Reflectance, transmittance, and temperature of the arterial wall exposed to air are measured during laser irradiation for different heating dynamics. Temperature dependence of the reflectance and transmittance is then deduced. Our results show a competing effect between temperature and dehydration, resulting in a distinct minimum of transmittance and maximum of reflectance. As a consequence, a direct correlation of reflectance and transmittance with temperature is only possible for a specific dynamics.