21 ½ iMac screen suddenly goes dim

[Jonzjob]

My old late 2009 iMac 21 ½ sunning High Sierra 10.13.6 has had the screen go dim suddenly. It has only happened twice in the past few weeks. When I checked the screen brightness I found that it showed completely dim and could be restored simply by using the brilliance keys on the keyboard, F1 & F2.

I had wondered if it had gone into Night Shift mode when I did a search on 'screen going dim', something we have never used, and as I couldn't find how to check I pressed Command/Space and asked Siri for 'Night Shift'. A Sys Pref window came up titled 'iMac' which is something else I've never seen before and when I brought up the Sys Pref window I couldn't see it on there?

The Boss, wife, was using it both times when it dimmed down. Not doing anything in particular and she said that when she tried opening System Preferences using either the the Apple logo top left of screen or the Sys Pref icon in the Dock all she got was the . She put the machine to sleep and when I woke it that was when I found the brightness in full dim.

Any ideas please folks? I have to admit to being really idle as this old machine should have been migrated to our new one and shut down months ago!

 

[MacInWin]

The Boss must be somehow pressing a combination of keys to lower the brightness. It's been a long time since I ran HS, but on my current MBP the CMD/space produces an input window for Spotlight search and searching for "Night Shift" reveals nothing. Nevertheless, I think you may want to look at System Prefs and Displays, then see if "Night Shift" is in the bottom right corner of the box. That's where it is for me. But Night Shift changes the tint, not the brightness, at least for me,, so that may not be what you are looking for. I'm still betting on an accidental key combo, and would look at SysPref/Keyboard/Shortcuts to see if something here is programmed to dim the screen.

 

[pm-r]

My old late 2009 iMac 21 ½ sunning High Sierra 10.13.6 has had the screen go dim suddenly.

Maybe check out this list of things to check:

How to Keep the Screen From Dimming on a Mac

There are two primary reasons for your Mac's screen to dim, and both are easily controlled. No matter which Mac model you have, the power settings may dim your screen after a few minutes if you do not touch the keyboard or the mouse. This is a warning that the display will soon go to sleep, so...

smallbusiness.chron.com

- Patrick
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[Jonzjob]

I had checked the Display in SyS Pref Jake but no Night Shift there



As far as I know Patrick on one of the occasions she was just reading something on a web page? So no key input.

I am a bit incapacitated at the moment after a dammed great abscess appeared smack in the middle of my back and had to be drained. So that I haven't been able to much running aroung for the past few weeks, so I may be able to get this thing wrapped up and the iMac got rid of? That would cure the problem, at least for us

 

[ferrarr]

I don't think that iMac will run Night Shift.

Use Night Shift on your Mac - Apple Support

Night Shift automatically shifts the colors of your display to the warmer end of the color spectrum after dark.

support.apple.com

 

[pm-r]

As far as I know Patrick on one of the occasions she was just reading something on a web page? So no key input.

No Doubt it was one of the cats... No question... Even if it was a neighbor's cat... ;-)

Always blame the cats... One of the first rules... And usually one of the first causes... ;-)

My 2011 iMac has a System Preference option somewhere that tells the screen to dim just before it goes to sleep... I guess as some sort of warning...
But it does make the process a little bit more gradual than just suddenly going totally black.

Maybe you just happened to catch it at that particular moment if you have such a setting set???



- Patrick
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[IWT]

I don't think that iMac will run Night Shift.

I have an oldish iMac running macOS High Sierra (10.13.6) for reasons related to specific apps.

In System Preferences > Display, Night Shift is shown on the top as in this screenshot I copied from Hi Sierra via Dropbox to my working Mac (Monterey).



Ian

 

[IWT]

What Jon shows in his screenshot doesn't tie in with 10.13.6.

Ian

 

[MacInWin]

I think Night Shift is a red herring. It doesn't dim the screen, it changes the tint to reddish. I wonder if The Boss, in reading/watching whatever it was, let the system time out by not touching a key, moving the mouse, or touching the trackpad (assuming one of those, of course)? So, look at Sys Prefs/Power, I think it was called, and see how long it is set before the screen goes dark.

 

[Jonzjob]

Can't blame the cats as I have a catapult and did you know that if you bounce a stone about a foot away from a cats nose it can accelerate from nought to sixty in about 1/4 of a second.

It does dim just before sleep, but then don't we all, but this doesn't come back to bright when you hit a key.

I agree Ferrarr and the first time I saw Night Shift was when we got the new iMac.

 

[pm-r]

What Jon shows in his screenshot doesn't tie in with 10.13.6.

Ian

The screenshot that he posted in his #4 post looks pretty well identical to what my 2011 27in iMac running Mavericks 10.9.5 shows:




- Patrick
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[IWT]

Exactly, Patrick.

Different in Hi Sierra (10.13.6)

Ian

 

[pm-r]

It does dim just before sleep, but then don't we all, but this doesn't come back to bright when you hit a key.

Does it come back to normal brightness when you hit any key if it has gone completely dark as set in Energy Saver preferences pane???

Or does it suffer from the not waking from Display sleep syndrome???




- Patrick
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[pm-r]

Different in Hi Sierra (10.13.6)

I cannot confirm that as I got rid of my High Sierra partition a while back.



- Patrick
=======

 

[Jonzjob]

It doesn't come back to normal brightness until the F2 key is pressed several times and before that is pressed the little sunshine window shows no bars. I have tried to do a screen capture of it but it won't do it.

As for the OS and the Display windows. This is a single screen capture.

 

[Rod]

I notice there is no Automatically Adjust Brightness option in the above preferences pane. I had thought that might be responsible, if something covered the camera lens for example. I thought all iMacs had that option?

 

[IWT]

@Jonzjob ,

Jon, I think the reason my Hi Sierra display options and your Hi Sierra ones are different is because I have a Built-in Retina Display and you appear not to. And my old iMac is 27"; yours 21.5".

We both have 10.13.6, but the display options would, I assume, be more advanced with the Retina display??

Ian

 

[Jonzjob]

Rod, both times it has happened the bar graph for the brightness has been hard over to the left.

Ian, we couldn't afford a posh one like yours . Plus ours is a couple of years older. Really, as it's 13 years old I don't think that we can complain toooo much. I couldn't imagine many other manufactures machines lasting that long?

 

[ferrarr]

What Jon shows in his screenshot doesn't tie in with 10.13.6.

Ian

Jons' iMac is older...

 

[IWT]

Jons' iMac is older...

I entirely agree Bob; but there are other factors - post #17. Retina v non-retina. 21.5" v 27". Granted age is intertwined with these.

Ian