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.
Model Type Power Width Height Area Power density
    Watt Inch Inch Inch2 Watt/ Inch2
Dell 17″ LCD 22 13.25 10.50 139 0.16
Dell 2407WFP 24″ LCD 62 20.50 12.75 261 0.24
Dell 3007WFP 30″ LCD 94 25.00 16.00 400 0.24
Dell 20″ LCD 56 16.00 12.00 192 0.29
NEC Multisync-FE-1250 20″ CRT 93 15.75 11.75 185 0.50
NEC 15″ CRT 104 11.25 9.00 101 1.03
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
Panasonic 44″ LCD-proj 150 39.00 22.00 858 0.17
Samsung 50″ Plasma 420 43.50 24.50 1066 0.39
Phillips 27″ CRT TV 80 21.60 16.20 345 0.23

10 Responses to “Display power consumption”

  1. Jill Says:

    What content was on the sets while you were measuring? That can make a difference for plasma & CRT.

  2. yoramgat Says:

    Hi, Jill.

    My presentation here is somewhat of a simplification: there are several factors influencing the power consumption of display devices. One of them is content, as you point out. Others are the various settings of the devices (brightness, contrast, etc.)

    For the monitors, LCD and CRT, I used the desktop view with the standard MS-Windows XP background (rolling hills landscape). With what little experimentation I carried out, I did not see much difference depending on content.

    For the TVs, the reading was averaged over some time of regular TV content. (The Kill-A-Watt monitor allows you to measure the total power consumed over a period of time.)

    The settings for all the devices were not tweaked – they were used as they are normally used by their owners. I guess that in most cases, the factory default settings were used.

  3. prasad Says:

    i want to know –
    is there any difference between power consumed by CRT monitors ant LCD monitors?(having same screen area).
    please reply to this query.
    thanking you in anticipation.

  4. yoramgat Says:

    Hi prasad,

    The answer to your question is in the abstract above: “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.”

  5. Janet Says:

    I assume your tests used the speaker system with the TV and not additional speakers, correct?

  6. yoramgat Says:

    Hi Janet,

    Yes. I believe that all the TV measurements (taken by friends rather than me personally) account only for the power of the TV set itself, with the built-in speakers on at normal listening volume.

  7. Mukti Ray Says:

    I wish to know the power cunsumption of a 29inch Sony Wega TV whwn Sound is minimum and when sound is midway.
    Do you have any data on power consumtion of a simple microwave oven running at 700w(display) for 10 minutes.
    thanks mukti

  8. […] yourself with a handy power meter, such as P3’s Kill-A-Watt. Someone did this with their monitors and found some interesting results. For more televisions, CNet has a handy HDTV power consumption […]

  9. Engineer Says:

    Here is the reason why the power used by an LCD is greater per square inch, than the power used by an CRT-type TV: the resolution of the LCD is a lot greater. That means there are a lot more pixels (color dots) per square inch on the LCD. Each pixel needs energy to light up. The old CRT-type TVs have a resolution of 648×486 pixels at most, while LCDs have lots more. The 1080p type that everyone wants these days has 1920×1080 pixels. Also, old TVs were interlaced, so only half the pixels were lit up at one instant, while modern LCDs will light up every pixel (well, unless they are showing black, of course). So that means more power consumption, too. The newer LED types use less energy per pixel, so a lot less engery per square inch.

  10. Yoram Gat Says:

    Hi Engineer,

    I don’t see a direct connection between screen resolution (or temporal resolution) and power consumption – there may be some relation but it is not obvious to me why or how. In theory, lighting up 1 large pixel should take as much energy as lighting up, say, 4 pixels whose total area is equal to that of the single large pixel. This is the reason why the comparison is made in terms of power per area rather than power per pixel.

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