Screensavers: The truth
Myth: Screensavers save energy.
Reality: Screensavers do not save energy. Rather than “saving” your screen from energy usage, screensavers were designed in the old days of cathode ray tubes (CRTs) to prevent an image from “freezing” onto the screen. Screensavers are not only unnecessary on modern LCD screens, but they are also more energy intensive. Screensavers can burn up to twice as much energy as when left in the active screen because they prevent your computer from entering sleep mode and are often graphics-intensive.
What is a screensaver?
A screensaver is a type of computer program initially designed to prevent phosphor burn-in on CRT and plasma computer monitors by blanking the screen or filling it with moving images or patterns when the computer is not in use. Contemporary screensavers are used primarily for entertainment, security or to display system status information.
Purpose
Before the advent of LCD screens, most computer screens were based on cathode ray tubes (CRTs). When the same image is displayed on a CRT screen for long periods of time, the properties of the exposed areas of phosphor coating on the inside of the screen gradually and permanently change, eventually leading to a darkened shadow or "ghost" image on the screen. Cathode ray televisions, oscilloscopes and other devices that use CRTs are all susceptible to phosphor burn-in, as are plasma displays to some extent.
Screen-saver programs were designed to help avoid these effects by automatically changing the images on the screen during periods of user inactivity.
For CRTs used in public, such as ATMs and railway ticketing machines, the risk of burn-in is especially high because a stand-by display is shown whenever the machine is not in use. Older machines designed without burn-in problems taken into consideration often display evidence of screen damage, with images or text such as "Please insert your card" (in the case of ATMs) visible even when the display changes while the machine is in use. Blanking the screen is out of the question as the machine would appear to be out of service. In these applications, burn-in can be prevented by shifting the position of the display contents every few seconds, or by having a number of different images that are changed regularly.
Modern CRTs are much less susceptible to burn-in than older models due to improvements in phosphor coatings, and because modern computer images are generally lower contrast than the stark green- or white-on-black text and graphics of earlier machines. LCD computer monitors, including the display panels used in laptop computers, are not susceptible to burn-in because the image is not directly produced by phosphors (although they can suffer from a less extreme and usually non-permanent form of image persistence). For these reasons, screensavers today are primarily for decorative/entertainment purposes, or for password protection. They usually feature moving images or patterns and sometimes sound effects.
Considerations
Monitors running screensavers consume the same amount of power as when running normally, which can be anywhere from a few watts for small LCD monitors to several hundred for large plasma displays. Most modern computers can be set to switch the monitor into a lower power mode, blanking the screen altogether. A power-saving mode for monitors is usually part of the power management options supported in most modern operating systems, though it must also be supported by the computer hardware and monitor itself.
Additionally, using a screensaver with a flat panel or LCD screen instead of powering down the screen can actually reduce the lifetime of the display, since the fluorescent backlight remains lit and ages faster than it would if the screen were turned off completely. As fluorescent tubes age they grow progressively dimmer, and they can be expensive or difficult to replace. A typical LCD screen loses about 50% of its brightness during a normal product lifetime, if left on continuously. (In most cases, the tube is an integral part of the LCD and the entire assembly needs to be replaced.)
Thus the term "screen saver" is now something of a misnomer—the best way to save the screen (and also save electricity) would simply be to have the computer turn off the monitor.
Notice also that screensavers may utilize a significant amount of CPU time, increasing power consumption in the process.
Energy Vibe. April fooled: Energy myths dispelled http://www.energyvibe.com/archives/2013/april-fooled-energy-myths-dispelled
Wikipedia: http://en.wikipedia.org/wiki/Screensaver
