Display power consumption
February 1, 2008
Abstract: LCD TVs are about as power efficient (i.e., they consume about the same amount of power per square inch of display area) as CRT TVs. Thus a 50″ LCD TV consumes about 4 times as much power as a 25″ CRT TV. However, LCD monitors are 2 to 3 time more power efficient (i.e., consuming 2 to 3 times less energy per square inch of display area) as CRT monitors.
During a discussion about the popularization of large screen TVs, the claim was made that LCD TVs are much more power efficient per square inch than CRT TVs, largely offsetting the rise in display area to maintain a more-or-less constant total power. I was prompted to try to find information about the matter over the web.
Here are a some relevant documents:
- The BBC reported in December 2006 that there is some controversy about the relative efficiency of CRT, LCD and plasma TVs.
- Mr. Electricity has it that 17″ CRT monitor uses 80 watts, while a 17″ LCD monitor uses 35 watts.
- HP s7540 17″ CRT monitor uses 64 watts.
- HP Compaq FS7600e 17″ CRT multimedia monitor uses 75 watts.
- A 2005 NRDC study on the Energy Star website shows that CRT TVs are as power efficient as LCD TVs or even somewhat better, that plasma TVs are about power efficient as LCD TVs and that projection TVs are the most efficient (chart on page 5).
- A 1999 Home Energy Magazine article gives quite low power consumption numbers for CRT TVs, based on a large sample of units. TVs 18″ or smaller average 47 watts, and even 19-20″ average 68 watts.
- A comprehensive specifications list on cnet.com shows LCD TVs as consuming 0.25-0.35 watts/inch2, plasma TVs about 0.3-0.4, while projection TVs consume 0.11-0.17 watts/inch2.
- Cornell professor Alan Hedge claims ,based on a 1998 cost analysis study for call centers, that LCD monitors “can reduce display energy use by some 60%”.
I then utilized my Kill-A-Watt power monitor and with the cooperation of friends I was able to obtain some readings of power consumption on specific displays (TVs and computer monitors). The results are in the table below.
The apparent conclusions emerging from the table and from the information in the links above are as follows:
- For some reason, CRT monitors are much more power intensive (in watts per sq inch) than CRT TVs (a factor of two typically, but up to a factor of 4).
- LCD displays are about as power efficient as CRT TVs. They are, thus, a power saver as a replacement for CRT monitors, but not as replacements for CRT TVs. Large LCD TVs are larger power consumers than the smaller CRT TVs.
- The single plasma screen measured is almost twice as power intensive as the LCD displays.
- The highest efficiency display is the LCD projection TV, which is about a third more efficient than an LCD display.
|Dell 2407WFP 24″||LCD||62||20.50||12.75||261||0.24|
|Dell 3007WFP 30″||LCD||94||25.00||16.00||400||0.24|
|NEC Multisync-FE-1250 20″||CRT||93||15.75||11.75||185||0.50|
|ViewSonic P810 19″||CRT||92||15.00||11.25||169||0.55|
|Sony Trinitron-Wega 27″||CRT TV||100||21.60||16.20||350||0.29|
|Phillips 27″||CRT TV||80||21.60||16.20||345||0.23|