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Why The LED Slightly Illuminated After LED Light Fittings is Off?


Recently, there was a feedback from one of our customers, during the installation of the led light fittings, some strange phenomenon was found. The led slightly illuminated after led light fittings is off. What causes this phenomenon? Today we analyze the reasons and find the right solution.

led light pcb board

LED Light Fittings Knowledge

We all know that LED is a solid-state semiconductor device that converts electrical energy into visible light, a light-emitting diode that converts electricity directly into light. The core of the LED is a semiconductor light-emitting diode chip. One end of the chip attached to a bracket, one end is a negative pole. And the other end is connected to the positive pole of the power source so that the entire wafer is encapsulated by epoxy resin.

A single LED bead can only operate at low voltage (about 3V) and low current (about a few milliamps), and the light emitted is very weak. Many LED beads need to be connected in series or in parallel; at the same time, a single LED lamp bead is unidirectionally conductive (single-phase conduction of the diode). In order to make full use of the positive and negative half-cycle current of the alternating current, an integrated circuit chip needed. The AC 220V power supply is converted into voltage and current DC power to meet the power supply requirements of the LED lamp bead assembly so that it can normally emit light.

LEDs require less current and are sensitive to voltage and current. In use, they cause inductive illumination for a variety of complex reasons. In general, the reason for the faint light that causes the switch turn off is as follows:

led ceiling lamp
led panel light

1. The neutral line in led light fittings is electric

This is the most common situation.

because the plumber enters the lamp base directly when the plumber is in the line, and the neutral line enters the control switch. This causes the switch to be disconnected, and the live line still has current passing through the light to the side of the switch, causing the light to be slightly bright.

Solution: Adjust the wiring and let the switch control the live line.

Because the electrician connected the wrong line when the main gate entered the line, the live line and neutral line were reversed. This accidentally reversed all the live and neutral lines, causing all the switches to control the neutral line.

Solution: You can solve the problem by adjusting the incoming line.

led lamp connection
led lamp connection

③If the switch controls the live line and used the traditional mechanical wall switch. But the led still slightly illuminated, that is because the neutral line is electric. Neutral line electricity is a common phenomenon. If the neutral line does not well grounded, the three-phase load of the transformer unbalanced, the line is too long, the wire diameter is thin, or the neutral line current is too large, which all these will cause the neutral line to electric.

Solution: Re-neutral grounding or low-voltage retrofit (this requires the property to be solved by the power supply company).

2. Double control switch in led light fittings has a wiring error

There are several ways to connect the two-control switch. If the wrong connection is used, the traditional incandescent lamp will not be bright, but for the LED lamp, because it is DC, it will be slightly bright after turning off the led light fittings.

Solution: Install the normal control FireWire connection and rewire.

Wiring method of dual control switch: single double control switch, there are three contacts at the back, which are L, L1, L2. Connect the two L1 and L2 respectively, the live line connected to the L contact point of a dual control switch, and the neutral line connected to the L contact of the other dual control switch.

led lamp connection
led lamp connection

3. Switch with indicator light, using electronic type, touch switch

There is an indicator light inside the switch, and a slight current will flow after the led light fitting is turned off.

Electronic touch switch
led neon light

4. Non-isolated driver, light source patch, and substrate leakage

Many luminaires are driven by inferior quality and resistive voltage for cost reasons, or the quality of the light source chip is poor, and there is leakage of the chip and the substrate. Substrate copper and substrate capacitance effects can also cause light leakage. This is why in a room, some lamps have high brightness and some have low brightness.

Solution: change the lamp

If the led light fitting uses an electronic touch switch, such as infrared, voice control, remote control switch. There will also be a shimmering phenomenon after turning off the lamp.


①Change the switch.

②Parallel 500K resistors in the incoming line of the lamp. But this method professional technicians measure the installation, non-professionals are best not to operate casually. And this method is ineffective for the neutral line electricity or the dimming caused by the leakage of the patch.

led tubular tri proof light
led industrial lighting

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