Małgorzata Perz

Modeling the visibility of the stroboscopic effect occurring in temporally modulated light systems

Three perception experiments were conducted to develop a measure for predicting the visibility of the stroboscopic effect occurring in temporally modulated light systems. In the first experiment, different methodologies were evaluated for their measurement error. In the second experiment, the visibilities of the stroboscopic effect for square wave and sine wave light modulations were measured and the results were found to be consistent with previous findings for flicker perception. In the third experiment, specifically crafted, complex waveforms were used to test the theory of frequency summation. Based on the results of these three experiments, a new measure for the visibility of the stroboscopic effect was developed, consisting of a summation of the energy in all frequency components, normalized for human sensitivity.

Quantifying the Visibility of Periodic Flicker

ABSTRACT Three experiments that measure the visibility of periodic flicker are presented. Temporal light modulations were presented to a large visual field to make the results valid for general lighting applications. In addition, the experiments were designed to control for flicker adaptation. In the first experiment, the sensitivity of human observers to light modulations with a sinusoidal waveform at several temporal frequencies up to 80 Hz was measured. The results showed that the sensitivity to flicker (that is, the inverse of the Michelson contrast) is as high as 500 for frequencies between 10 and 20 Hz, which is more than twice the maximum sensitivity reported in the literature. In the second experiment, the sensitivity to flicker for light modulations with complex waveforms, composed of two or three frequency components, was measured. Sensitivity to flicker was found to be higher than the sum of the sensitivities of the individual frequency components of the complex waveform. Based on these results, we defined the flicker visibility measure (FVM), predicting flicker visibility by a weighted summation of the relative energy of the frequency components of the waveform. In the third experiment, sensitivity to realistic waveforms (that is, waveforms of light emitting diode [LED] light sources available on the market) was measured. The flicker predictions of FVM showed a high correlation with the experimental data, in contrast to some other existing flicker measures, including flicker index and percent flicker, demonstrating the usefulness of the measure to objectively assess the visibility of periodic flicker for lighting applications.

Changing color over time

The revolution in lighting we are experiencing goes beyond the basic capabilities of the light sources used and has enabled new ways of improving the overall experience of both lighting and displays. However, specifics of LEDs, the technical driving force behind the revolution, also introduce new challenges. One of those challenges is the temporal control of full-color light systems. In this work we explore the properties of human color vision relevant to the generation of pleasant dynamic light effects. We show that the spatial models of color are unsuitable for predicting temporal phenomena and give steps towards building a new, temporal model.