Phantom array and stroboscopic effect visibility under combinations of TLM parameters

Solid-state light sources can be more prone to larger temporal light modulation (TLM) than conventional sources. TLM visibility depends on wave shape, frequency, modulation depth and duty cycle, and is affected by the sensitivity of the observer. TLM can be visible well above the critical flicker fusion frequency, when there is relative movement between the observer’s eyes and light source, lighted space or moving objects in the field of view. This human subjects experiment explored visibility of the stroboscopic effect (SE) versus the phantom array effect (PAE) with targeted tasks under 74 TLM waveforms. The results showed the SE visibility peaks between 90 Hz and 120 Hz, while the PAE visibility peaks between 500 Hz and 1000 Hz. The phantom array is visible to sensitive participants at 6000 Hz. Both effects are more visible under rectangular versus sinusoidal TLM, higher modulation, and when duty cycles are 10% or 30% versus 50%. Higher sensitivity participants, differentiated using the Leiden Visual Sensitivity Scale, rated TLM waveforms as more visible, especially those inherently harder to see. This work lays a foundation for a PAE metric and guides driver and dimmer designers toward electronic circuits that minimize the visibility of TLM in LED products.