Lighting that gradually changes over time, also known as dynamic lighting, is an integral part of our experience of illumination. Daylight is a prime example of this, and LED technology has led to its increasing use in artificial lighting as well. However, perception of dynamic lighting has not been extensively studied. Previous work has focused exclusively either on daylight illumination or relatively chromatic illumination, and most research examined lighting transitions at speeds near detection thresholds. Past studies have found that the perception of illumination changes is far from uniform across color space. Perception of transitions has been found to vary depending on whether the change is in the chroma or hue direction, what the base color is, and whether the change is towards or away from a neutral chromaticity. This experiment investigated transitions between neutral and chromatic illumination to expand upon these findings. These stimuli were chosen to best address two questions: does the relationship between hue and perceived speed found previously differ with chroma level, and does the effect of the orientation of the transition relative to neutral apply to stimuli outside of the daylight locus and at speeds above detection thresholds? In this work, the perceived speed of transitions from a neutral illumination to a chromatic one and vice versa in a total of sixteen hue and orientation combinations, including four along the daylight locus, was measured. A two-interval forced choice (2IFC) experiment using the method of constant stimuli was performed, in which observers reported whether the reference or comparison stimulus appeared faster. Stimuli were three second equiluminant transitions, linear in CIELAB, in eight radial hue directions, two orientations relative to neutral, and five speeds in ΔEab*/s increasing logarithmically. The proportion of times the comparison stimulus was judged faster than the reference across all observers was computed, and probit regression was performed to fit psychometric curves to the data. The point along each curve at which the proportion was estimated to be 0.50 was the point of subjective equality (PSE) or threshold for that transition direction, representing the speed in ΔEab*/s at which the transition would be perceived as equal in speed to the reference. The PSEs of transitions moving away from D65 differed for different radial hue directions, indicating that CIELAB is temporally nonuniform. Difference formulas in CIELAB and the coneopponent DKL space were weighted to minimize the standard deviation of the PSEs in order to investigate the nature of a more temporally uniform space. The standard deviation was minimized when very small weights were attached to the Δb* and Δ(S – (L + M)) terms, respectively, indicating that these axes contribute less to speed perception, in line with previous literature. The PSEs of transitions moving towards the neutral D65 chromaticity were incalculable for all but two radial hue directions, as the slowest comparison transitions were still judged faster than the reference in more than 50% of the observations. This result suggests that either the comparison to a reference with a different orientation relative to neutral was too jarring to provide meaningful data, transitions moving towards the chromaticity of D65 have PSEs outside the range of stimuli tested, or both. Overall, the relationship between perceived speed and hue was found to vary from that found in previous experiments at higher chroma levels, but results aligned with past research when considered in the context of color- and cone-opponent axes. The relationship between perceived speed and orientation relative to neutral requires further study.

Library of Congress Subject Headings

Motion perception (Vision); Lighting--Special effects; Color vision

Publication Date


Document Type


Student Type


Degree Name

Color Science (MS)

Department, Program, or Center

Color Science


College of Science


Michael J. Murdoch

Advisor/Committee Member

Susan Farnand


RIT – Main Campus

Plan Codes