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Sony reveals the Xperia Z5 Premium’s secret: It only shows 4K when you actually need it

Sony’s new Xperia Z5 Premium is gorgeous, and the 4K (well, UHD) resolution screen a technically amazing achievement. However, many question how Sony will get the device to reach the quoted two-day battery life with such a high pixel count. Now we know why. The Xperia Z5 Premium only fires up all 3840 x 2160 pixels when you’re watching 4K video, or viewing images. The rest of the time, the screen’s showing at 1080p.

In a statement provided to PhoneArena, Sony says: “The Xperia Z5 Premium features a 4K display with a resolution of 3840×2160 pixels based on SID Standard and enables all video and image content to be enjoyed in 4K resolution. All other content is displayed at 1080p or lower resolution in order to optimize the performance and battery stamina for this device, ensuring you can enjoy the 4K resolution when you need it most.”

Related: Hands-on with the Sony Xperia Z5 Premium

The Z5 Premium has a big 3430mAh battery inside, and in our hands-on test of the phone, we noted a two-day battery life seemed plausible after checking the battery usage meter on the device. While some may feel cheated that not all 3840 x 2160 pixels will be lit up at all times, it’s a very clever way of delivering high-res performance when we actually need it, without sacrificing a sensible standby time. The automotive industry has been doing something similar for years, creating big engines that run on fewer cylinders to conserve fuel, and only unleashing all of them when you step on the gas.

Sony announced the Z5 Premium alongside the Xperia Z5 and Z5 Compact, both of which have a fixed resolution screen — 1080p and 720p respectively. The phones are expected to go on sale near the beginning of November in the UK, but we’re still waiting to hear if any of the three phones will come to a U.S. network.