NEC AccuSync AS221F-BK 21.5" 16:9 IPS Monitor - Manual (Page 8)

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Image Persistence
Image persistence occurs when a residual or “ghost” image of a previous image remains visible on the screen. Unlike CRT
monitors, LCD monitors’ image persistence is not permanent, but a still image being displayed for a long period of time should
be avoided.
To alleviate image persistence, turn off the monitor for as long as the previous image was displayed. For example, if an image
was on the monitor for one hour and a residual image remains, the monitor should be turned off for one hour to erase the image.
OTEE: As with all personal display devices, NEC DISPLAY SOLUTIONS recommends using a moving screen saver at regular
intervals whenever the screen is idle, or turn off the monitor when not in use.