Dark Mode (or dark background mode, night mode) has long been one of the favorite features on smartphone, laptop devices, etc. Not only by helping the eyes of the user suffer from fatigue. when operating at night, it also helps the device save more battery, especially for devices that use AMOLED screens.
Even so, there are still controversies around this issue. While using the Dark Mode on the AMOLED / OLED screen makes the battery saver more proven, the question here is whether black pixels really save battery power compared to points. Gray photo?
Not to mention the question of which pure black or gray interface looks better, in this article, XDA-Developers programmer Dylan Raga will help us find the answer to this problem, all However, some basic knowledge of OLED screen operation will be needed.
How OLED panels work
Unlike LCD base panels that use a backlight to illuminate the entire screen, with OLED panels (Organic Light-Emitting Diode), the pixels will automatically glow separately. Each pixel will consist of three basic colors: red (red), green (blue) and green (green), and these pixels will display the colors needed at a certain brightness depending on the amount of power is transmitted. Each color is created by mixing three basic RGB colors at different light intensities, and white itself is a combination of the three RGB colors above, while black is created by turning off These 3 RGB colors are completely.
Pixel matrix on OLED screen arranged vertically
What about dark gray? Gray, dark gray and light gray are actually only different in shades of white. A gray pixel is created by creating a white pixel and then reducing the voltage corresponding to the percentage based on the brightness level that the pixel needs.
Can be visualized using RGB color code, such as color # ffffff / rgb (100%, 100%, 100%) is pure white, # 000000 / rgb (0%, 0%, 0%) is pure black, and gray will be a set of RGB colors with the same light intensity as # f0f0f0 / rgb (94.1%, 94.1%, 94.1%) good # dedede / rgb (87.1%, 87.1%, 87.1%). The OLED screen will use the input code of the color to be reproduced with the parameters of each color and then adjust the voltage to produce the corresponding color.
The gray scale in the Color Picker panel
When reconstructing the colors to display, the OLED screen will need to go through another step, which is the "gamma correction" step. In this article we will not explain too much about gamma correction, however, it is easy to understand, gamma correction will take linear color code values ranging from 0% to 100%. then accumulate on a certain number. The current gamma calibration standard uses 2.2 exponent, so each input color parameter will be exponential to 2.2 and the result will be the brightness of the corresponding RGB color when displayed.
How much electricity does the gray pixel cost?
Take for example the Google Material Dark Theme interface using color code # 121212 / rgb (7%, 7%, 7%). After adjusting gamma (0.07 ^ 2.2) we get 0.3%, which means that the gray color that Google uses for the Dark Theme interface is 0.3% brightness compared to the brightness of pure white.
Gray is used by Google compared to black completely
As mentioned above, the brightness of an OLED pixel depends on the voltage applied. That is to reproduce the dark gray, the device only needs to transmit 0.3% of the voltage it uses to reproduce white. Of course "0.3% of gray will still be more than 0% of black".
Yes, to better understand, we measured the luminous efficiency of the screen on the OnePlus 7 Pro (at 60hz scanning frequency) by using linear regression from drawing device power graphs. compared to the brightness of the output screen, in two modes is black display and screen off, and compare the results. The device's screen will still consume power only by switching on, because the monitor driver must be active and ready to send / receive signals to the processor. The results show that the screen of the OnePlus 7 Pro consumes 400mW and adds 4mW per nit (brightness unit).
Graph of correlation between brightness and device capacity
We assume the screen brightness is 100 nits for pure white display so that the calculation is easy. At this white level, OnePlus 7 Pro will consume 400mA + (4mW / nit × 100 nits) = 800mW. When displaying the entire black color, the screen of the machine will consume a basic energy level of 400mW. As for dark gray, due to the 0.3% brightness compared to white, the screen will consume 4mW / nit × 0.3 nits = 1.2mW. So when the entire gray is displayed, the screen of the OnePlus 7 Pro will consume 1.2mW more than when displayed in black.
In summary, in theory, displaying dark gray will consume an insignificant amount of energy compared to the whole black display. However, many people will assume that it is only in theory. Therefore, we will go into actual measurements.
Measure actual usage time
We set up the screen of the OnePlus 7 Pro at 100 nits of brightness using a metering meter, and then let this screen show the full screen of the photos only in white, black and dark gray, each in within 5 minutes and measure the total power consumption. Since the screen of the OnePlus 7 Pro has gamma correction higher than the standard in the dark area, so with the display brightness for color # 121212, the above 0.3 nits value will be replaced by 0.18 nits, which means The screen of the OnePlus 7 Pro even consumes less power when displaying dark gray in fact.
Display white at 100 nits brightness
When the screen of the OnePlus 7 Pro is displayed in white at 100 nits brightness, the total power consumption of the device is at 1000mW after 5 minutes, while for black, the device consumes 600mW of energy and for color dark gray fluctuates at 600mW – 610mW. These figures are not different from the theory we calculated above. And the difference of about 10mW when displaying dark gray does not seem to come from the screen but from other things, like waves, underground tasks or something that we have not been able to identify.
At a voltage of 4.03V (average for one device), 10mW corresponding to the average intensity will be 2.5mA. With the 4000mAh battery of the OnePlus 7 Pro, this means the Dark Mode interface with dark gray tones will consume 0.063% of the device's power every hour. In other words, Full black use on the OnePlus 7 Pro will save an additional 2 seconds of battery life.
The result is probably not too surprising when we have shown from the beginning based on theoretical numbers. Hope you have your own answer.