Fig. 5.
RRS response of various carotenoid solutions under 488-nm excitation, shown as a function of increasing concentrations—filled triangle, β-carotene; open triangle, zeaxanthin; open square, lutein; and open circle, lycopene. The response is linear up to ~5 μg/mL, which is a carotenoid concentration exceeding that found in human skin. Slight variations in the slopes for each carotenoid solution are in very good agreement with their respective excitation efficiencies. Note the near coincidence of responses for lutein and zeaxanthin.