An increase in wavelength can affect transmittance readings in different ways depending on the materials involved. For example, in a simple spectrophotometer, an increase in wavelength can cause a decrease in transmittance as the material absorbs more light, particularly if the material has strong absorption bands in the higher wavelengths. However, in other types of materials, particularly those that scatter or reflect light, an increase in wavelength can actually lead to an increase in transmittance as more light is transmitted through the material. In general, the relationship between wavelength and transmittance is complex and depends on a variety of factors including the composition and thickness of the material, the type of radiation used, and the presence of other substances that may interact with the light. It is important to carefully calibrate instruments and account for these factors to ensure accurate transmittance readings.