LED-Based Photometric Systems for Decentralized Chemical Analysis: Applications, Design Considerations, and Practical Limitations

Photometric methods are essential in analytical chemistry for environmental, biological, and industrial monitoring. Conventional spectrometers rely on deuterium or tungsten lamps, which are bulky, energy-intensive, and costly to maintain. Advances in light emitting diode (LED) technology have enabled compact, energy-efficient, and cost-effective alternatives for portable and decentralized chemical analysis. This review provides an application-oriented synthesis of recent developments in LED-based photometry, systematically comparing major analytical fields to identify common design strategies, recurring performance limitations, and emerging trends. Representative applications include environmental monitoring, point-of-care diagnostics, food quality control, industrial process analysis, and STEM education. Design-related aspects, including optical layouts, detector selection, wavelength matching, and calibration strategies, are discussed where they influence analytical performance and practical implementation. Recent innovations, such as multi-wavelength LEDs, 3D-printed housings, and microcontroller-based systems, have further expanded the accessibility and adaptability of LED-based photometers. Across the reviewed studies, progress has been driven primarily by translating established photometric methods into compact, application-specific platforms rather than by developing new analytical assays. Despite these advances, challenges remain regarding sensitivity, calibration robustness, validation, and methodological standardization. By identifying cross-cutting challenges and successful implementation strategies, this review provides guidance for the future development of robust, low-cost, and reliable LED-based photometric systems for decentralized chemical analysis.