Why Don’t Your LED Bulbs Work With Motion Sensors?

You've installed new LED filament bulbs in a motion-activated security or utility fixture, but they're not working right. They stay dimly lit all the time, flicker erratically, or simply won't turn on at all, defeating the purpose of the sensor.

This problem is caused by the motion sensor itself, which often leaks a tiny amount of electricity to power its internal electronics. This "vampire draw" is too small to light an old incandescent bulb but is just enough to confuse the sensitive driver inside an LED bulb.

This isn't a theoretical problem; it’s a constant source of frustration for my clients. I remember a call from Jacky, a product manager for a large distributor in the US. He was supplying our G45 LED filament bulbs for a massive residential development project. The specs called for motion sensors on all garage, porch, and hallway fixtures for energy savings and convenience. A few weeks after installation, the complaints started pouring in from homeowners. The porch lights weren't turning off completely, casting a faint, spooky glow all night—a phenomenon often called "ghosting" or "glowing-when-off." The contractor blamed our bulbs, and Jacky was in a tough spot. I explained to him that the bulbs weren't defective; they were actually too efficient for the cheap motion sensors the builder had installed. The issue wasn't the bulb, but the sensor failing to create a true "off" state.

Isn't 'Off' Supposed to Mean Zero Power?

You assumed that when a motion sensor is in its "standby" or "off" state, it completely cuts all power to the light fixture. Now you're seeing bulbs that glow faintly, making you question the quality of the bulb or the sensor itself.

No, for many common motion sensors, "off" does not mean zero power. These sensors need to power their own internal circuitry and often do so by allowing a small leakage current to flow through the light fixture, even when it's supposed to be off.

This is the technical reality that creates 90% of all motion sensor compatibility problems. The root cause lies in the wiring and design of the sensor switch itself. To understand why leakage current exists, you need to look at how different types of motion sensors are wired into the wall. As a manufacturer, we have to design our bulb drivers to be as resilient as possible, but some sensors create a situation that is impossible for any standard LED bulb to handle correctly.

The Source of the Leakage: 2-Wire vs. 3-Wire Sensors

The problem almost always traces back to older or cheaper "2-wire" motion sensors that do not require a neutral wire for installation. This design makes them easy for homeowners to retrofit into existing switch boxes.

• 2-Wire Sensors (The Problem): These sensors are wired in series with the light bulb, just like a simple light switch. They have a "hot in" wire and a "hot out" (to the load). Since they don't have their own dedicated neutral wire to complete their own circuit and power their Passive Infrared (PIR) sensor and timer, they have to get power in a clever—and problematic—way. They do this by leaking a very small amount of current through the light bulb to the main neutral line constantly.
• 3-Wire Sensors (The Solution): Modern, higher-quality motion sensors are "3-wire" devices. They have a "hot in," a "hot out," and a dedicated neutral wire. This neutral wire allows the sensor to power its own internal electronics directly from the building's wiring, completely independent of the light bulb. When a 3-wire sensor is in the "off" state, its internal relay creates a true air gap, cutting off 100% of the power to the fixture. There is zero leakage current¹.

In Jacky's housing development project, the builder had used inexpensive 2-wire sensors to save on installation costs. The tiny leakage current was just enough to partially charge the capacitors in our LED bulb drivers, causing them to glow faintly. The problem was solved by replacing the 2-wire sensors with modern 3-wire versions.

Why Does This Leakage Current Only Affect LEDs?

You've used these exact motion sensors for years with old incandescent bulbs and never had a problem. Why do these issues of "ghosting" and flickering only appear now that you've switched to modern, energy-efficient LED filament bulbs?

It's because LED bulbs are incredibly efficient. An old 60-watt incandescent bulb needs a significant amount of power to start glowing, but a 7-watt LED has sensitive electronics that can be affected by even a tiny trickle of leakage current.

This is the irony of the situation, and it's what I explained in detail to Jacky. The problem isn't a sign of a bad LED bulb; it's a sign of a highly efficient one. The very thing that makes LEDs so great for saving energy also makes them susceptible to these low-power compatibility issues.

