darkness is in reality the absence of light. Light we can study, but not darkness. In fact we can use Newton's prism to break white light into many colors and study the various wavelengths of each color. You cannot measure darkness. A simple ray of light can break into a world of darkness and illuminate it. How can you know how dark a certain space is? You measure the amount of light present. Darkness is a term used by man to describe what happens when there is no light present.