Electric light sources could produce light flickers that might have biological effects. Although light flicker is not always visible to the human eye, it may impact certain human health. Eye strain, headaches, migraines, impaired vision, and, in sensitive people, photo epilepsy are just a few of the negative impacts of light flicker. Many international organisations have been working on lighting standards measurement in response to the growing concern about the flicker rate. This paper's aim is, besides summarising data from the literature, to give measured data for the flicker rate of some light sources available in Serbia and suggest further steps in the light designing process regarding flicker to avoid adverse biological effects.