Help - iMac 5k won't get fully bright

[MacMyBitchUp]

I've just bought a late 2015 iMac 5k (used, sadly!), and there seems to be a problem with the brightness. I noticed fairly quickly that the screen isn't as bright as either my Macbook Air or the Thunderbolt display I was using previously. The brightness control only makes any difference for the first five "blocks", after that any increase makes no difference. I am running 10.13.3. Here are all the things I've tried so far:

Turning off auto-brightness (makes no difference). Night Shift is also off.
Resetting the PRAM
Resetting the SMC
Turning it off and on again!
Running diagnostics (no issues found).

Nothing has made any difference.

The screen is equally bright across all of it - no dark corners / sides.

Can anyone help me work out what's going on?!

 

[Glockworkorange]

I recall reading somewhere (and take this with a grain of salt, because i cannot remember where for the life of me) the screen brightness can be limited by the ambient lighting of your surroundings.

I just dd a Google search and couldn't find anything, so maybe I dreamt it

 

[MacMyBitchUp]

I recall reading somewhere (and take this with a grain of salt, because i cannot remember where for the life of me) the screen brightness can be limited by the ambient lighting of your surroundings.

I just dd a Google search and couldn't find anything, so maybe I dreamt it

It's not that - as I say I turned that feature off. Other stuff I've tried:

- hooking up the thunderbolt display - mac controls display brightness no problem, and it's much brighter than the iMac display

- downgrading to 10.11.6 - same issue.

:-(

 

[Glockworkorange]

I

It's not that - as I say I turned that feature off. Other stuff I've tried:

- hooking up the thunderbolt display - mac controls display brightness no problem, and it's much brighter than the iMac display

- downgrading to 10.11.6 - same issue.

:-(

I'm not referring to auto brightness. I don't think there is a feature to turn what I am referring to on or off.

You can't get the machine to 500 nits (at least that's what mine is) unless the ambient lighting is a certain way.

 

[chscag]

Just a guess here.... you may have a failing or weakened backlight. Your iMac uses LEDs for backlighting and that's the circuitry you probably need to focus on checking. You can try going to www.ifixit.com and see if there are similiar problems with screen brightness as yours. They (ifixit) may have some troubleshooting steps you can follow.

I have a 2017 27" iMac and the screen is always too bright for me, so bright that I have the control turned down almost to the lower ⅓ of fullness. I'm not sure that ambient lighting makes much of difference with the newer retina screens since I'm not the only one who has noticed this. The brightness spec of 500 nits is very subjective. I have older eyes so that may be a factor.