A low-cost three-wavelength illumination system for camera-based photoplethysmography imaging

This paper presents the design and implementation of a low-cost, reliable three-wavelength (3-λ) illumination device intended for photoplethysmography imaging (PPGI) measurements. The proposed system employs high-power light-emitting diodes operating in the green (520 nm), red (625 nm), and near-infrared (855 nm) spectral regions, enabling non-contact cardiovascular monitoring with flexible spectral configuration. The illumination module integrates seven green LEDs, eleven red LEDs, and fifteen infrared LEDs, a distribution selected to compensate for wavelength-dependent camera sensitivity while providing sufficient radiant intensity and spatial uniformity at low power consumption and cost. Each wavelength channel is independently driven using dedicated single-channel linear LED drivers with pulse-width modulation control, allowing precise adjustment of illumination intensity. System operation is managed by a microcontroller-based control platform, which ensures accurate timing, synchronization, and stable operation required for PPGI applications. The compact and modular design supports straightforward integration with camera-based imaging systems, while optional wireless control enhances usability in laboratory environments. Overall, the proposed illumination device represents a robust and cost-effective solution for experimental and applied PPGI measurements in research-oriented non-contact biosensing systems.