The instrument, designed for measuring the diffuse transmittance, is equipped with an integrating sphere under the diffuse illumination system and it provides precise and stable measurement values, especially in the transmittance measurement for the light diffusible objects and specimen which are being transparent, translucent or with concavo-convex, and even lens. The double-beam mechanism can offer a long stability of the instrument performances, and a specimen table, being designed upward allows easy to set samples. Since a thick sample (max 30mm) is acceptable, DOT-3C is particularly ideal for the measurement of the transmitted color for the lens of spectacles.