Q: iMac screen issue (compensation of ambient light ?)
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Jun 26, 2016 2:36 PMby Johann.B,Hello sl01fr.
Thank you for using the Apple Support Communities. It seems you are encountering some issues with your iMac's brightness when the "Automatically Adjust Brightness" option is selected. I'm happy to provide you with some direction to resolve this.
Let's start by reviewing the following Apple knowledge base articles to ensure everything is setup correctly.
OS X El Capitan: Adjust your display’s brightness
OS X El Capitan: ambient light sensor
Let's also make sure that there is nothing in the way on the ambient light sensor, located next to the FaceTime HD camera on your iMac.
If the issue persists, then let's access Safe Mode and a Test User to check what could be causing it. Here are the articles to complete both steps:
Try safe mode if your Mac doesn't finish starting up
How to test an issue in another user account on your Mac
If the issue persist in both modes, we would then want to reinstall OS X. This should not delete any data, but I recommend backing up your iMac's contents with Time Machine before performing this step. Here are the articles for that:
Use Time Machine to back up or restore your Mac
How to reinstall OS X on your Mac
Make sure to follow the "Reinstall OS X from Recovery" section:
1. Turn on your Mac.
2. Immediately after you hear the startup sound, hold the Command and R keys on your keyboard.
3. Release the keys after the Apple logo appears.
4. If prompted, select a Wi-Fi network, or connect your Mac to the Internet using an Ethernet cable.
5. After the Recovery menu appears, select the option to Install OS X.
6. Follow the onscreen prompts to select your destination disk and install OS X.And lastly, if that fails to resolve the issue, I recommend following the "Erase your drive and install OS X" section of the same article as above. Be sure to check if the issue occurs before you restore your Time Machine backup in order to verify if this is a possible hardware issue with your iMac.
Have a great day.
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Jun 27, 2016 10:16 AMby sl01fr,Hi,
Thank you for your answer. That is a very generalist approach. It doesn't solve the problem. I think the root cause is because my screen is in front of a window. I suppose that the new compensation light mode doesn't work efficiently with a direct light source. In hight luminosity level coming from the window, the screen turns to the max of the brightness and become very blank without any contrast. I have to turn of the auto brightness option an then it becomes normal. I think there is no solution at the moment. It seems that a new option "light compensation" was in the beta of El Capitan and it disappears in the final version. It seems to be integrated now in the auto-light option. May be the issue is due to this new option. See below a screenshot of this option found on the net :
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Jun 27, 2016 2:35 PMby dialabrain,FWIW, First, the screenshot you posted is not of an iMac but an Apple laptop. This is the preference panel for an iMac…
With "Automatically adjust brightness" enabled it is based on the position of the Brightness slider so you may want to adjust the slider to suite your needs. You also have screen adjustments in the Accessibility panel which you can use to adjust contrast etc.…
You have many options available with or without "Automatically adjust brightness" enabled.
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Jun 28, 2016 12:32 PMby sl01fr,Hi,
I just compare my laptop and my iMac, the preference panel are the same. The second option doesn't exists. What I read on forums is that this second option (on the screenshot found on internet) was only in El Capitan beta version. In the final version, it was integrated in the first option. Only one thing is sure, the problem of contrast in high level luminosity appears in the last versions of OS X.
