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For LCD screens it doesn't matter. They use the same amount of power whether the screen is black or white. There's no way to damage the screen by displaying an image.
OLED displays are vulnerable to burn in. So a bright static image left on screen for a long time can result in a latent image that's permanently burned into the screen. That's because the OLEDs degrade faster when they're brighter. But a black screen should have no effect.
Strictly speaking, all screens will experience decreasing LED brightness as a function of hours on and brightness level. Modern LCD displays use LEDs for backlighting, so they will get dimmer over time if you leave them on (regardless of what they're displaying). But because the LEDs are all running at the same power level, they'll all degrade at the same rate, so no images getting burned in
just the display as a whole slowly getting dimmer over time.
OLEDs have that happen because different parts of the display will dim at different rates, depending upon what's shown on-screen, because each pixel is a different LED that can be run at a different brightness level.
There are some LCD displays that can have different levels of backlighting for different parts of the screen at one time ("local dimming"), and I guess that theoretically, that could result in burn-in of big rectangles on the screen, though I haven't read about this actually happening or people measuring it.
https://en.wikipedia.org/wiki/Backlight
Most LED backlights for LCDs are edge-lit, i.e. several LEDs are placed at the edges of a lightguide (Light guide plate, LGP), which distributes the light behind the LC panel. Advantages of this technique are the very thin flat-panel construction and low cost. A more expensive version is called full-array or direct LED and consists of many LEDs placed behind the LC panel (an array of LEDs), such that large panels can be evenly illuminated. Full-array local dimming is often abbreviated as "FALD". This arrangement allows for local dimming to obtain darker black pixels depending on the image displayed.
https://displayhdr.org/lcd-dimming-in-hdr-displays-explained/
2D or Full array local dimming (FALD): In this design the backlight LEDs are moved from the edge of the panel to the rear of the panel and are arranged in a two-dimensional matrix of LEDs. Each LED is independently controlled and adjusts the brightness of just one “square of a checkerboard” on the display, although typically they are rectangles rather than perfect squares. Today’s HDR displays and televisions typically have between 384 and 1152 zones. These designs are the most expensive, due to the complexity of the circuitry and the processing demands required. The design can also generate a large amount of heat, and often requires cooling fans and/or heat sinks to be placed behind the LCD panel to draw heat away from the display electronics. Full array local dimming produces the best image quality of all of these designs and can achieve simultaneous contrast ratios of 20,000:1 to 500,000:1. Due to the high cost of this design, these displays command the highest prices and typically cost thousands of dollars.
Why not let it shut off the screen, which is enabled by default?
Any screen can experience burn in.
Black is better than anything else, off is best. See if there's a key combo for your laptop to turn off the display
It depends on the type of screen. LCD or OLED? No. Just have the screen turn off after a minute or two through the power settings if you need the whole machine to continue running.
