Why do LED streetlights continue to emit a faint glow after being turned off?

When an LED streetlight continues to emit a faint light after being switched off—a phenomenon often referred to as "ghosting" or "afterglow"—the cause is generally similar to that of flickering, though it is most frequently due to the discharge of capacitors. Below are the specific causes and their corresponding solutions:

1. Discharge of internal driver capacitors: LED drivers typically contain input filter capacitors. After the power is cut, the stored charge in these capacitors is released slowly, causing the LED to remain dimly lit for a few seconds to nearly a minute. This is a normal occurrence; it does not affect safety or functionality and requires no action.

2. Reversed live and neutral wires: Similar to the cause of flickering, if the switch is wired to control the neutral wire instead of the live wire, the live wire remains connected to the driver. Through distributed capacitance, this allows enough current to flow to keep the LED faintly lit (without flickering). The wiring should be corrected.

3. Induced voltage: In cases involving long cable runs without shielding, an induced voltage may persist. This can be addressed by installing a bleeder resistor (e.g., a 220kΩ resistor connected in parallel across the input terminals of the light fixture).

4. Leakage due to moisture: In humid environments, insulation resistance can decrease, resulting in a small leakage current. Check the cable insulation and the sealing of junction boxes.

5. Leakage from smart switches: Some smart switches allow a small amount of current to flow even when turned off (to maintain communication functions). In such cases, connecting a resistor in parallel at the light fixture is recommended. A very faint glow—one that is barely perceptible and does not affect the surrounding environment—can generally be ignored. However, if the glow is noticeable and persistent, the root cause should be investigated and resolved.