You may want to check your sprites for the material, that they are using. Usually, if you create new sprites, they get an unlit material (they will not react to lights, they act as an emissive material, glowing in the dark) as a default material.
However, you can change that to one of the other materials, that come with Paper2D. Try switching it f.e. MaskedLitSpriteMaterialEmissive. This one reacts to lightsources, and will be black, if you use no lights in your scene, but it also comes with an emissive parameter to lighten up your sprite to let it become visible, as intense, as you want.
With the emissive parameter you can make it, that they are barely visible in complete dark rooms, where no light is (f.e. with emissive set to something like 0.1 or 0.2) while they also will react to brighter lighs and lighten up more.
