How to enable LED notifications on your iPhone
Go to Settings, General, Accessibility and find LED Flash for Alerts.
Once you enable this feature your iPhone will now flash anytime you receive an alert.
It uses the iPhone’s LED light (used for flash and flashlight) to notify a user whenever a new alert has been received. This was created with the hearing impaired in mind, but it is helpful for anyone that wants a more noticeable alert than simple vibrations or tones.