Real-time calculation of reflectance requires the use of a diffuse reflectance standard during measurement of incident illumination, which is also known as the 'white reference' or 'baseline'. Typically reflectance is used for solids, although it can be used with liquids under the right viewing geometry. The white reference can be measured with the instrument viewing the incident illumination, that passes through a nearly transparent lambertian diffuser, or is collected by an integrating sphere, or that is reflected off of a nearly 100% reflective lambertian panel. The most convenient and most common approach is to use a reflective panel. Aim the fiber optic at the panel then click on the OPT button to adjust the instrument gain for optimal performance. Dark offsets are also determined and stored for automatic subtraction from reflectance calculations.

After the optimization process is complete, click on the WR (white reference) button to save a reference spectrum to be used in the reflectance calculation. Be sure to keep the fiber optic cable pointed at the reference panel during this operation.

A good white reference material is Spectralon^® which is a registered trademark of Labsphere, Inc.