If you are struggling with the concept of how Brightness and Luminosity affect colour check out the video above.
My good friend Conny Walstrom talks about the differences between Brightness and Luminosity within Photoshop.
He covers a few modules of how Photoshop Handles colour inside HSB (Hue, Saturation, Brightness), HSV (Hue, Saturation, Vibrance), HSL (Hue, Saturation, Luminosity), Grayscale, Luminosity and Perceived Brightness.