Effects of Temporally Modulated Illumination to Human Beings: Nine Statements from a Research Perspective
Light sources, which are temporally modulated in emitted radiation, may induce several direct perceivably artefacts to human beings, for instance, visual unsteadiness in intensity or spectrum of light (flicker effect), in motion (stroboscopic effect) or in perceived shape or spatial position of objects (phantom array effect). Several experiments with LED light sources have been conducted recently, within which visibility thresholds for flicker and stroboscopic effects were derived.
Studies over the past 60 years have clearly shown that three factors (related to the luminaire, subject and environment) mainly contribute to the occurrence of visible as well as non- visible effects of temporally modulated lights. Today there is evidence, that the amount, frequency and modulation depth of the emitted light, the size of the light emitting surface, the spatial position of the luminaire within the field of view, the age and arousal level of the exposed subject, and fast moving objects (e.g., at industrial workplaces, in sports, on roadways), fast eye movements (e.g., during proof-reading) or fast head movements play a crucial role.
Published methods and metrics and design recommen- dations from the International Commission on Illumination and the German Electrical & Electronic Industry take perceivable effects of temporally modulated illumination of up to 2000 Hz after short exposure into account. However, distinct detrimental effects on human beings have been derived from imperceptible light modulation during extended exposure to either fluorescent lamps or CRT display light.
In the following, human impact research on temporally modulated lights is critically summarized in nine statements. Furthermore, core limitations of studies with different LED control strategies are described and topics for future investiga- tions are outlined.