Photocatalysis has been studied and considered a green and effective approach in addressing environmental pollution . Photocatalysis has attracted for its versatility in the environment and energy sector. In the environmental field, photocatalysts can be used to remove pollutants in the air and water. The photocatalytic process can eliminate the total toxicity with products of CO2, water, and other fewer substances . In the energy field, photocatalysts can generate alternative fuels such as H2, O2, and bioethanol via water splitting or reducing CO2 . In the photocatalytic process, photocatalysts are activated by a suitable light source to induce photocatalytic reactions. The use of light gives photocatalytic technology a great advantage compared to other waste treatment methods such as adsorption or filtration. However, the catalysts' optical and electrical properties and photocatalytic mechanisms are not paid needed attention to compared to the sole efficiency future photocatalytic application. This work highlights key techniques to study optical and electrical properties in reporting photocatalysis. In addition, the current mistakes and inconsistencies in interpreting these properties are presented and revised. Here, TiO2, g-C3N4, and SnO2 are used as representatives because TiO2 is the most studied photocatalyst (accounting for 52.5% of studies in this field, Web of Science, March 2021), g-C3N4 is an emerging nonmetallic photocatalyst (7.8%), and SnO2 is an emerging photocatalyst (1.6%). The bandgap of TiO2, SnO2, g-C3N4 is determined by diffuse reflectance spectroscopy (DRS), choosing the compatible light source becomes more straightforward. The conduction band (CB) positions and the valence band (VB), which determine the redox abilities, are obtained by the Mott-Schottky technique. The supporting states in the bandgap of the materials are investigated by Photoluminescence (PL). The band structure of their composites is studied by X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS). The understanding of optical and electrical features of photocatalysts not only supports research expansion into new materials/composites and but also enables researchers to design wastewater or air pollution treatment systems with the suitable operation time, area, light source, and conditions, which helps to optimize the photocatalytic activity of photocatalysts and systems.