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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)?

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wonderich
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2 Answers2

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An LCD panel has a background illumination which is always on if the panel is on and uses the same amount of energy regardless of what is displayed. The only way you can save energy is by dimming the panel which will dim the background illumination but not by displaying something black. The night mode is (today) primarily intended to go easy on your eyes.

For a CRT display, the story is different. There the cathode ray sweep the screen very fast, modulating its intensity to match the desired brightness. Displaying something black will save energy. That's also why CRT give blacker blacks. What you see is really no light, not just light absorbed by the liquid crystal matrix.

I should mention however that as a general rule, CRTs use way more energy than LCDs.

I'm not sure about plasma and/or OLED displays. Maybe somebody else can shed light on this (no pun intended).

Jonas Greitemann
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Oled uses less energy in night mode since your screen is being lot per pixel if it is old, the black pixels use no light

user111282
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