The multilayer system was TiO2 film deposited on industrial ITO substrates. How can we measure weighted reflectance from reflectance measurement?
There are few reasons for red shift of T: 1) If your TiO2 film is rough than the scattering losses increase resulting in smaller transmittance; 2) If TiO2 is thick enough a small extinction coefficient in the visible range may lead to absorption that is not negligible; 3) If both materials are smooth and transparent than it may happen reflectance of TiO2/ITO to be higher than R of ITO.
The optical band gap of TiO2 (3.0 eV for anatase, or 3.2 for rutile) is less than that of ITO (about 3.7 eV).
Response to question 1: The redshift could be a simple interference effect. What are the thicknesses? (particularly for TiO2)
Response to question 2: Assuming that you mean the 'luminous reflectance', then it would be the integration of reflectance*photopic_curve*source_spectrum, divided by the integration of photopic_curve*source_spectrum. You can find the photopic curve easily; for the the source_spectrum, you can use a 'perfect' source of unity, or a standard like D65.
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