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LED backlight a likely culprit in iPad heat issue, says expert

The new iPad has twice as many LEDs as the iPad 2, which means more heat from those LEDs and from the battery, a display expert tells CNET.

Brooke Crothers Former CNET contributor
Brooke Crothers writes about mobile computer systems, including laptops, tablets, smartphones: how they define the computing experience and the hardware that makes them tick. He has served as an editor at large at CNET News and a contributing reporter to The New York Times' Bits and Technology sections. His interest in things small began when living in Tokyo in a very small apartment for a very long time.
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Brooke Crothers
2 min read
Apple

Reported heat issues with new iPad are most likely due to a combination of more backlights and more power needed to drive the backlights, an expert told CNET. This follows a CNET report attributing extra heat to the new iPad's A5X chip, also.

Apple has doubled the number of LEDs in the new iPad to achieve the same brightness as the iPad 2, driving up power requirements and therefore heat, Raymond Soneira, president of DisplayMate Technologies, said in a phone interview today.

"The LED power at maximum brightness is 2.5 times that of the iPad 2," Soneira said. "They had to jack up the number of LEDs so the peak brightness is the same as on the iPad 2. That absolutely makes it warmer," he said, adding that the new iPad didn't get uncomfortably warm in his testing, though.

Soneira offered four reasons the new iPad runs warmer:

    1. Twice the LEDs: That means more heat coming from more LEDs. This is especially a problem at full brightness.
    2. 2.5X the power needed: The brightness efficiency is lower because the new iPad has more pixels (which means more transistors) compared to the iPad 2. More pixels and transistors take up more space, meaning less opportunity for light to pass. "So they basically have to blast light through the LCD to make it come out." Soneira adds: "I measured the LED power at maximum brightness--it's two and a half times greater than on the iPad 2."
    3. Battery generates more juice: The battery has to push out more power. This makes the battery warmer.
    4. Traditional LCD technology: Sharp's power-efficient IGZO technology was not ready for the new iPad. That forced Apple to use traditional--and less power efficient--amorphous silicon tech.

      And heat isn't the only issue. The new iPad's battery will run down faster at full brightness, Soneira said.

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      "So, not only do the LEDs need two and a half times more power but the battery is going to run warmer.... Look at it this way, the [power draw of the] LEDs is 2.5X compared to the iPad 2, and the battery is 1.7X [larger]...so what happens is that if you run your new iPad at full brightness, the battery run time is less because you only put in 70 percent more battery but you're using 150 percent more power."

      The iPad's new A5X chip packing quad-core graphics may also contribute to a warmer iPad. That new chip is faster and larger, which typically leads to more heat, as CNET reported earlier.

      See DisplayMate Technologies' report on the new iPad's display.

      And note that CNET Labs is investigating the problem too.

      Updated at 4:05 p.m. PDT: adds Apple A5X chip-related discussion.

      Updated on March 21 at 2:55 p.m. PDT: corrects that "power draw of the LED" is 2.5X. So, the new iPad has 2X the LEDs of the iPad 2 but 2.5X the power consumption.