With some types of ion selective electrodes (e.g. mom-crystalline solid membrane electrodes), light may have an impact that causes the electromotive force to chage.
If you will use one of these types, it is not desirable to take measurements in a place exposed to strong light or where the luminous intensity changes.
when using such an electrode, avoid the exposure of the light, for example, by using a brown beaker.
Generally, electrodes with the ion selective membrane whose main component is silver halide, such as Cl-, Br-, I-, CN-, may receive the impact of the light.