Help! External display dimmed to an extreme after installing Sierra

[nomtje]

Hello!
I have a problem with my external display; after recently downloading Sierra 10.12.1 with the hope of it fixing my wifi dropping out at random times (it didn't...) my external display (an Acer) became so extremely dimmed that it's pretty much black. I own an macbook air 11" and used the external display to mirror my screen. I use a mac dongle, and it worked just fine before, but now the screen is extremely dimmed when I connect it; when I hold a flashlight close to the screen I can actually see my laptop screen mirrored on the external display, but it's so dark that it pretty much looks black when you look at it normally. Any ideas how I can solve this? Or is this simply a bug that needs to be fixed?

Using the buttons on the display itself to increase brightness didn't work either. It stayed dark.

help!

 

[Nermal]

It sounds like the backlight isn't coming on at all. Did the problem occur as soon as you installed 10.12.1 or a little later?

I would try this: Turn the display off, disconnect it from the computer, then turn it on again. Assuming that it normally displays an "Acer" logo on startup, does that still occur? Can you get into the onscreen menu?

 

[nomtje]

Thank you for your quick reply! While I installed the newer version, my laptop was not connected to the external display so I can't tell if it 'broke' the moment it had successfully installed. I just know that when Sierra was installed and I connected the display to it, it no longer functioned like it had before.

I just checked and I don't see an Acer logo when I turn the display on while it's disconnected from the computer. I have seen this logo before though, while I was trying to get it to work. I remember seeing it since I was worried my display broke so I was relieved to see that logo, since I took it to mean that it's the connection between the laptop and screen that's messed up. Just now, though, I didn't see a logo when turning on the display, both while connected and disconneted from the computer. :/

 

[Nermal]

I suspect that the software update was just a coincidence; it seems that your backlight has died

You could try to do a factory reset, which will probably involve doing what you did earlier: Shining a light onto the screen in order to navigate the menus.