iPhone 5 - Backlight turns off when I get a text

I have been having an issue with my backlight turning off completely when I receive a text message on my iPhone 5. It is very random. It doesn't happen every day, just once in a while. My screen will be completely off, then it will fully light up when I get a text message, then 1-2 seconds later the backlight will go off completely but the screen will remain on. I don't have auto brightness or anything like that turned on.

Any ideas what might be causing this or how to fix it?

Thanks!