When light enters an air wedge formed by two glass plates, the wavelength remains that of air because the interference patterns are generated in the air gap, not in the glass. The glass plates serve primarily as a means to visualize the experiment, while the actual interference occurs in the air. If the medium changes, such as when water is introduced, the wavelength would then need to be adjusted accordingly. The path difference for the interference is determined by the thickness of the air wedge, which remains constant regardless of the glass. Thus, the wavelength conversion is only necessary when the light interacts with a different medium, like water.
