Sightglass

A sight glass is a transparent window on pipes or tanks allowing visual inspection of fluids (level, flow, color) without interrupting the system, crucial in industries like pharma, food/bev, and oil/gas for monitoring conditions like pressure and contamination, working via light transmission and contrast, with advanced versions using special glass or internal indicators like floats. Another meaning refers to SightGlass Vision, a company creating spectacle lenses with Diffusion Optics Technology™ (DOT) to slow myopia progression in children by scattering light.