monitor brightness changes after restart with High Sierra 10.13.4

10.13.6 finally fixes this issue! Or rather, the firmware update that's bundled with the software update fixes the issue. I guess they did not have time to finalize the new boot rom for iMac pro before 10.13.5 rolled out. Take a look at your Boot Rom version. It's now 15.16.6059.0.0,0.

By the way, I just ran the delta update, not the combo update, which is not out yet.

Cheers,

Is there an Automatic brightness control in the System Preferences> Display dialogue or ambient lighting control button somewhere. If these are set not to interfere when your Mac starts up then it maybe that a preference file has become corrupted. If In Finder press Shift-Command G enter ~/Library/Preferences/com.apple.systempreferences.plist press Go.

A new Finder window will open up and the file should be highlighted. Move it to the Desktop. Restart a new system preferences plist will be generated open System Preferences> Display and re enter the options you want, Quit System Preferences. Restart, see if it makes a difference.

If that doesn't work then I am not sure, we could put it down to Apples poor coding and quality control of late.

As the Mac starts up it loads the display profile you have set your Mac to use from System Preferences>Displays> Colour. Have you calibrated your display, that is critical for photography, the default settings the Mac uses are often too bright and too blue. You will see there is a Calibrate button on the panel which will let you calibrate the display albeit rather crudely, if you press and hold the option/ alt key down while clicking on the Calibrate button you will get the opportunity to select Expert Mode (again pretty rudimentary), you are guided through a series of procedures to calibrate your display. But nothing beats calibrating your display with an external calibrator and its bespoke software.

Another thing to check is to see if NightShift is coming on and thus altering the colour of your display.

Reformatted the drive. Did a clean install (from recovery). It installed 10.13.4. No change. The screen is still 90 percent brightness on every reboot. Make sure you don't have automatic brightness turned on, as it's enabled by default on new installs.

What Apple told you simply does not make any sense. They just don't know the answer.

Gene

Hi together,

i have the same problem with my iMac Pro. Its funny, but when i check the box for "Automatically adjust brightness" then the slider setting of brightness will be saved. If i turn back the automatic adjustment, the same problem as before. I have posted the problem in the "iMac Pro Forum", hope it helps to sensitize Apple to get going to solve the problem.

Greetings ...

Klaus

I had similar problem - I am running a 2009 i-mac and am using a patched high sierra as my mac is no longer supported officially. My screen was going very dim after and my third party app 'brightness slider' was no longer responding since update 10.13.4. Fixed it by creating the dosdude boot USB drive. booting from that USB and applying the screen bightness patch. my third party brightness app now works again 🙂

June 15th 2018.... Same issue with my Imac Pro. Noticed this a week after getting it and calibrating with my XRite. Calibration brightness does not hold on restart. Also if you have created different profiles and chose a different calibration profile, it will change to the color calibration you created but will not hold the brightness. I just updated to the newest OS version today 10.13.5 and upon restart-same issue persists. My only solve so far has been to screen capture the brightness level at the time of my calibrations, and keep that on my desktop so I can match the proper brightness level for each calibration I have if I restart the system. Very annoying. There are pros like myself who rely on calibration-professional photographers/retouchers etc. and this is unacceptable.

I am using a very primitive way to get around this until they fix it. I have calibrated my iMac pro using color munki. During the callibration process it asks to adjust monitor brightness. After the calibration is done I open the display menu and move it all the way to the left of the screen. I measure the distance of the slider in relationship to the edge of the computer. eg 5.5 inches. On reboot I place it at the same place by measuring it which keeps it still caliberated for my ambient light. I don’t reboot my iMac often. Hope they fix this issue soon.

I have the same exact issue. Was pulling my hair out for a while. But I am seeing more and more reports of this behavior affecting iMac Pros. As far as I know the iMac Pro firmware was not updated by 10.13.4, so this is probably a kext issue.

I have an 8-core base model. After updating to 10.13.4, my display brightness resets to about 90 percent (2 bars below maximum) after every restart. I reset PRAM several times and reset SMC, also several times. This had no effect. I used the delta update initially and later the combo updates. The behavior still persists. Other than this weirdness the iMac Pro seems to be working fine.

My other macs (2012 Mac Pro and 2015 MacBook Pro) are not affected by this -- the delta update was applied in both cases.

I went through layers of tech support, only for them to say “it is isolated to certain iMac pro machines and will have to wait for next firmware update. I was so mad. Imagine such an expensive machine with such poor support...the head does not know what the tail is doing. I asked to speak to an engineer and they said that was not possible. So I am unsure if the Mac was replaced if it will resolve the problem if it is a problem for few machines or all. Only those who caliberate the Mac will know.

About the macOS High Sierra 10.13.6 Update - Apple Support

Others are reporting other brightness issues with iMac Pros. Here is the macrumors link:

https://forums.macrumors.com/threads/imac-pro-auto-brightness.2103184/#post-2595 2738

Read all the way to the end. I have not had time to verify the auto-brightness problem referred in one of the posts, but you might try to replicate it and mention it to Apple on Thursday.

Gene

Thanks for the update. I guess I am not too surprised. Hopefully, as more and more iMac Pro owners report this problem, Apple will put more effort into solving it. To me this looks like a firmware issue more than a software one. Per my earlier messages, I restored to 10.13.3, but the brightness issue persisted.

Whatever Apple did with this update, it broke the way the T2 chip handles brightness settings. There are other posts on the MacRumor forums claiming that it's not just brightness retention on startup that's broken, but USB connectivity is also suspect (slow keyboard responsiveness, etc.) until the computer fully loads the OS. You probably noticed, but it's impossible to lower the brightness using the keyboard until the OS fully loads; doing so before the login screen appears does not work. Nor is lowering the brightness possible while in recovery mode.