This research aims to investigate photocells reactor design can convert indoor lights energy into electrical energy. Indoor lights comes from sunlight entering into the room and fluorescent light irradiation. Design of photocells reactor use a panel of copper oxide (Cu2O/CuO) of calcined Cu plate and filler electrolyte Na2SO4 0.5 N. Modification of electrode by n-p junction layer, which one of section (n) and the others section (p). Photocells reactor was constructed by thickness of the glass pane, the distance between the electrodes, the interface layer, layer and coating reflector panels. In this research there are three design of photocells reactor, The first design is R1, the thickness of the glass panel 3 mm thick reactor 15 mm without anti reflector. In this design, there are two type based on the difference at the junction of type n, (R1a = plate Cu; R1b = plate Aluminum) generate 182.82 mW/m2 and 21119644.3 NW/m2. Than, the second design of photocells reactor is R2a (junction-type n = plate Cu) and R2b (junction-type n = plate Al), a panel thickness of 15 mm and has a layer anti reflector provide power 214.95 mW/m2 and 24163298.3 NW/m2. The last design of photocells reactor is R3 (R3a = Cu) and R3b (Al), thickness of 9 mm, the distance between the electrodes 0.30 mm, using anti reflector carbon, giving each the power of 277.36 mW/m2 and 31258420.91 NW/m2. The most optimum reactor design is R3b with 2:14% conversion capabilities (Intensity = 90.21 foot candles) for indoor lights.