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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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closed as off-topic by Kyle Kanos, ACuriousMind, Bill N, Gert, John Rennie Mar 15 '16 at 7:01

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question appears to be about engineering, which is the application of scientific knowledge to construct a solution to solve a specific problem. As such, it is off topic for this site, which deals with the science, whether theoretical or experimental, of how the natural world works. For more information, see this meta post." – Kyle Kanos, ACuriousMind, Bill N, Gert, John Rennie
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Related on Skeptics, Electrical Engineering, Superuser 1, 2, and 3. $\endgroup$ – user10851 Jun 20 '14 at 3:01
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    $\begingroup$ Also Ask Different. (Most of these are LED/LCD/OLED) $\endgroup$ – user10851 Jun 20 '14 at 3:01
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    $\begingroup$ That said, I'm not too sure this is off-topic for us. A general, qualitative question about how devices work (not how to build them, not how to program them, not what studies have been done on them) seems okay. $\endgroup$ – user10851 Jun 20 '14 at 3:06
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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).

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  • $\begingroup$ thanks Jonas, +1. If LCD with dim background is designed to be the black background, I suppose this can save amount of energy? (I am hinting that way may be the environmental-friendly way to go.) $\endgroup$ – wonderich Jun 19 '14 at 22:55
  • $\begingroup$ I would say that the display uses more energy, as the crystal is normal non-blocking, and current is needed to make it black. $\endgroup$ – hpekristiansen Jun 20 '14 at 0:06
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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

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  • $\begingroup$ The second half of your sentence is a little less than clear. Could you add more to this answer? $\endgroup$ – Kyle Kanos Mar 14 '16 at 10:11

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