A Tale of Two Technologies

Let's look at the numbers.

• Incandescent Bulbs: A standard 60W incandescent bulb is a simple resistor. It needs a lot of power to heat its filament until it glows. The leakage current from a 2-wire motion sensor might be around 0.5 to 1.5 milliamps (mA). For a 120V circuit, this translates to less than 0.2 watts of power. This tiny amount is nowhere near enough to even begin to heat the filament of a 60W bulb. To the incandescent bulb, this leakage current is effectively zero, so it remains completely off.
• LED Filament Bulbs³: A 7W LED bulb is a different story. It doesn't have a filament to heat. It has a sophisticated electronic driver—a miniature computer—that converts AC power into the low-voltage DC needed by the LED chips. This driver is filled with sensitive components like capacitors and integrated circuits. The small but constant leakage current from the motion sensor is enough to slowly charge up the main capacitor in the driver. When the capacitor's voltage reaches a certain threshold, it tries to turn on the LED chips. However, there isn't enough sustained power, so it flickers briefly and then the cycle repeats, or it finds a state of equilibrium where it can power the LEDs very dimly. This is the "ghosting⁴" or "strobe" effect you see.

The LED isn't broken; it's just trying to do its job with the confusing, low-energy signal it's being fed by the incompatible sensor.

So, How Do I Fix This Compatibility Problem?

You need a reliable solution to get your motion sensors and LED bulbs to work together. You can't keep replacing bulbs, and you don't want to get into a dispute between the bulb supplier and the sensor manufacturer.

The best, most professional solution is to use motion sensors that are specifically designed for LED compatibility (3-wire sensors or those with adjustable settings). If replacing the sensor isn't an option, a simple load resistor can often solve the problem.

When Jacky presented the options to the home builder, he needed clear, actionable choices. Telling a builder to "use better parts" is not enough. You have to provide specific, cost-effective solutions. There are two primary paths to take, and we recommend the first one for all new installations.

Option 1: Replace the Sensor (The Best Solution)

This is the correct, permanent fix. For any new project, specifying the right hardware from the start is crucial.

• Use a 3-Wire Sensor⁵: As discussed, a sensor with a dedicated neutral wire provides a true "off" and will work flawlessly with any LED bulb. This should be the default specification for all new construction and professional renovations.
• Look for "LED-Compatible" Sensors: Many modern 2-wire sensors have been re-engineered to work better with LEDs. They may have a lower leakage current or internal adjustments. Look for dimmers that explicitly state compatibility with LED and CFL loads on their packaging or spec sheets. Brands like Lutron, Leviton, and others offer entire lines of sensors designed for this purpose.

Option 2: Add a Load Resistor⁶ (The Retrofit Solution)

In a situation where replacing hundreds of already-installed sensors is not practical or cost-effective, there's a workaround. You can install a small electronic component called a "load resistor" or "load-balancing resistor."

• How it Works: The resistor is wired in parallel with the light fixture (between the switched hot and neutral wires). Its job is to give the leakage current an alternative path to follow. The resistor is designed to have a low enough resistance to safely absorb the tiny leakage current from the sensor, but a high enough resistance that it doesn't waste significant energy when the bulb is actually on. By diverting the leakage current away from the sensitive LED driver, it keeps the driver from charging up and "ghosting."
• Considerations: This is an effective fix, but it's an added component that needs to be wired in at every problematic fixture. It adds a small amount of "vampire draw⁷" itself, slightly reducing the overall energy savings. At Hongyu Bulb, we can supply these load resistors as an accessory to help clients like Jacky solve problems on existing job sites where they are stuck with incompatible hardware. It's a pragmatic solution to a common problem.

For the housing development, the builder chose a mix of solutions. For all future phases, they updated their specification to a 3-wire sensor. For the existing homes with complaints, they had electricians install load resistors at the affected fixtures.

Conclusion

The conflict between LEDs and motion sensors stems from the sensor's leakage current, not a faulty bulb. Ensure compatibility by using modern, 3-wire sensors or retrofitting with a load resistor for reliable, ghost-free performance.