Fig. 1

White light photos of the system (a) and the boards of LEDs, amplifier and Uno controller (b); schematic diagrams of the system (c) and boards (d); a LED spatial distribution diagram and numbers (their X and Y distance coordinates are in Table 2) (e); circuits for controlling LEDs via the Uno R3 board (f) and the inverting amplifier for the temperature signal (g); a schematic diagram for measuring sample absorption coefficient using a microcuvette.