Although often overlooked, the cost of operating office computer displays can be significant. With annual operating costs of about $10 to $20 per unit, their energy consumption may seem small—but it can add up to thousands of dollars every year for a midsize company. On a national scale, annual office computer monitor energy costs exceed $250 million and account for roughly 4 billion pounds of carbon dioxide emissions. By choosing an Energy Star–qualified liquid crystal display (LCD) monitor, you can significantly reduce your computing energy costs and help shrink your company's carbon footprint.
Two types of computer monitors are available today. Older cathode-ray tube (CRT) technology has been around for decades, but these monitors are bulky, inefficient, and have a relatively short lifetime. Because new flat-panel LCDs (Figure 1) are now cost-competitive and have a number of additional advantages, they account for over 90 percent of all new monitor sales.
In LCD monitors, liquid crystals are sandwiched between thin layers of polarizing glass and are charged by transparent electrodes. Fluorescent tubes located behind or along the edges of the glass layers provide the screen illumination. These efficient light sources are what give LCD displays most of their energy-savings advantages over CRTs. The picture is created by varying the voltage across the electrodes, which causes the crystals underneath to change orientation. As the fluorescent light travels from behind the screen to your eye, the different orientation of the charged crystals in relation to the polarized glass layers produces different colors and brightness levels. By controlling millions of individual crystal cells, or pixels, in this way, an LCD monitor is able to create images by simply changing the voltage pattern.
LCD technology allows for greater flexibility than CRT technology. Because the footprint is about half as large, these monitors can fit into tighter spaces. And unlike CRT technology, for which screen size was limited to about 21 inches, LCD monitors can be much larger—making them an ideal option for workers who can benefit from larger screen sizes, such as graphic artists and web designers.
As older CRT monitors near the end of their usable life, an LCD monitor is the best choice for replacement in most applications. Over the course of its lifetime, an LCD monitor will save more than $100 in energy costs compared with a competing CRT monitor, and it will last nearly three times as long (Table 1).
LCD and CRT monitors are available in similar sizes, but buyers should be aware that monitor measurements are different between the two technologies. For example, a 15-inch diagonal LCD monitor has about the same size viewing area as a 17-inch CRT monitor.
When shopping for a new monitor, it's important to realize that not all LCD displays are created equal. The long-term energy savings from choosing an Energy Star–qualified model will often outweigh any initial price difference. To qualify for Energy Star status, a monitor must operate below a certain active power threshold determined by its screen resolution. For small screens, the power draw must not exceed 23 watts; medium and large monitors must not draw more than 28 watts per million screen pixels.
For example, a typical 17-inch LCD monitor has a pixel resolution of 1280 x 1024, which translates to about 1.3 million pixels, or 1.3 megapixels (Table 2). To meet Energy Star criteria, this model must therefore use 37 watts or fewer in active mode. By comparison, some non–Energy Star LCD models consume twice as much—barely better than a CRT.
To qualify for Energy Star status, the monitor must also be capable of initiating low-power mode when the user steps away or stops working. Also, many people don't realize that computers and monitors consume energy even in "sleep" and off modes; Energy Star monitors must minimize power draw in these modes as well (Table 3).
Currently there's no Energy Star certification for the largest LCD displays, but in June 2009, new standards that apply to large "professional displays" of over 30 inches (diagonal) are slated to take effect. For the latest minimum standards and qualifying products, see Energy Star's Monitors web site at www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=MO. No CRT monitors currently on the market are efficient enough to qualify for Energy Star status.
Power consumption is closely related to screen size in computer monitors. An average 19-inch LCD monitor consumes nearly double the wattage of a 15-inch model. So even if you go out of your way to purchase a high-efficiency model, it could yield little savings if not sized appropriately for your application.
- Did you know that when your screen saver is running, the monitor is not "sleeping" but using the same amount of electricity as if you were working away on a spreadsheet or your resume? To save energy while your computer is idle, make sure that your monitor's power-management settings are enabled.
- Turn monitors off at night, on weekends, and whenever they're not being used for extended periods. Your energy costs will more than triple if you leave monitors on continuously.
- In recent years there have been widely circulated claims that using a search engine with a black background or setting application backgrounds to darker hues would save a significant amount of energy. Although this is true for old CRTs, the fluorescent backlights in an LCD monitor are on regardless of what colors are being displayed and yield no significant energy savings when you alter colors.
- Shortening the delay time before your monitor automatically powers down into sleep mode can yield significant savings.
- Software available from a number of vendors allows organizations to control the power-management settings for all networked computers from a single administrative work station. For organizations with hundreds or thousands of computers, the energy savings from centralized control can be significant. For more information, refer to the Purchasing Advisor on Computer Power Management Software.
In 2008 and 2009, Energy Star will revise its current regulations. New and more stringent regulations are expected to take effect in June 2009.