Carbon dots (CDs) have been developed as prospective nanomaterials for sensing applications owing to their cost-effectiveness, thermal stability, low toxicity, and unique luminescence properties. CDs sensors have been widely used for ion detection but rarely for light detection. Herein, fluorescent CDs from carbon black containing refilled blue ink has been prepared by a solvothermal reaction-assisted straightforward one-pot route under mild temperature conditions. The body color of the as-prepared CDs solution is light brown and shows blue emission under ultraviolet (UV)-light excitation. The UV-light detecting film has been developed by blending the CDs/poly(vinyl alcohol) solution and examined its sensitivity with the increase of UV-light irradiation time. The progression in the body (light-brown to purple) and emission (blue to orange) colors are distinguishable and demonstrates their feasibility in developing the high-performance CDs-based UV detectors.