LED Flicker Only With Dimmer Off Decision Tree

Why this matters

LED fixtures that flicker when a switch is OFF (the "ghost glow" or "phantom flicker") are not a fixture defect. They are responding to milliamps of leakage current that incandescent loads consumed silently and that LEDs cannot. The source is almost always a smart switch needing a neutral, a 3-way wired with a shared traveler, a dimmer with capacitive leakage, or a damaged neutral creating an induced potential on the switched hot. ANSI/IEEE 1789-2015 sets flicker thresholds for human perception, and ghost-glow flicker often falls below 8 Hz where it is most annoying. The decision tree is short but the wrong call sends the homeowner back to the fixture aisle for the third time.

Symptom presentation

Verify the flicker happens with the switch OFF. Cycle the switch and watch. A truly OFF fixture should be black. Faint pulsing, a barely-visible glow, or a periodic flash every few seconds with the switch off is the ghost-current symptom. If flicker only happens with switch ON and dimmer at low setting, this is a different problem; that is dimmer compatibility, not ghost current.

Document the fixture type and the switch type. A non-dimming LED bulb on a non-dimming switch should never ghost; if it does, the switch is bad (welded contact, smart switch, or 3-way miswire). A dimmable LED on a dimmer is the most common ghost-glow case because nearly every dimmer leaks 1 to 5 mA in the OFF position through its sensing circuit.

Quick checks

Pull the switch and identify it. If it is a smart switch (Lutron Caseta, Leviton Decora Smart, Kasa, Eve, Inovelli) and has no neutral connection, you have found the cause. Smart switches without a neutral steal current through the load to power their wireless radio, and any LED downstream will glow on that bleed. NEC 2023 Article 404.2(C) requires a neutral at the switch box for most new installations specifically to support smart switches; older boxes need either a neutral pulled or a switch designed for no-neutral operation with bleeder resistor.

If a standard dimmer is installed, check whether it is the right type for the LED. Forward-phase (leading-edge) dimmers were built for incandescent and are wrong for most modern LEDs; they leak more current at OFF. Reverse-phase (trailing-edge) ELV dimmers leak less and are the right pairing for modern LED drivers. Lutron Diva LED+ and Leviton Decora Edge are common trailing-edge models that solve most ghost cases.

Isolation tree

Measure leakage. With the switch OFF and the bulb in place, clamp an AC mA meter on the switched conductor. A leakage of 0.5 to 2 mA is normal for a dimmer in the OFF position. Above 2 mA points to a smart switch on no neutral, a 3-way with a downstream switch loop creating a capacitive divider, or a damaged neutral creating an induced potential on the hot.

If leakage is high and there is a smart switch with no neutral, the fix is to pull a neutral to the box or install a bypass capacitor (Lutron LUT-MLC, Caseta Wallbox accessory) at the fixture. The bypass adds a load that absorbs the steal current so the LED stays dark.

If leakage is low (under 0.5 mA) and the LED still glows, the LED driver itself is unusually sensitive. Some Philips and GE LED bulbs designed for 4-pin direct-wire fixtures glow on as little as 0.2 mA. Swap to a known low-flicker bulb (Cree A19, Philips Ultra Definition, Hue White if smart) and re-test.

For 3-way circuits with persistent ghost glow, trace the wiring. A 3-way with a shared traveler that crosses the path of the home-run cable will couple capacitively into the OFF state. The fix is to re-route the traveler away from the home-run, or to install a neutral-required 3-way smart switch kit (Lutron Pico companion or Leviton DD0SR companion) that does not leak.

Confirming diagnosis

Force the fix. Install the proposed remedy (bypass capacitor, neutral pull, dimmer swap, bulb change) and re-test with the switch OFF for 30 minutes. Confirm zero glow at the fixture and no flicker on the test light. If the ghost returns at a different time of day, look for a fluorescent fixture or motor on a nearby circuit inducing into the run; LED fixtures in unconditioned spaces (garages, attics) are especially sensitive to induced potential from nearby HVAC condenser cabling.

For flicker investigations, ANSI/IEEE 1789-2015 provides the low-risk and no-effect thresholds. A bulb pulsing visible to the eye at 1 to 8 Hz is high-risk; a fix is mandatory, not optional.

Remediation

For smart switch on no neutral: pull a neutral if the wall is open, or install a bypass capacitor at the fixture. For wrong dimmer type: swap to a trailing-edge LED-rated dimmer. For damaged neutral or 3-way coupling: re-pull the cable or re-route the traveler. For bulb sensitivity: change brand to one with documented low flicker (specifications on package or driver datasheet).

After remediation, document the bulb brand and the switch model on the panel directory or in the fixture spec sheet so a future bulb swap does not reintroduce the symptom. Mixing brands on a 6-bulb chandelier is the third most common callback cause.

References

• NEC 2023 Article 404.2(C) (neutral required at switch boxes for general lighting)
• ANSI/IEEE 1789-2015 (Recommended Practice for Modulating Current in High-Brightness LEDs, low-risk and no-effect flicker thresholds)
• UL 1472 (Solid-State Dimming Controls, OFF-state leakage current limits)
• UL 8750 (Light Emitting Diode (LED) Equipment for Use in Lighting Products, driver compatibility)
• Lutron Application Note 47 (Eliminating Phantom Glow in LED Loads)