CALIFORNIA: Apple released iOS 9.3, the latest version of its iPhone and iPad software – including a much-anticipated night mode. The free update is available for all iPhones and iPads currently running a version of iOS 9, including the iPhone 4S, iPad 2 and iPad mini or newer. The biggest change in the new version is the addition of Night Shift, a mode that reduces the amount of blue light emitted by the screen. Certain wavelengths of blue light are thought to disrupt your circadian rhythm by tricking your body into thinking it is still daylight outside. That makes it harder to fall asleep. By tuning the display colours to a warmer, more reddish tone, it reduces the amount of blue light emitted and should, in theory, reduce the impact of looking at an iPad or iPhone screen before bed. Night Shift can kick in automatically at sunset and start reducing blue light until the morning, when it restores the natural colour balance of the screen.