Effect of Rear Lamp Shape and PWM Frequency on the Visibility of the Phantom Array Effect

Light Emitting Diodes (LEDs) have become the primary light source in automotive lighting, with widespread adoption in rear lamps of modern vehicles. Pulse-Width Modulation (PWM) is commonly used to control LED brightness, but it can introduce temporal light artefacts such as the phantom array effect, which may cause visual discomfort or distraction to drivers. Although previous research has examined the effects of flicker frequency and eye movement on this phenomenon, the influence of the physical design of the light source—particularly in actual automotive rear lamps—has not been thoroughly explored. This study examines how the shape of rear lamps (horizontal vs. vertical configurations) affects the visibility of the phantom array effect. Using two production car lamps—a horizontally elongated lamp and a vertically elongated lamp—we measured the threshold frequencies at which the phantom array effect became perceptible and collected subjective visibility ratings. The results suggest that rear lamp geometry can affect the perceptibility of the phantom array effect. These findings may provide useful guidance for rear lamp design aimed at reducing visual artefacts and improving driver visual comfort.