In some cases, we can enable the Night Mode (reversing the bright and dark color of the display; such as White Text, Black Background) for the screen display.
LCD(Liquid-crystal display) seems to be a common monitor display devise nowadays, so let us consider the LCD at this moment.
(1) Will the Night Mode save more energy?
(2) How can we evaluate the energy efficiency ratio between, for example the Day Mode and the Night Mode?
(3) A bonus question: whether the energy efficiency (of Day Mode and Night Mode) varies for CRT(Cathode ray tube), LCD, Plasma, and OLED(organic light-emitting diode)?