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Design details of the smartphone-LED prototype device (a) and its outlook with a smartphone on it (b): 1—smartphone, 2—sticky fixing platform with a camera window, 3—holding ring, 4—polarizer of the detected light, 5—LED ring comprising four sets of LEDs, 6—light diffuser, 7—illumination polarizer (oriented orthogonally to the polarizer 4), 8—screening spacer, 9—silicone skin contact ring, 10—compartment for batteries and electronic components [17].
