RESEARCH ON THE GENERATION AND OPTICAL CHARACTERISTICS OF INDOOR STRIP AND ARCHED RAINBOWS BASED ON WATER PRISM

This study presents a controllable method for generating indoor rainbows via water-based triangular prisms by adjusting the curvature of the bottom surface of water-filled rectangular glass aquariums. Bright meter-scale striped rainbows (vertical width: 1.0m, horizontal width: 36.0cm) and large-span arched rainbows (horizontal span: 4.0 m, arch height: 2.0m, spectral vertical width: 36.0cm) are successfully projected. The rainbows originate from solar spectra formed by refraction-reflection-refraction (RRR) processes at air-water interfaces, with their morphologies precisely regulated through geometric optical parameters: striped rainbows exhibit a red-top-violet-bottom distribution, while arched rainbows mimic natural rainbows with red-outer-violet-inner curvature. Based on a ray-tracing model, the quantitative effects of solar altitude angle (α=55°), aquarium inclination angle (θ=2.8°～9.0°), and acrylic glass substrate arch height (h_a=1.5～3.5cm) on rainbow dimensions are systematically revealed. TracePro simulations validate the light intensity distribution and true-color reproduction, showing a maximum irradiance of 1.01 W/m² for arched rainbows under an effective light-entry area of ～9.0cm² at a projection distance of 6.4m. Theoretical predictions suggest that enlarging the aquarium size while optimizing curvature can further enhance brightness to practical application levels. Notably, a counterintuitive optical phenomenon is observed where reversed bending of the acrylic substrate generates upward-arched rainbows, with light from the left side of the curved substrate forming the right side of the arched spectrum. This work provides an innovative solution for visualizing complex dispersion effects in science education and establishes an experimental foundation for architectural optical decoration and artistic projection technologies.