A Solid-State UV-B LED Phototherapy Device: Hardware Design, Optical Characterization, and Electronic Control for Localized Skin Treatment

This work presents the design and characterization of a portable UV-B phototherapy system based on 308 nm LEDs, intended as a compact and mercury-free alternative for vitiligo treatment. Optical measurements showed a narrow emission centered at 308 nm, with stable spectral behavior and an optical power of approximately 1 mW at the treatment surface, comparable to conventional mercury and excimer lamps but without their associated environmental and thermal issues. A matrix of nine AlGaN UV-B LEDs was used to improve illumination uniformity and compensate for the lower output of individual devices. The electronic system includes an operational amplifier, a MOSFET driver, and a GaN photodiode-based transimpedance amplifier (TIA), allowing real-time UV-B monitoring and closed-loop intensity control. An FPGA-based interface enables precise adjustment of exposure time, duty cycle, and LED selection for localized treatment. Moreover, the system is inherently scalable, as the irradiation area and output power can be increased by adding more LEDs without major changes to the control system. The biological evaluation indicated that UV-B exposure did not affect fibroblast viability under recommended conditions, while signs of DNA damage appeared only at higher intensities and longer exposure times. These results suggest that the system can be used safely within controlled limits. Future work will focus on dose–response studies in clinically relevant models to assess therapeutic effectiveness.