Iv seen a thread on here for a app called 1# toolkit or something and apparently you can run the flashlight in background but it doesn't work for me any suggestions ??
Ability to keep the LED light of the camera on in the background may depend on the device. Also, if your phone has OIS, I'd advice not to use the LED as a flashlight since there have been reports that over-using the LED eventually damages the OIS/camera due to undissipated heat.