The iOS 9.3 software update includes Night Shift mode that helps users get a good night's sleep by reducing the amount of blue light emitted from a backlight of their iOS device.
Night Shift is unavailable when an iPhone is in Low Power Mode and a workaround that let you ask Siri to activate Night Shift in this mode no longer works.
As first reported on by 9to5Mac's Jeff Benjamin, asking Siri to enable Night Shift while the device is in Low Power Mode now yields a warning message.