Performance Evaluation of Red Light-Emitting Diodes for Therapeutic Photobiomodulation Device Design

Introduction: Photobiomodulation (PBM) therapy relies on precise control of optical parameters such as wavelength, irradiance, and beam geometry to achieve therapeutic efficacy. Light‑emitting diodes (LEDs) are increasingly used in PBM devices due to their efficiency, cost‑effectiveness, and spectral flexibility, but their performance varies widely with device class, drive conditions, and optical configuration. This study aimed to experimentally characterize and compare the electro‑optical, thermal, and spectral properties of two commercially available classes of red LEDs—High Bright and Power—and to evaluate the effect of beam‑shaping optics on achieving PBM‑relevant irradiance at a clinically relevant distance. Material and Methods: Ten units of each LED class were tested under controlled laboratory conditions. Measurements included forward voltage–current characteristics, irradiance at 10 cm, thermal rise over time, and emission spectra (peak wavelength, full width at half maximum). The effect of integrating a 30° collimating lens with the Power LED was quantified in terms of irradiance gain. Results: At 10 cm, the High Bright LED produced sub‑therapeutic irradiance (<1 mW/cm²), whereas the Power LED achieved up to 0.72 mW/cm² without optics. The Power LED exhibited a narrower spectral bandwidth (16 nm) and higher radiant output but also a greater thermal rise (~28.6 °C in 180 s). Adding the collimating lens increased irradiance by more than thirteen‑fold across all voltages, enabling the Power LED to reach 10.64 mW/cm² at 2.3 V—within the PBM therapeutic range (10–50 mW/cm²). Unlike prior LED characterization studies that have primarily reported basic electro‑optical parameters, this work uniquely integrates irradiance, thermal stability, and spectral analysis under clinically relevant conditions and demonstrates that a single red Power LED combined with beam‑shaping optics can reliably achieve PBM‑therapeutic irradiance at a practical treatment distance. Conclusion: Power LEDs, when combined with appropriate beam‑shaping optics, can deliver PBM‑relevant irradiance at practical treatment distances using a single emitter. The methodology and findings are applicable to comparable AlGaInP red LEDs from multiple manufacturers and provide a framework for optimizing PBM device design across varying treatment distances and optical configurations.