Why are my LED high bay lights flickering?

Two usual culprits: the driver or the dimmer. Most LED high bays use a constant-current driver that needs clean input power. If you’ve got them on a 0-10V dimming system, a loose purple or gray wire at the controller or fixture end causes erratic flicker—especially when someone bumps the control box. Phase-cut dimmers (the cheap TRIAC ones from a hardware store) almost never work with LED high bays; they produce that strobe effect at low levels. Non-dimming fixtures on a switched circuit with a loose neutral in the junction box will also flicker as the connection heats up and cools down. Thermal shutdown is another real one: if the heatsink is caked with dust or the fixture is enclosed without airflow, the driver cycles on and off as it overheats.

Fix it in order. First, bypass any external dimmer temporarily—wire the fixture straight to line voltage. If the flicker stops, the dimmer is wrong for the load or the control wiring has a bad splice. Second, check the input voltage at the fixture with a meter; a sag below the driver’s minimum (like 100V on a 120V line) causes pulsing. Third, look at the driver label: some require a minimum load of 10% or they’ll flicker at the bottom end of dimming. If nothing else works, swap the driver. A failing electrolytic capacitor inside the driver is the most common hidden failure after two or three years, especially in cheap imports. Stay away from “universal” replacement drivers unless they match the exact current (mA) and voltage range of the original.