Nighttime light dynamics reveal peri-urban brightening and population decoupling in the Chengdu Chongqing megaregion.

Night-time light (NTL) composites offer a unique spatiotemporal view of urban growth by capturing electricity consumption, infrastructure density, and economic activity patterns that traditional land-cover surveys cannot fully reveal, yet inland China's megaregions remain understudied from this perspective. Using a 23-year (2000-2022) cross-calibrated NTL product integrated with land-cover, population, and topographic data, we analysed illumination dynamics in the Chengdu-Chongqing economic circle. Mean radiance rose by 78% while the lit area expanded from 0.53% to almost 12%. About three-quarters of this growth is confined to a 4-6 km peri-urban "neon ring" created chiefly by cropland conversion to high-rise housing and logistics estates, now ~ 40% brighter than historic cores. Targeted LED retrofits and façade-lighting curfews produced persistent downtown "dark hollows", proving that local policy can dampen sky-glow. Cropland-to-urban parcels emitted roughly 6 nW cm⁻² sr⁻¹ more light than other transitions, and protected wetlands brightened threefold, flagging covert development. Spatial autocorrelation analysis revealed extremely high global Moran's I values (> 0.92 after 2013), indicating strong spatial clustering patterns of illumination changes, with local LISA analysis identifying hotspots predominantly concentrated in the core areas of both cities. Projections indicate ~ 1,000 km² of additional luminous sprawl by 2042 as radiance continues to climb despite a 1.6% population decline, underscoring a widening decoupling between light and headcount.