I believe this will answer your question, this is from an article from DisplayMate. DisplayMate is a company that test screens from HD tv, cellphone screens and so on. I do not believe a lot of people may know this when you use your Note 3 outside in direct sunlight you have to use auto brightness on your note 3. The reason for this normal use the screen is about 400 nit however when using auto brightness in direct sunlight the screen goes from 400 nit to 660 nit which is impressive here is the article..
Impressive Brightness
Up until the Galaxy Note 3, OLED displays have been somewhat to significantly dimmer than competing LCD displays. The Note 3 has changed that in a big way…it’s an impressive 55 percent brighter than the Note II and a solid 25 percent brighter than the Galaxy S4. For most image content it provides over 400 cd/m2, comparable or higher than most LCD displays in this size class. Even more impressive is that when Automatic Brightness is turned on, the Note 3 hits an incredible 660 cd/m2 in high ambient light, where it’s needed (85 percent brighter than the Note II and 40 percent brighter than the Galaxy S4 with Automatic Brightness) – the brightest mobile display we have ever tested in the Shoot-Out series. An impressive achievement for OLEDs!
Galaxy Note 3 Display Technology Shoot-Out
Note that Auto Brightness mode can set the brightness higher than you can with the brightness slider.