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I've got a Dell S23340M - an LCD monitor with an LED backlight, which has built-in options to adjust the brightness & contrast. The monitor features a nifty "Energy Usage" bar that changes as you increase/decrease the brightness. When I increase the brightness, the energy bar goes up quickly but when I increase the contrast, it stays the same (no matter how high I make the contrast).

At 100% contrast, my monitor is practically a giant flashlight but the energy bar still stays the same. I'm wondering if changing contrast actually does anything to energy usage even though the monitor screen seems to be visibly brighter? (If not, why not?)

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    Hi! You wrote about an "LED monitor", which is a confusing and ambiguous term. I edited to clarify. Feel free to re-edit if you disagree. – sleske Oct 2 '17 at 8:42
  • Sorry about that; I'm no tech wiz with monitors lol. The monitor had an "LED" sticker on it so I assumed it was LED. Thanks for the edit! – takanuva15 Oct 2 '17 at 22:17
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Depending on the type of display (and ignoring OLED) I believe that contrast makes very, very little difference to the amount of energy used.

When you are talking about brightness, you are adjusting the lighting source behind the screen - normally high bright LED's or something equivalent. These can draw significant power.

When you are talking about contrast you are adjusting the amount of light filtered through the pixels which make up the front portion of the LED. They certainly do use power, but not as much as the backlight. Remember that human eyes can be deceptive when coming to brightness because the pupils naturally dilate to compensate for different amounts of light depending on the time of day.

OLED based screens are different - they don't use a backlight, and rely on the pixel to produce the correct amount of light - I know that with cellphones which use an OLED display, how dark the background is can make a significant diffence to the longevity of the battery.

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    Pixels don't glow, they block light outside OLED – Journeyman Geek Oct 2 '17 at 3:10
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    Yeah, glow would not be the right terminology. The answer seems mostly on point. But LCD screens operate by blocking light. Turning the contrast up will actually reduce current consumption, but so minimally that nobody would even care. – Appleoddity Oct 2 '17 at 3:37
  • @Appleoddity Different LCDs have different resting states. It's referred to as "normally white" and "normally black". – Agent_L Oct 2 '17 at 15:07
  • @Agent_L thanks. That makes sense. I didn't know that. – Appleoddity Oct 2 '17 at 15:31
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    @JourneymanGeek Pixels glow with a CRT as well... It's only LCD where they don't. – derobert Oct 4 '17 at 19:20

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