Less brightness after plugging once my macbook pro to a thunderbolt display 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?
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 feedback@apple.com