Effect of Green Light Exposure at Different Times on the Pain of Subjects

The study consisted of two components. In the healthy-volunteer component, participants underwent a 30-min green-light exposure at three different times of day (08:00-09:00, 12:00-13:00, and 16:00-17:00) on separate days in a within-subject design, with a washout period of at least 2 days between sessions. Pain threshold, pain tolerance, and cold pain sensitivity were assessed before and after each exposure.

In the surgical component, eligible patients were randomly assigned in a 1:1 ratio to either the green-light intervention group or the sham-device control group using a computer-generated random sequence. Participants wore identical wearable GLED glasses for 30 min before arterial puncture and throughout surgery. In the intervention group, the device delivered 511-515 nm green light at 100 lux; in the control group, the device remained powered off and participants were exposed only to ambient room light. Care providers, investigators not involved in intervention administration, and clinical outcome assessors were blinded to group allocation. Personnel responsible for device allocation and administration were unblinded and were not involved in perioperative clinical care or outcome assessment.

Inclusion criteria

Healthy volunteers:

• Age 18-65 years.
• ASA physical status I.

• Age 18-65 years. 2. ASA physical status I-III. 3. Scheduled for elective abdominal surgery under general anesthesia requiring arterial puncture.

Exclusion criteria

：

• Skin ulceration, dermatitis, or allergic reactions at the study site.
• Chronic use of analgesics or psychiatric medications.
• Color blindness or uncorrected cataracts.
• Severe cardiovascular, respiratory, or inflammatory diseases.
• Failure of the initial arterial puncture attempt (surgical cohort only).
• Inability to communicate or provide informed consent.