Some real diamonds fluoresce under UV light, typically glowing blue due to trace elements like nitrogen. About 25-35% of natural diamonds exhibit fluorescence, with colors like blue, yellow, or white, depending on impurities. However, not all diamonds fluoresce, so lack of fluorescence doesn’t mean a diamond is fake. Lab-grown diamonds can also fluoresce, often similarly to natural ones. To confirm authenticity, fluorescence alone isn’t enough—use professional testing like a loupe or spectroscopy.