Using Flickering Light to Enhance Nonimage-Forming Visual Stimulation in Humans

Area of Science:

• Ophthalmology
• Neuroscience
• Photobiology

Background:

• Intrinsically photosensitive retinal ganglion cells (ipRGCs) regulate non-image-forming visual functions.
• Optimizing light exposure for ipRGCs offers potential health benefits, including improved circadian rhythms and mood.
• Flickering light may offer a more effective method for stimulating ipRGCs than continuous light.

Purpose of the Study:

• To investigate the efficacy of flickering light in enhancing ipRGC excitation.
• To determine the optimal flicker frequency and duty cycle for maximal pupillary constriction.
• To compare the effects of flickering light versus steady light on pupillary responses.

Main Methods:

• Human subjects were exposed to a matrix of 463-nm flickering light stimuli.
• Varied parameters included photon counts, duty cycles (12%, 47%, 93%), and flicker frequencies (0.1-7 Hz).
• Steady-state pupillary constriction was measured to quantify ipRGC response.

Main Results:

• A 2 Hz flicker with a 12% duty cycle at 13.7 log photons cm⁻² yielded the greatest pupil constriction (48% ± 4%), 71% higher than continuous light.
• Similar optimal flicker parameters (2 Hz, 12% duty cycle) were found for 14.7 log photons cm⁻² stimuli, showing a 38% increase over continuous light.
• For the highest intensity (15.7 log photons cm⁻²), 1 Hz with 47% duty cycle was optimal, achieving similar constriction levels.

Conclusions:

• Pupillary constriction is significantly influenced by flicker frequency and duty cycle, in addition to light intensity.
• The optimal stimulus for maximal pupillary response was 13.3 log photons cm⁻² s⁻¹ flickering at 2 Hz with a 12% duty cycle.
• Findings can guide the development of healthier architectural lighting and improved phototherapy for circadian rhythm disorders and seasonal affective disorder.