Our low light studio test scene triggers very different exposure values on the cameras. The Sony Xperia Z picks a very slow shutter speed of 1/8 sec which allows it to keep the ISO at 640  but also makes camera shake more likely. The Samsung on the other hand prioritizes faster shutter speeds in order to avoid camera shake and combines a 1/30 sec exposure with ISO 2000. The HTC and iPhone opt for 1/15 and keep the ISO at 445 and 500 respectively. This is still a slow shutter speed for hand-held shooting but at least the HTC offers optical image stabilization to keep camera shake under control. 

Like under the brighter illumination the Sony's image results are disappointing. A combination of noise, noise reduction, sharpening and processing artifacts mean the Xperia Z's image output doesn't look pretty when viewed at a 100% magnficiation. Exposure is good, so social media use and online sharing are not a problem but don't plan on viewing or printing the Sony Xperia Z's images at anything but the smallest sizes.