Effect of Different Color Lights on the Internal Clock and Alertness in Humans

Study Overview
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Brief Summary
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The main aim of this study is to investigate the effects of cone-modulated light emitted from a visual display on human circadian physiology and cognitive performance in the evening.

Detailed Description
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The investigators will generate single/multiple cone-isolating contrasts with equivalent stimuli for other cones and melanopsin photoreceptors. The investigators will assess melatonin suppression under three different light scenarios generated using the method of silent substitution by tuning the spectral composition of the light primaries (e.g. LEDs) such that a single target photoreceptor class is maximally stimulated compared to an equal stimulation of the remaining photoreceptors. Additionally, The investigators will examine pupil response, subjective sleepiness, psychomotor vigilance, visual comfort, and skin temperature under three different light scenarios. This allows for new insights into the lights' cone-contribution mechanism to neuroendocrine physiology in the human retina.

Official Title
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Mechanisms of Cone Photoreceptors Contribution on Human Neuroendocrine Physiology and Pupillary Light Responses

Conditions
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Light Flashing

Intervention / Treatment
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* Other: Flickering light stimuli
* Other: Constant light stimuli
* Other: Dim light


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age: 18 - 35 years Sex: male or female normal color vision, male dichromat (i.e. tested by CCT, HRR, Farnsworth Munsell 100 Hue Test) BMI: 18.5 - 29.9 self-reported weight and height (i.e. normal and overweight according to WHO) Signed consent form of participants Chronotype: Morningness-Eveningness Questionnaire (31 - 69) Sleep Quality: Pittsburgh Sleep Quality Index, PSQI (≤5) Exclusion Criteria: High myopia (> -6 diopters) High hyperopia (< +6 diopters) Transmeridian travel (>2 time zones) <1 month prior to the first session of the study Shift work <3 months prior to the beginning of the study Ophthalmological or optometric conditions (cataract, glaucoma, retinal detachment, macular conditions, chronic inflammations, eye injuries, or operations) General health concerns or disorders, including heart and cardiovascular, neurological, nephrological, endocrinological, and psychiatric conditions Medication impacting on visual, neuroendocrine, sleep, and circadian physiology For females only: pregnancy, use of hormonal contraceptives, lactation or breastfeeding Drug (urinary drug screening) and alcohol use Non-compliance with sleep-wake times: >1 deviation from ±30 minute window sleep and wake-up time Extreme chronotype (Munich Chronotype Questionnaire <2 or >7) Current participation in other clinical trials Exclusion criteria due to study requirements: Inability to understand and/or follow study materials or procedures Insufficient knowledge of project language

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Placebo Comparator: Control<br>Dim light condition as a baseline | Other: Dim light<br>* This light condition is the baseline (≤10 lux).<br>|
| Active Comparator: Modulation<br>Flickering light will be added sinusoidally onto the background light. | Other: Flickering light stimuli<br>* The intervention will be exposed to flickering lights (≤200 lux). More specifically, the participants will be asked to be exposed to a specified flickering light (1Hz, 30 seconds On, and 30 seconds OFF) for 2 hours starting at their habitual bedtime (HBT).<br>|
| Sham Comparator: Background<br>Constant light with maximum half irradiance (50%) of all primaries. | Other: Constant light stimuli<br>* The intervention will be exposed to constant background lights (≤200 lux). The participants will be asked to be exposed to a specified constant light for 2 hours starting at their habitual bedtime (HBT).<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Melatonin concentration | The saliva samples will be collected from participants every 30 min. The investigators hypothesize that the cone flickering light stimuli will have a different melatonin-attenuating effect than the constant background stimuli and that both will have a different effect than baseline. | 1 year | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Vigilance performance | Sustained attention performance will be assessed throughout the study, using an auditory psychomotor vigilance test (PVT) approach. The investigators hypothesize that the flickering light stimuli will produce different reaction times as measured with the PVT than constant light and baseline. Besides, the baseline will not yield the same reaction times as constant background light. | 1 year | 
| Subjective sleepiness | The investigators will collect subjective sleepiness ratings using the one-question 9-point Karolinska Sleepiness Scale. The investigators hypothesize that sleepiness (ratings) will be different in the flickering light stimuli than in the constant background light and both will be different than baseline. | 1 year | 
| Visual comfort | To assess each participant's subjective perception of visual comfort, The investigators will use a custom 7-point rating scale that probes brightness, light color, and glare perception based on a selection of questions. The investigators hypothesize that visual discomfort ratings will change in the flickering light stimuli in comparison to the constant background stimuli and baseline. | 1 year | 
| Skin temperature | The investigators will monitor skin temperatures using six surface temperature thermocouples (BS 1922L Thermochron iButton®, Maxim, US) placed on proximal and distal regions of the body surface. The investigators hypothesize that the temperature of the body skin will be different in the flickering light stimuli than in the constant stimuli and both will have a different effect in comparison to the baseline. | 1 year | 
| Pupil response | The investigators will measure changes in the pupil area using a silent substitution Pupillograph. The investigators hypothesize that the pupil constriction will be different after exposure to the light conditions as cones and post-receptoral channels adapt to the light stimuli. Besides, the pupil constriction will change differently under the cone-modulated light when the direction of stimuli is identical to the direction of flickering light condition. | 1 year | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Flickering light, Photoreceptors, Cones