Design of a multi - wavelength high irradiance LED phototherapy system for LLLT

Low level light therapy (LLLT) is a fast-growing technology used in noninvasive therapies which can stimulate healing and relieve pain and inflammation. The introduction of light-emitting diode (LED) devices has reduced many of the concerns associated with halogen lamp and lasers, such as expense and safety. However, many LED devices are bulky and not designed for home use. Besides, the effectiveness of the treatment by LLLT has significant variations in terms of dosimetry parameters for the used LED, such as wavelength, irradiance or power density, energy, etc. Therefore, we design a home-used multi-wavelength LED phototherapy system with the advantage of a small volume and high irradiance in this paper. By using AlN ceramic substrate and copper substrate as composite substrate, the vertical structure chip is tightly attached to the ceramic substrate circuit, then the package of the four-wavelength chip module is completed. In order to distribute the irradiance of all four different spectra over the desired target area, an optical mixing rod is used to collect the light, and the light is all reflected into the output face of the optical mixing rod through full internal reflection. Additionally, to form a light spot of 50mm in diameter at a distance of 5cm from the output surface, we design a pair of lens with a short focal length and large field of view based on Kohler illumination method. The parameters of the lens are designed by the software of ZEMAX. The hardware circuit uses the STM32F104 processor as controller and constant current drive mode to ensure the quality of LED light. An experimental prototype is established, and the irradiance and its uniformity, stability and safety of the phototherapy system are tested. The experimental results show that the maximum irradiance of the system is 115.4mW/cm2, and the uniformity reaches 88%. After the phototherapy system works for 2 hours with maximum illumination, the irradiance deviation is 6.7% and the temperature rise of the system is 19°C.