The technical term for the lights on the front of your Brother machine is Light Emitting Diodes (LED's).
This FAQ explains the meaning of those different LED indications.
Out of Memory (Scan to USB)
The machine’s memory is full and the machine cannot scan the entire document. To clear the error, do one of the followings:
Press any button.
Unplug the machine from the AC power outlet (electrical socket), and then plug the machine in again.
Too Many Files on USB (Scan to USB)
Your machine cannot save to a USB flash drive if it contains too many files. Remove the USB flash drive, press any key, and then do one of the followings:
Delete unused files or folders from the root folder of the USB flash drive, and then try again.
Use a USB flash drive that contains fewer than 999 files.
File Name Cannot Be Used (Scan to USB)
The maximum sequential number for the file name has been reached. Press any button, and then do one of the followings:
Delete unused files from the USB flash drive, and then try again.
Authenticate Error (Scan to FTP)
The FTP user name and password you entered are incorrect or not configured correctly. Confirm that the user name and password are configured or entered correctly, and then try again.
Out of Memory (Scan to FTP)
The machine’s memory is full and the machine cannot scan the entire document. To clear the error, do one of the followings:
Press any button.
Unplug the machine from the AC power outlet (electrical socket), and then plug the machine in again.
Scan Exceeded a Specific Area
The machine has scanned a document that is more than 5000 mm using the Long Paper setting. To clear the error, press Stop.
Pick Up Roller & Reverse Roller Alert
The Pick Up Roller and Reverse Roller Counter have been used over 200,000 times. To clear the error, check the followings:
Pick Up Roller & Reverse Roller Alert & Periodic Cleaning Alert
The Pick Up Roller and Reverse Roller have been used over 200,000 times and the Periodic Cleaning Counter has exceeded the limit. To clear the error, check the followings:
Pick Up Roller & Periodic Cleaning Alert
The Pick Up Roller has been used over 200,000 times and the Periodic Cleaning Counter has exceeded the limit. To clear the error, check the followings:
Reverse Roller Alert & Periodic Cleaning Alert
The Reverse Roller has been used over 200,000 times and Periodic Cleaning Counter has exceeded the limit. To clear the error, check the followings: