Cos ϕ. This gentle must travel farther compared to axial light-weight to achieve a monitor, and after that it strikes the monitor at One more angle ϕ. The net result is that the oblique illumination within the display screen is smaller compared to axial illumination by the variable cos4 ϕ. https://brooksznhyl.pointblog.net/little-known-facts-about-fused-silica-reflective-mirror-71137621