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A Guide to HDTVs

[Page 11] Power Consumption

As concern over the environment grows, so do concerns over the amount of energy used by HDTVs, particularly as the screen sizes keep increasing. Consumers are also worried about hidden costs in purchasing an HDTV, and don't want to pay large energy bills for the privilege of watching big-screen content. Manufacturers have responded to these concerns by introducing new technologies which have lowered the power consumption of both LCD and plasma TVs.

Plasma TVs are notably less efficient than LCD TVs. On a plasma each pixel emits its own light, and as resolution and screen sizes, and hence the number and size of the pixels, have increased, plasmas consume more power to create a bright image. On an LCD, since it is the backlight which consumes power to create light, changing the number or size of the pixels filtering the light from the backlight does not have as large an impact on power usage. The backlight on an LCD is also a very efficient and extremely bright source of light, so it too can be increased without consuming large amounts of additional power.

Both plasma and LCD have been subject to constant improvement to reduce their power consumption. On plasma, the introduction of new technology such as Neo PDP has allowed for larger phosphor cells which emit more light at lower power. On LCD, the use of LED backlighting which is more efficient than CCFL backlighting has further reduced power consumption. A range of "Eco" features have also been incorporated into the TVs to reduce average power consumption, such as adjusting the brightness based on ambient lighting, though this can be at the cost of image quality. In short, these changes mean that the latest HDTVs can consume much less power than their predecessors, and the difference between the two technologies is now smaller than it has been in the past.

On both plasma and LCD, the amount of power consumed varies depending on the brightness of the image. Furthermore, the relatively low manufacturer-quoted power consumption figures are usually inclusive of enabling the Eco features, which as noted can reduce image quality. Therefore any real-world comparisons made between the two types of technology needs to be done when the TVs are calibrated to achieve similar optimal levels of image quality and brightness. Comparisons must also be made at similar screen sizes, since larger screens will use more power, all other things being equal.

To see the actual difference, let's compare two CNET reviews of close-performing TVs at the same 55" screen size: the Panasonic TC-P55VT30 high-end plasma, and the Sony Bravia XBR-55HX929 high-end local-dimming LED-LCD. The plasma tested at 133.11 watts default, and 285.63 watts calibrated; the LCD-LED tested at 127.96 watts default and 61.39 watts calibrated. This is a typical pattern for these two technologies - plasmas are generally dimmer at default settings, particularly with the Eco-related options enabled, while LCDs are typically overly bright at default settings. So when calibrated, plasmas tend to use more power, and LCDs use less. They will also both use more power in 3D mode, which requires more brightness to compensate for the loss of light due to the dimming effect of the 3D glasses - see the 3D section for details.

Back to our comparison, and the difference seems very large after calibration: 285.63 watts for plasma vs. 61.39 watts for LED-LCD. When the cost difference is calculated, based on US energy charges of around 11.5c kw/Hr and a usage pattern of 5.2 hours per day, it equates to $62.71 per year for the plasma vs. $13.66 per year for the LED-LCD. Over 5 years it would cost roughly $314 to run the plasma, while the LED-LCD would cost $68; an advantage of $246 to LED-LCD. So despite the improvements, there's still no contest in terms of power efficiency: plasma is notably more costly to run than an equivalent LED-LCD. However when we examine total cost of ownership, the figures reverse. The plasma in our example retails for around $2,125, while the LED-LCD retails for $2,839. Add in the power usage costs and the total cost over 5 years is: plasma $2,439, LED-LCD $2,907; an advantage of $468 to plasma over the 5 year period. Even over a 10 year period the plasma will still be ahead by $291.

This data gives you various options, depending on your priorities:

  • If reducing your carbon footprint is the primary concern, then without a doubt a new LED-LCD is the way to go, and at smaller screen sizes.
  • If ongoing running costs are a significant factor, then in practice the figures are not particularly staggering and either plasma or LED-LCD is fine - whether $62 or $13 a year, we're not talking large sums of money either way. Also keep in mind that if you use your TV for less than an average of 5 hours a day and/or you purchase a screen smaller than 55", the total cost will be less than shown in our examples.
  • If total cost of ownership is foremost in your mind, plasma is significantly cheaper due to its much lower initial purchase price.

  • Importantly, these comparisons don't take into account image quality differences and the various issues discussed throughout the rest of this guide. They also assume the TV will be calibrated; in reality individuals may use dimmer or brighter settings according to taste and viewing environment, which can change the comparisons. You also need to consider the fact that older HDTVs use more power, so even upgrading from an old to a new TV of the same type will yield noticeable improvements in energy efficiency if you don't wish to switch technologies. Finally, if your carbon footprint and general environmental impact are a major issue for you, then energy comparisons are often of secondary consideration because they don't take into account the full impact of the manufacturing methods and the energy used to create these TVs, nor their disposal methods and any long-term environmental harm their components may do.