To change the brightness of a layer, use Brightness which you can find in the layer's Adjust settings. When you select Brightness you can use the slider to make the layer lighter or darker. For detailed instructions, see Adjust the visual properties of a layer.
For example, in image 1 above, the pink background has high brightness and is light. In image 2, the brightness is low, creating a dark pink background. Note that the brightness only affects the layer it is set on.