This is a prospective randomized clinical trial study to investigate two main aspects. The first aspect is to investigate the efficacy exposure to green light emitting diode (GLED) in reducing postoperative opioid medications requirements by 20% as the primary outcome amongst patients scheduled for elective total knee replacement surgery (knee arthroplasty). The second aspect is to reduce postoperative pain by 30%, improve preoperative anxiety by 30%, and improve the quality of sleep pre and postoperatively by 30%.

Seventy participants scheduled for elective unilateral primary total knee arthroplasty (total knee replacement) will be recruited from the pain clinic or from the orthopedic surgery clinics at Banner-University Medical Center by the pain or orthopedic physicians who are key personnel of this study. Once a participant is identified, he/she will meet with one of the research team members to explain the nature of the clinical trial and undergo a standard of care medical history gathering and baseline physical examinations. If the participant meets all the inclusion and have no exclusion criteria, he/she will be presented with a written consent in English to explain all the risk and benefits of this clinical trial. Once a participant signs a consent, he or she will be randomized by the study statistician, in a 1:1 ratio to either a GLED group (treatment) or white light-emitting diode (WLED) group (control). The participant will be trained on how to use the light device by one of the research team members. All participants will be exposed to either GLED or WLED for 8 weeks prior to surgery and two additional weeks after surgery.

Participants who meet inclusion and exclusion criteria will be enrolled into the study after consenting. Patients will be interviewed and asked to provide their history of present conditions, past medical history, if they are on disability or receiving compensation for an injury, demographic information, and ethnic group (determined by self-identification). Additionally, patients will undergo a physical examination. The focus will be on the history of colorblindness and chronic pain. A pain assessment will be conducted, and this will be obtained verbally from the patient. Physical examinations will be obtained at the initial study visit and will be documented in the source documents.

The participants will be instructed to use the GLED or the WLED devices as follows:

Before surgery - The participants will be instructed to choose rooms in their home. These rooms must be dark and has no other source of light except the light device provided. The participants will be instructed to place the devices in their fields of vision and keep it between 3 feet away from their eyes. This distance is chosen based on the intensity of the light from our clinical trial, which corresponds to 100 lux. The participants will be asked not to stare directly at the light, but to rather allow it to enter their eyes from the periphery and to treat it as they would treat any other light fixture. The participants will be asked to have 2 hours of exposure every night. Given that participants may have different preferred time to go to bed, we will ask them to start the exposure any time after sunset when sunshine is no longer illuminating their chosen rooms for exposure. We will encourage the participants to participate in any activities that do not require additional lights so they do not fall asleep during the nightly light exposure. For example, the participants may enjoy reading (100 lux provide enough illumination for reading), listening to music, exercising, etc. The participants will be exposed nightly to their light for 8 weeks prior to surgery.

After Surgery - On average, half the participants may be discharged home from the hospital after they recover from anesthesia in the same day. The other half of the participants may be admitted to the hospital for 1-3 days on average based on their medical profile, the course of the surgery, and any complications or concerns of the surgeons or the anesthesiologists. For patients that will be discharged home on the same day, they will continue light exposure as they did before surgery. For patients who may be admitted to the hospital, we have already secured the approval from the hospital administrative staff as well as the nursing manager to allow the participants to utilize the light devices in the patients' rooms. The light devices were examined by the Facility Management (for electrical hazards) and Infection Control and both approved the use of the light devices in the hospital setting. The participants will place the light devices in their fields of vision in the patients' rooms. Patients and nurses are able to control the ambient lights in the rooms and it will be kept dark except for the light from the light devices for two hours every night. The participants will be exposed to the light for 2 hours in the evening prior to sleeping. If the surgery is scheduled late at night or if the participants has a slow emergence from anesthesia, they may not be awake during the first night in the hospital to have the light exposure. Once participants are discharged from the hospital, they will continue exposure to the light as they did before surgery for the remainder of the two weeks postoperatively.

Data Management:

Data will be collected on standardized case report forms and entered into a HIPPA-compliant electronic database (e.g. Microsoft Access) that provides an appropriate interface with a robust statistical package . All study-related hard copy materials will be stored in locked file cabinets.

Inclusion Criteria:

1. Male or female 18 years or older
2. Scheduled for elective primary knee replacement surgery
3. Able to understand, read, and write English

Exclusion Criteria:

1. History of chronic pain requiring chronic opioids equal or greater than 90 Morphine Milligram Equivalent (MME)/day
2. Severe psychological or psychiatric conditions
3. Unanticipated surgical complications, such as prolonged bleeding requiring long hospital stay, infection, dehiscence, and airway complications (anesthesiologist unable to extubate secondary to pulmonary complications
4. Surgery cannot be postponed eight weeks from the day of recruitment
5. Colorblindness
6. On disability, involved in a legal case pending, or receiving compensation for a work-related injury