The impingement on the photoelectric cell of stray light due to internal reflections or diffusion effects shall be reduced to a minimum (e.g. by finishing internal surfaces in matt black and by a suitable general layout).
Delež razpršene svetlobe, ki pade na fotoelektrično celico zaradi notranjih odbojev ali difuzije svetlobe, mora biti kar najmanjši (To se doseže npr. z notranjimi površinami, prebarvanimi v črni mat barvi in z ustrezno razporeditvijo).