How is refractive index different from absorbance which is conventionally measured with a spectrophotometer?

The spectrophotometer can measure the attenuation (absorbance or optical density) at a wavelength or as the full spectrum is scanned. Absorbance or optical density is relevant when substances are colored or absorbing light. The refractive index is a physical property of a substance at a specific wavelength. Our online software calculates the refractive index internally at 589 nm.