Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light.In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models.
Answer Viruses
I believe the answer is viruses because viruses destroy and attack cells. Also they invade bodies. Hope this was helpful :)
