Development and validation of SLyM: a waterproof and low-cost sky luminosity meter

While Sky Quality Meters (SQMs) are vital tools for astrophysical research and monitoring light pollution, their adoption in Malaysian educational and research settings is hindered by high import costs and a lack of environmental durability. This paper introduces SLyM, a locally developed Sky Luminosity Meter engineered to provide a cost-effective and robust alternative to expensive commercial photometers. By utilizing an in-house fabrication approach with an Arduino-based architecture, the production cost of the device was reduced to roughly 10% of standard retail prices. Technological innovations in SLyM include a dual-layer sealing strategy - combining internal epoxy potting with a sealed 3D- printed PLA housing - to achieve full waterproof and weatherproof capabilities for reliable field deployment. To improve measurement precision, the design incorporates a built-in bubble level and a universal tripod mount, ensuring stable and accurate zenith-pointing alignment. Side-by-side performance validation against the industry-standard Unihedron SQM-LU confirms that SLyM produces consistent data trends, maintaining readings between 16.88 and 17.15 mag/arcsec2. Although a systematic calibration offset of approximately 0.55 to 0.60 mag/arcsec2 was observed due to differing spectral responses, SLyM demonstrated superior sensitivity to transient atmospheric events. It successfully captured real-time fluctuations, such as passing clouds and localized light intrusions, that were attenuated by the commercial unit’s narrower field of view. These results indicate that SLyM is a highly accessible and durable solution for astrophysics education and citizen science initiatives.