Backlight works for a moment then turns off?

I was using my phone, specifically I had just turned off cellular data which should be completely unrelated, then the backlight just turned off. The screen became completely dim. The phone was not hot, there was obviously no water either. Now when I power the phone off and back on, or lock or unlock it, the screen is bright for a moment and then dim. This seems to indicate that the screen is working, but I would guess it's a software issue? I've tried searching for solutions but all the solutions I could find are for backlights that are not working, not ones that work for a moment then stop. I don't think it's a loose connection, because when I start it it works for the same amount of time, just a moment, even if I place it still on a table, with no shaking to cause a connection to break. I have tried turning off automatic brightness, moving brightness off and on, powering off and on, using reset all settings, and I have even erased and restored from backup. Any other ideas? It seems unlikely to me that this is a hardware issue, why would it work for a moment and then not, if it was a bad light?