At Insight Media, we are in the midst of writing the "Green Displays Report; The Business Threats and Opportunities of Green Displays." As we were writing the section on emerging technologies, an interesting question came up.

Ken Werner
Senior Analyst and Editor

We would expect a 42-inch AMOLED-TV to be more energy-efficient than a conventional LCD-TV, but how much does that change if the LCD-TV uses direct LED backlighting and local area dimming (LAD)? After all, one reason for AMOLED’s energy advantage is that it’s a self-luminous display, in which light is generated at each pixel location. That means that darker pixels consume less energy than brighter ones, and black pixels consume essentially no energy at all.

Conventional LCD-TVs, on the other hand, use a backlight behind the LCD to generate their light. The light is on at all screen locations, with the passage of the light through the screen being controlled at each pixel site. That means a conventional LCD draws the same amount of power whether the scene is dark or bright.

The distinction between these two very different ways of creating an image is blurred a bit when we look at a backlight that consists of an array of LEDs behind the LCDs (direct backlight) that is dimmed section by section (local area dimming) depending on whether the portion of the image that corresponds to that section is dark or bright. This increases the maximum contrast ratio of the display, and also reduces energy consumption. Would a local-area-dimming LCD-TV erase the expected energy advantage of AMOLED?

Getting an answer to this question is complicated by the fact that there is currently a distinct shortage of shipping TVs with white LED backlights and LAD. The Samsung Series 9000 is expected shortly, and Vizio announced an impressive LAD LED-lit LCD-TV at CES, which will best available this fall. Unexpectedly, Sharp has just announced a direct-LED-lit LCD-TV for the coming holiday season, too, but without LAD to cut costs.

So, to get an idea of power consumption for direct-backlit LCD-TVs we need to look at technology demonstrators from recent trade shows.

AT SID, Samsung showed its 46-inch ALPC prototype, which has 2D local dimming and adaptive local boosting (apparently similar to CMO’s "local blasting" technology). Luminance is 550 nits and power consumption typically less than 100w.

At Display Taiwan CMO showed a 55-inch LCD-TV with a novel kind of local dimming that consumed 62 - 90W for four different popular movies. A similar but conventionally backlit system consumed 200W.

Also at Display Taiwan CMO showed its 42-inch Hyper Chameleon "local blasting" LCD-TV. It consumed 77 - 114W to show several different popular movies, while a conventional 500nit comparison panel consumed 170W. A 46-inch AUO edge-lit panel (without LAD, of course) also consumed 170W, but for 450 nits.

All of these numbers are generally consistent. For our baseline, we can say it is reasonable to expect an acceptably bright 42-inch LCD-TV with conventional LED backlighting to consume about 170W, and a similar LAD unit to consume about 85W. LAD makes quite a difference.

Now, let’s compare this with a 42-inch AMOLED-TV, which is difficult since there aren’t any commercial units, and Samsung hasn’t built a technology demonstrator since 2005, and the only way to reliably compare the power consumption of two different TV displays is to run the same programming on both and measure the results.

However, when I asked Barry Young, Managing Director of the OLED Association, about this, he noted that OLED-TVs have consistently consumed 25% to 50% less power when compared with conventional LCD-TVs. He then embarked on an interesting analysis. "[We could] measure the power consumption of the [11-inch AMOLED Sony] XEL-1 running video, which I calculated to be 7.6W. Extrapolating the 11 inches to 46 inches, it would use 133W. The material in the XEL-1 is at least five years old and [the XEL-1] uses a color filter. Assuming it takes 1.5X the power to overcome the loss in the color filter and the material is now at least 2X more efficient; the power would be 45W to 60W for a 46-inch AMOLED."

A reliable source at a leading Taiwanese panel maker told me, "Based on the current light efficiency achieved by OLED material, we estimate AMOLED-TV’s power [reduction] could be 70% of a conventional LCD-TV. As for its comparison over LCD-TV with local dimming, the energy saving may be less than 30%."

If we take the high end of Barry Young’s estimate and compare it with the 85W power consumption of the CMO panel (ignoring the difference between 42 and 46 inches for the moment), we also get an OLED over LAD LCD power saving of 30%.

So, for now, we have an answer to our question. We can expect a large-screen AMOLED-TV to consume about 30% less power than a similarly sized LCD-TV with local-area dimming. That ain’t hay.