Scan chain diagnostics have become more important than ever due to the increasing complexity of VLSI designs, as more and more scan latches/flip-flops are utilized in designs, especially in microprocessors. At the same time, the off-state leakage current of CMOS technology grows exponentially from one generation to the next one. This fact imposes a big challenge on the chip design, packaging, cooling, etc. However, innovative applications, based on the detection of Light Emission due to Off-State Leakage Current (LEOSLC) have been developed for testing and diagnosing modern VLSI circuits. In this paper, we show that LEOSLC can be used to effectively debug, diagnose, and localize defects in a broken scan chain.