Why do the brightness and contrast controls on TV's and monitors appear to have the same function?

To the naked eye, they appear to both brighten the image. So, what's the difference between ';brightness'; and ';contrast'; controls on electronics?Why do the brightness and contrast controls on TV's and monitors appear to have the same function?
While they may appear to do the same thing, they are different. The brightness control does adjust the brightness of the image. As the brightness is reduced, the image gets darker. Less light is produced from the screen.





The contrast control adjusts the difference between the dark and light portions of the image. To do this the bright part is darkened some. The image looks flat and washed out. But the final result is less light is produced from the screen.





Because you get less light with both controls, it appears that they do the same thing when in fact they do different things.Why do the brightness and contrast controls on TV's and monitors appear to have the same function?
Contrast deals with the relative *difference* (of lightness) between the dark and the light. Brightness is strictly lighter or darker.