I own a MacBook Pro 13". It has 16GB of RAM and it's connected to a 27" Thunderbolt display. I use it for everything. Programming, photography, and even run Windows on it in VMWare Fusion and do most of my Windows programming on it as well. The one problem I have with it (well other than the hard-edge of the chassis which I filed down to save my palms from the constant pain) is that depending on where I am or what the ambient light is, the brightness of my screen needs to change so I can view my screen without strain. Now this wouldn't be a big deal if I didn't go through the trouble of color calibrating my displays with an X-Rite colorimeter. See, I need that for photography. I need a color calibrated display when editing photographs so that when I print, my prints match what I see on my display. If my display is too dark, too light, too blue, too magenta, etc. then my prints will look just as weird.
The problem is that the brightness or luminance of the display directly affects the color calibration of my display. If I change the brightness during the day because I'm at a coffee shop and the lights are bright, when I get back to editing photos, I have to make sure my brightness is at the color calibrated level. With my MBP and Thunderbolt display, the OS keeps track of the brightness level via the System Preferences under Display and all I have is this slider control to use and make my best guess of putting it back where it once was. That's not really acceptable to me. I need it to be more precise. I do the bulk of my printing on an Epson 4900 and the cost of refilling all the inks goes into four digits. I can't afford to have prints that don't match my display because my display isn't calibrated properly.
I could carry around my colorimeter with me everywhere I go and pull it out every time I need to reset my brightness but that's not practical at all. It's not a very long or intensive process but for heck's sake, all I need is to put the brightness level back to where it was when I calibrated the display! There should be an easier way. I searched for one in the Mac app store and couldn't find what I was looking for so instead I decided to write an app myself and solve this little dilemma.
So I made Luminance. It's a little icon that sits in the OSX menu bar on the right-hand side where all the other system-tray-like icons sit. Here I can click on it and know exactly what my brightness level is in percentage of full brightness is for all my active displays. I can save the current brightness level and then later recall it. I can also change the brightness level of any active display. This solves my problem. Now I can change my display brightness at any time without fear of being able to return to the saved and calibrated display brightness level.
Now there is one shortcoming of this app. It only works for displays where the OS controls the brightness level. If you have an external display where the display controls the brightness, this app won't be able to record and change the brightness level. I knew there are lots of artists and photographers which use high-end displays from NEC, Lacie, Eizo, etc. and those displays directly control their brightness level via controls on the display itself. This app won't work for those displays.
I haven't published this app in the Mac app store just yet. I'm not sure its worth the $99 Mac Developer license right now. I also may create a dock icon and dock menu for the app for those times when the OS decides that there's no room in the menu bar for my icon and the OS removes my icon. If its in the dock, you can still access the functionality there. I have about 5k+ people who have circled me on Google+ and I put the word out there about this little app to see if there was any interest in it and to my surprise there was no response really.