Which statement regarding reflectometry is considered true?

Reflectometry is a technique that measures the reflectance of light off a sample to determine the concentration of specific substances. The statement regarding the use of an opaque film as a white reference to set 100% reflectance is accurate.

In reflectometry, 100% reflectance is a standard reference point that ensures measurements are relative to an ideal state where no light is absorbed or scattered by the sample. This opaque film, often referred to as a white reference, provides a consistent baseline for comparison, enabling precise quantification of the reflectance of the test sample.

The other statements may lack completeness or accuracy regarding the method's application. For instance, while there can be scenarios where a non-linear relationship is observed between reflectance and concentration, single-point calibration is not commonly sufficient for establishing concentration across a range of values. Similarly, while diode arrays can be used for many optical applications, the standard for reflectometry often involves different types of detectors optimized for light measurement. Thus, the reference point provided by the opaque film is essential for the reliable execution of reflective measurements and serves as a foundational aspect of the technique.