I was calling following function which give error
[mDevice setTorchModeOnWithLevel:0.5 error:error];
The reason of error was that I have not included AVFoundation library in build setting. After including my error resolves @rakeshNS we can dim the zbar sdk light by using
AVCaptureDevice *mDevice = mReader.readerView.device;
[mDevice setTorchModeOnWithLevel:0.5 error:nil];
Thanks to everybody