I own a Macbook pro (15'4) with Yosemite.

I used to use it without an external display. The brightness was very powerful :)

I've just plugged a thunderbolt display (Mac 27''), and then removed it. I even restarted my MacBook pro right after.

Now, I found that the brightness is not as powerful as before, even on MAX :(

My color profile is the one by default (LCD color).

Is there an explanation? Have someone ever experienced this?

  • 1
    You could try to fix this with a PRAM reset on startup (hold cmd+alt+p+r) until your mac restarts. (support.apple.com/kb/PH18761)
    – Jules
    Aug 23, 2015 at 11:38
  • !! It works... Is it a REAL bug with apple 27 display ?
    – Mik378
    Aug 23, 2015 at 11:43
  • Not that i know of, give me a few minutes to explain in an answer ;)
    – Jules
    Aug 23, 2015 at 11:47
  • Also, have a look here: apple.com/feedback
    – Jules
    Aug 23, 2015 at 13:11

1 Answer 1


You could try a NVRAM reset by starting your mac and holding the following keys:

CMD + ALT + R + P.

(More info)

When your Mac restarts, you could release the keys.

Some say that you have to do this 3 times for the best result, but I can't explain why

More information about a PRAM/NVRAM reset can be found on the Apple Support Website

When you use your Mac and connect it to displays or change the screen's brightness, it could be that your settings become a bit corrupted. You could erase those settings by preforming a PRAM reset as explained above.

I can't find any known bugs on the Apple Diagnostics website, you could report it by sending a mail to [email protected]


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