Cos ϕ. This light has to travel farther than the axial light to achieve a display screen, then it strikes the monitor at another angle ϕ. The web consequence is that the oblique illumination about the screen is scaled-down when compared to the axial illumination via the aspect cos4 ϕ. https://speakers23085.pointblog.net/the-greatest-guide-to-portable-speaker-71561826