Barnes & Noble NOOK Tablet User Manual page 48

The picture below shows the Text controls available for books.
Adjusting the Brightness of the Screen
It's easy to adjust the brightness of the screen while you're reading a book. Just do this:
1. Tap the center of the page to make the Reading Tools appear.
2. Tap the brightness icon.
Your NOOK displays a brightness control that features a slider for dimming or brightening the screen.
3. Use the slider to adjust the brightness of the screen.
Move the slider to the left to dim the screen. Move the slider to the right to brighten the screen.
4. When you have adjusted the brightness to your liking, tap the center of the page again to make the brightness
controls and the Reading Tools disappear.
48
The text control tools.
Barnes & Noble NOOK Tablet User Guide