Context: Photobiomodulation (PBM) has been used to treat musculoskeletal injuries, reduce pain, heal tissue, and improve muscle performance and function. Many physiological effects of PBM therapy have been examined, but the thermal effects of PBM therapy have yet to be determined. Objective: To determine the superficial tissue heating characteristics of a Red and Blue combination light patch. Design: Controlled laboratory study. Setting: Research laboratory. Patients or Other Participants: Ten healthy individuals (M=5, F=5, age 22.2 ± 2.3, height (170.3 ± 13.1 kg). Interventions: Participants were positioned prone on a padded treatment table. While lying on the table, their posterior calf was cleansed before an IT-21 needle thermocouple was inserted 0.5 cm into the subcutaneous tissue. A PT-IT needle was secured to the posterior calf adjacent to the needle thermocouple. A second PT-6 thermocouple was secured to the skin 3 cm away from the treatment location. All thermocouples interfaced with an isothermex electrothermomitor. A single Careware Firefly (Carewear, Reno, NV) light patch was positioned over the subcutaneous and skin thermocouple within the treatment area. A 15 minute PBM therapy (wavelength=640 and 450 nm, average irradiance=3 m/W/cm2, peak power=9 mW, continuous peak power=3 mW, energy density=5.4 J/cm2, treatment area=50 cm2) was administered to the posterior calf. After the treatment, a 5-minute post-treatment temperature decay was recorded. Main Outcome Measures: Tissue temperature measurements from the thermocouples were taken every 1 minute throughout the 15-minute treatment and for 5 minutes post-treatment. Absolute tissue temperature and change from baseline temperature were used during the data analysis. A repeated measures ANOVA was used to determine if tissue temperature increased between the 3 measurement sites over the treatment time. Results and Conclusion: The red and blue wavelength combination photobiomodulation light patch significantly increases superficial tissue temperature. Thermal physiological effects may be an added benefit to this type of PBM therapy.