The Matter Settings section offers some generic options for all the materials, lights and spectrums in your project : 

• The Materials/Double Sided option defines whether materials should be applied on both sides of a surface or only on the face pointed by the normal : see the Geometries section for more details,

• The Area Lights/Emit on both sides option defines whether area lights emit from both sides of the geometry or only in the direction defined by the Unity light,

• The Area Lights/Default Material option defines which material is used on area lights defined without a "Mesh Renderer" component,

• The Spectrums/Preview Illuminant option defines which illuminant is used for the preview color of materials' spectrums : see the Spectrums section for more details on spectrums,

• The Spectrums/Range include Ultra Violet|Infra Red options defines the range in which spectrums can be defined. By default, spectrum ranges are clamped inside the visible wavelength range [380nm;780nm], you can extend this range to [100nm;5000nm], all spectrums in the project will be defined on the selected range. See the Spectrums section for more details on spectrums.