The Influence of Speed and Amplitude on Visibility and Perceived Subtlety of Dynamic Light

Abstract

LED lighting can provide pleasant temporal dynamics, though the understanding of what constitutes pleasant has so far remained largely in the experiential domain of lighting designers. Only recently has research begun to uncover what affects preferences for dynamic lighting. Based on the insight that visible, yet subtle, dynamic lighting is desirable, an experiment was conducted which studied the influence of the speed and amplitude of periodic temporal color transitions on the thresholds for visibility and perceived subtlety. Using RGB LED lights to illuminate a wall in a living room setting, stimuli with periodic color transitions were presented to 40 observers, half of whom evaluated whether the dynamic transitions were visible, and half of whom evaluated whether the dynamics were subtle. The observers' data were fit using psychometric surfaces over the independent variables speed and amplitude of transitions. The 2D contours at the middle of the height of these surfaces were taken as thresholds. Experimental confidence was estimated via parametric bootstrapping, showing significant effects of the location and direction in color space in which the transitions were made, further strengthening the need for a temporal difference based color space. Interestingly, a distinct difference between the threshold for visibility and the threshold for subtlety can be seen, allowing for the creation of transitions that are both visibly and yet subtly dynamic. The results indicated that observers are more sensitive to hue changes than to chroma changes, and observers are more sensitive to hue changes in the orange region than to those in the blue region. Additionally, questionnaire responses provided insight into interpretations of the word subtle, understood to be pleasant, gentle, and smooth, which are also terms used to describe desired characteristics of dynamic lighting.