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.

Human observers have been demonstrated to be sensitive to the local (physical) light field, or more precisely, to the primary direction, intensity, and diffuseness of the light at a point in a space. In the present study we focused on the question of whether it is possible to reconstruct the global visual light field, based on observers' inferences of the local light properties. Observers adjusted the illumination on a probe in order to visually fit it in three diversely lit scenes. For each scene they made 36 settings on a regular grid. The global structure of the first order properties of the light field could then indeed be reconstructed by interpolation of light vectors coefficients representing the local settings. We demonstrate that the resulting visual light fields (individual and averaged) can be visualized and we show how they can be compared to physical measurements in the same scenes. Our findings suggest that human observers have a robust impression of the light field that is simplified with respect to the physical light field. In particular, the subtle spatial variations of the physical light fields are largely neglected and the visual light fields were more similar to simple diverging fields than to the actual physical light fields.

As LEDs respond almost instantaneously to the driving current, they are susceptible to Temporal Light Artefacts (TLAs). We used the results of more than 10 perception studies to quantify the visibility of these TLAs. The developed and validated visibility measures can be used to design LED light sources with high lighting quality in various applications.

No abstract