What does the error message "Light old sensor_state 0, new sensor_state : 128 en : 1" in logcat mean?
They're nothing to do with your app, and they're not really errors. As you might have guessed, they're just reporting changes in the light sensor state. (That's the sensor that controls the screen brightness.)

Samsung ROMs are particularly known for having very 'noisy' log output, owing to Samsung being a little slapdash about software integration. In contrast, Nexus devices tend to have very clean logs, because Google engineers are aggressive about disabling logging when code is committed. You can filter the log messages in Eclipse (or when you use adb logcat on the command-line).