@Asmyldof "It's very possible the loadcells have some light dependance, but don't forget that when you actively hold a book between the lamp and the circuit, your hands can also work as a sort of EMI-lightningrod. Since your body is a coupled capacitance to the environment. If you want to truly experiment whether it's light dependence you should not move the lamp and build something between it and the circuit with plastic and/or cardboard and remain at the same distance.
Other than that, breadboard circuits with all kinds of wires running around are a very good target for noise. Step one wo…