Have you ever noticed that when you turn off your LED lights, some still emit a faint glow? This common effect is known as “LED ghosting” or “afterglow,” and it can be puzzling or even frustrating when it lingers.
But what causes this phenomenon? Many research studies have suggested that afterglow typically results from residual energy stored in the LED driver, capacitive coupling in the wiring, or even current leakage—allowing the LED to remain dimly lit even when switched off.
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LED Lights Glow When Switched Off
After switching to LEDs or when replacing a faulty LED lamp in some cases the LED continues to glow weakly after turning the light switch off. Observing this effect the first time could be very surprising 🙂 The light switch is in the off position and the LED lamp continues to glow. In most of these cases the LED just lights up very weakly but also this could be annoying if the luminaire is mounted in your bedroom for example.
Here are a few reasons as to why you might be experiencing an afterglow even after turning off the lights.
- in the phosphor layer
- in the LED driver
- Electronic dimmer
- Light switch with night light
- Switched neutral conductor
- Parallel cable routing
LED Light Stores Energy
The first two reasons can be found in the LED light itself. You can easily check this by removing the light bulb from the socket immediately after turning off the light switch. If the bulb continues to glow weakly after removal, it is due to the luminescent layer or the LED driver. However, if the lamp goes out immediately when it is removed from the socket, the cause must be found in the electrical installation.
Glowing of the luminescent layer
To produce white light, blue light-emitting diodes are used with an additional luminescent layer (phosphor layer). Depending on the semiconductor material used, the luminescent layer can store a certain amount of energy in the form of visible light for a certain period of time. According to its wattage this leads to the afterglow effect from a few seconds to several minutes.
Afterglow of LED driver
LED bulbs and luminaires are equipped with an electronic circuit called an LED driver. This generates the operating current required for the LED (light emitting diode). The driver contains various components including capacitors and inductors. These components can serve as a storage for electrical energy.
Depending on the design of the driver circuit, these components may still be active when the input voltage is switched off by pressing the light switch. As a result the LED continues to light until the energy stores are discharged. This can also take from a few seconds to several minutes.
Caused by the Electrical Installation
If you have found out with the test mentioned before that the afterglow is not caused by the lamp itself, the electrical installation is to blame. In this case the LED continues to glow permanently when the light switch is turned off. This may be due to the type of light switch or dimmer or an incorrectly connected switch. Even an unfavorable cable routing can be responsible for the glow.
The afterglow issue is usually only visible after converting from old light bulbs to LEDs. Any leakage currents and induced voltages were simply short-circuited by the filaments of the old lamps. However these are sufficient to make an LED light glow weakly.
Electronic dimmer
Many older electronic dimmers were designed for incandescent or halogen bulbs and required a minimum load to function properly. LED bulbs, on the other hand, are more energy-efficient, but they often don’t meet this load requirement, preventing the dimmer from fully cutting off power.
As a result the LED continues to glow weakly.
- Check the minimum load of the old dimmer and compare it with the LED lights used
- If the minimum load is not reached, only the replacement with an LED dimmer will help
- Check out this Lutron dimmer
Light switch with night light
Depending on the light switches you are using, some might already come with a built-in night light, causing users to experience small glow lamps — in older designs, these were wired in series with the main light fixture.
When you switch to LEDs, the high resistance from their power supply unit can create a small current that passes through your LEDs, causing them to glow slightly in the dark.
- Disconnecting the glow lamp should prevent the LED afterglow effect
- Replacing the switch with a variant with an additional connection with a neutral conductor
- A widely used model is this Kasa switch
Switched neutral conductor
A single-pole light switch normally switches the phase (L) in the line to the ceiling lamp. If the electrical wiring is not done professionally, the neutral conductor (N) is sometimes switched instead of the phase.
In this case capacitive and inductive effects can still ensure that a low voltage between the live phase and the switched-off neutral conductor is applied to the LED lamp. This voltage is sufficient for the LED to glow weakly.
- Check the neutral conductor and phase for the correct connection
- If the LED is still glowing, use a two-pole light switch like the Leviton 5622-2W
Parallel cable routing
In some houses, two-way light switches are installed in areas like staircases or hallways, with their wiring running in parallel over a long distance.
The voltage-carrying conductor can induce voltage in the inactive wires and give them enough energy to make the bulb glow faintly.
- Check the wiring of the two-way circuit
- Install a bypass capacitor in the ceiling light
- In many cases a Lutron LUT-MLC will help
Conclusion
Even though these afterglows are usually harmless and can be addressed by either replacing the bulb or fixing your dimmer, that isn’t always the case. If you are experiencing LED ghosting, it might be because of faulty wiring and needs immediate attention from a professional electrician, allowing you to prevent any major issues.
