Apple, Google and Microsoft: All major manufacturers have built a so-called Dark Mode in their operating systems for smartphones, tablets and computers. Likewise, Facebook is working on such a feature for the Messenger, Google is testing the look in the Chrome browser and WhatsApp will soon get a dark fashion.

The manufacturers promise more pleasant screen work. The "dark mode" should be less tiring for the eyes and help to focus on texts and e-mails. The smartphone battery should also protect the dark screen colors. But what about the advertising promise? We give answers to the most important questions:

What is the dark fashion?

Simply put, bright pixels are dark, dark light. While texts, websites and menus are usually displayed in black on a white background, this is the opposite in dark mode: the font is displayed in bright white, the background is black.

Does the dark fashion spare the eyes?

Anyone who stares at the smartphone display in their youth permanently loses sight, says Claus Cursiefen, director of the Center for Ophthalmology at the University Hospital Cologne. This is clear from studies. But this development has nothing to do with light or dark. "The process of myopia is accelerated by the fact that smartphones are too close to the eye," says Cursiefen the SPIEGEL.

Although there are some studies that may indicate that a contrast reversal like the dark fashion leads to less shortsightedness. But these are very early data from which one can not draw any final conclusions. "There are no serious studies that white writing on a black background is more relaxing for the eyes," says the ophthalmologist.

Also, the Office Eye syndrome, so dry eyes that burn, scratch and itch, can not be avoided with the Dark Mode. The eyes are irritated due to the proximity to the display and the flow of tears is inhibited. "It does not matter if you look at a white, blue or green screen," says Cursiefen.

What really helps: Always interrupt the suture activity on the screen, take a break every half hour and look into the distance, so that the eye winks again often. Children and adolescents are advised to work in the open air for two hours a day in daylight. This reduces the myopia rate by up to 50 percent.

Can Dark Mode save electricity?

It depends on which display one uses. "Dark mode does not do much with LCD displays," says Patrick Schalberger from the Institute of Large-Scale Microelectronics at the University of Stuttgart. The reason: With almost all liquid crystal screens, a light shines constantly behind the display, even if only a few pixels are bright. That always costs the same amount of electricity.

Things are different with OLED displays. With this technology, each pixel itself shines, you can save energy with every pixel that remains dark, says Schalberger: "If only 10 percent of the pixels on the display light up, then I save about 90 percent of electricity." Google's developers have also recognized the savings potential of OLED displays. At a conference in November, they showed that the dark mode of the YouTube app saved about 40 percent and that of Google Maps about 60 percent energy.

The problem: OLED displays are mainly found in high-end smartphones like the iPhone XS. "The electronics are much more complicated at OLED, so the technology is also more expensive," explains Schalberger this circumstance. While you only need one transistor per pixel for LCD displays, up to six times as many for OLEDs. In addition, the effort in the production was significantly greater.

When is the dark fashion worthwhile?

In very dark rooms, it can be more pleasant if the display is not brightly lit. According to Schalberger, the function is particularly helpful when the navigation system switches to dark mode at night, so that you can be less dazzled in the car and can concentrate better on the road.

Otherwise, the users tended to black text on a white background, says the scientist. In the Microsoft operating system MS-DOS, a black background with light text was still completely normal. But already with Windows 95 you could reverse the colors. "There are extremely few people who have really used it," says the scientist. Most of them have stayed with the white background view. The dark mode is therefore a matter of taste.

But to try it once does not hurt. So let's clarify in our photo gallery that you can turn on Dark Mode - or at least something similar - in Windows 10, macOS Mojave, Android 9 and iOS 12.

So the dark mode is turned on

Windows 10 To customize the menus in Windows 10, right-click on the desktop. In the pop-up menu, call up the "Customize" function. A window opens in which the "Colors" option can be selected on the right. At the bottom of the menu, you can set the default app mode to dark.

Windows 10 taskbar, search windows , and menus will be dimmed after the transition. The font color turns white. This does not apply to programs. For example, if you open Word, you must enable dark mode in the Office software settings.

MacOS Mojave In MacOS Mojave, the dark mode is hidden in the system settings under "General". There is a tile that switches between a light and a dark appearance.

MacOS Mojave The menu bar is dark colored and overlaid with white text. However, the change affects only some Apple programs, such as Mail, in addition to the system menus. Third-party programs, such as Word, look the same as they did in Bright mode after the switch.

iOS A real dark fashion is not available in Apple's iOS until version 12. Anyone who still wants to use an at least similar effect, can manage with a trick: In the settings under "General / Accessibility" there is under "Display adjustments" the ability to "invert the colors intelligent". This not only swaps black and white, but also turns blue into orange. In addition, photos and videos are displayed in some apps with inverted colors

iOS If the screen background is then displayed in black, this saves power for the OLED displays of the iPhone X and iPhone XS. However, some apps that actually have a dark background, such as the Sonos app or the camera app Halide, suddenly shine in white.

Android Who wants to run his Android smartphone in the dark mode, needs at least version 9.0. Only with Android "Pie" has Google donated the function to the users. In order to activate the mode on smartphones with an unmodified Android 9, you have to select the menu item "Display" in the "Settings", then scroll down and tap on "Device design". In the selection box, which opens, you tap on "Dark".

Some manufacturers have placed the switch for the dark mode but in other places. In Huawei's case, for example, you can find it in the "Settings" under "Battery" if you scroll down and "Darken the surface colors" is activated.