There's more...

It is important to note that the way the brightness levels are implemented means that you can only change all the NeoPixels at one time. That is, with the brightness property, you cannot make some pixels brighter and some pixels darker. So, whatever value you set for brightness will apply to all the pixels on the board.

The pixels have the capability of being very bright when they are left at the maximum level of 100% brightness. An example of where this setting is more suitable is when you embed your device in a plastic container. The following photograph is taken from a NeoPixel project, where the Circuit Playground Express board was placed inside the base of a snow globe:

In this project, the base is made of white plastic. So, even though the board is not directly visible, the pixels are bright enough to shine through the white plastic and fill the whole globe with light.