Green Light Exposure in Healthy Volunteers Exposure in Normal Human Volunteers

Investigating the Analgesic Effects of Green Light Exposure in Normal Human Volunteers

This research project is intended to understand the mechanisms of action for the pain-relieving properties of visual green light exposure.

The investigators have shown previously that greenlight exposure decreased acute and chronic pain in both animals and humans. However, the investigators do not yet understand how green light exposure is capable of such function.

Study Overview

• Status: Active, not recruiting
• Conditions: Chronic Pain
• Intervention / Treatment: Device: Green Light Emitting Diode; Device: White Light Emitting Diode

Detailed Description

Pain is a biological function. There are several pain centers in the brain that modulate the intensity of the pain signal perceived by the brain. Part of the modulations takes place through two separate pathways. The first pathway mediates pain signals and is known as the ascending facilitator pain pathway. The main function of this pathway is to relay the pain signal to the brain to be processed.

The second pathway is known as the descending inhibitory pain pathway. The main function of this pathway is to inhibit the pain signal mediated by the first pathway.

Normal humans typically have a balance between the activities of the ascending and descending pain pathways.

The investigator animal studies suggest that green light therapy exhibits its pain-relieving effects through altering the balance between the ascending and descending pain pathway in a manner to result in an overall reduction or normalization in pain perception.

To test this hypothesis, the investigators propose recruiting 30 healthy human volunteers. The participants will be equally randomized into either green light (treatment) or white light (control) exposure groups. The investigators will initially test the activities of the ascending and descending pathways using thermal and mechanical stimulations. The investigators will also test brain wave activities using a non-invasive EEG device. After establishing the baseline activities of the pain pathways and brain waves, the volunteers will be exposed to the green light or white light at low intensity (4-100 lux) for two hours in our laboratory. After two hours of light exposure, the investigators will again test the activities of the pain pathways using thermal and mechanical stimulation and measure the brain wave EEG activities.

• Study Type: Interventional
• Enrollment (Estimated): 30
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Arizona
    • Tucson, Arizona, United States, 85724
      • Banner University Medical Center Tucson

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 50 years (Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

1. 18-50 years healthy men or women
2. Able to speak and understand English
3. No history of Chronic pain
4. No known neuropathies in areas that testing will take place, (forearms, muscle at the base of thumb on the palm of the hand and upper back/shoulder area.

Exclusion Criteria:

1. Serious mental illness defined as distortions of perception, delusions, hallucinations, and unusual behaviors resulting in loss of contact with reality. This will be assessed during the screening interview.
2. Colorblindness or uncorrected cataracts.
3. Tissue damage in areas that testing will take place, (forearms, muscle at the base of the thumb on the palm of the hand, and upper back/should area.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Green Light Exposure; Subjects will complete thermal and mechanical pain threshold detection tests and Electroencephalography (EEG). After completion, subjects will be exposed to a green light-emitting diode for two hours. After exposure, thermal and mechanical pain threshold assessments and Electroencephalography (EEG) will be conducted.	Device: Green Light Emitting Diode; GLED exposure for two hours; Other Names: GLED
Placebo Comparator: White Light Exposure; Subjects will complete thermal and mechanical pain threshold detection tests and Electroencephalography (EEG). After completion, subjects will be exposed to a white light-emitting diode for two hours. After exposure, thermal and mechanical pain threshold assessments and Electroencephalography (EEG) will be conducted.	Device: White Light Emitting Diode; WLED exposure for two hours; Other Names: WLED

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Ascending Pain Pathway	Changes in activity of the ascending pain pathway	Two hours
Descending Pain Pathway	Changes in activity of the descending pain pathway	Two hours

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Delta Brain Activities	Changes in the baseline of Delta waves of EEG	Two hours
Theta Brain Activities	Changes in the baseline of Theta waves of EEG	Two hours
Alpha Brain Activities	Changes in the baseline of Alpha waves of EEG	Two hours
Sigma Brain Activities	Changes in the baseline of Sigma waves of EEG	Two hours
Beta Brain Activities	Changes in the baseline of Beta waves of EEG	Two hours

Collaborators and Investigators

• Sponsor: University of Arizona
• Investigators: Principal Investigator: Mohab Ibrahim, PhD, MD., University of Arizona

Publications and helpful links

General Publications

• Ibrahim MM, Patwardhan A, Gilbraith KB, Moutal A, Yang X, Chew LA, Largent-Milnes T, Malan TP, Vanderah TW, Porreca F, Khanna R. Long-lasting antinociceptive effects of green light in acute and chronic pain in rats. Pain. 2017 Feb;158(2):347-360. doi: 10.1097/j.pain.0000000000000767.

Study record dates

Study Major Dates

• Study Start (Actual): June 14, 2022
• Primary Completion (Estimated): December 31, 2026
• Study Completion (Estimated): December 31, 2026

Study Registration Dates

• First Submitted: February 22, 2022
• First Submitted That Met QC Criteria: March 16, 2022
• First Posted (Actual): March 25, 2022

Study Record Updates

• Last Update Posted (Actual): January 5, 2026
• Last Update Submitted That Met QC Criteria: December 29, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Pain; Neurologic Manifestations; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Chronic Pain
• Other Study ID Numbers: 00000370

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No