Screen Savers, CRTs and LCDs
Way back when people used cathode ray tube (CRT) based displays, screen savers were essential. Screen savers got their name as they were used to protect the display screen. Cathode ray tubes employed heat to produce images and text. The heat produced by electrons in cathode ray tubes was high and could damage the display if the image on the screen did not keep changing.
The technologies used in LCD displays do not produce much heat when compared to cathode ray tubes, so it's not necessary to use screen savers for LCD displays. As the phosphorus factor (see next section) in LCD displays it is negligible; the chances of them getting damaged are almost zero. You can disable screen savers or better still, turn off the monitor to save energy and to offer better protection for your computer screens.
Older Computer Models
Cathode ray tubes produce images on the screen by hitting on the pixel grids on the back of the screen. The entire screen in a CRT is divided into several grids by intersection of virtual horizontal and vertical lines. Each intersection is termed a grid so the first grid becomes 0H, 0V. Each grid has three dots in a colored display: red, green and blue. The early monochrome displays (green ones) had a single dot per intersection. Any image or text produced on a CRT based display has to be a combination of these dots.
The back of CRT screens are coated with phosphorous materials so when hit, it produces light. When the information about the image to be produced is sent to the CRT, the electron gun contained in the CRT scans the entire screen and employs a cathode ray (a beam of electrons) to hit the predetermined dots to produce the display. Once illuminated, the dots fade away fast. To keep the image constant on the screen, the electron gun strikes the phosphor points again and again on the same dots. The refresh rate could be as high as 60 hits per minute.
Heat causes illumination and thereby, production of images on CRTs, if the same image has to be displayed for a long time, causes the phosphorus to burn, creating permanent damage to the screen. You can identify a burned out CRT as it displays a ghost image even when the monitor is turned off.
To avoid constant hitting of the same phosphor dots, screen savers are used. Because the screen savers contain movements, the cathode rays strike different phosphor dots and helps in preventing burn-out.
Do They Save Energy?
As screen savers are images or text containing movements, your display device constantly works as long as the screen saver is functioning. This means the display would constantly consume the same amount of energy that it consumes when you are actively working on the computer.
Modern Day Displays
LCD displays employ alignment of liquid crystals to create images. The heat emitted in this case is very low when compared to older CRTs and plasma panels. The modern CRTs are less susceptible to burns as they employ multiple phosphorous coatings. Technology has virtually eliminated the need for screen savers by designing displays that can easily sustain heat.
When you use screen savers your display is pretty active and you do not save any energy. Also, the chances of screen damage increases when your display is active for a long time. A blank screen would mean no consumption of power as there is nothing to produce and refresh on the screen. To save on energy and for maximum protection of display screens, it is better to disable the screen saver completely. Turning off the monitor would further save on energy requirements.
Modern day operating systems come with power management options that help you deactivate screen savers and turn off monitors after a specified time period. An ideal time period is anywhere between five to ten minutes.
To turn off your screen saver in Windows, right click on desktop and select Properties (Personalize in Windows 7). On the Screen Saver tab, select None. You can also access power options from the same page.
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Image from Wikimedia Commons/Theresa Knott