Editorial Technical Reference

Indicator lights that stay dark when switched off (LED pilot lights on AC circuits, residual voltage and the voltage threshold)

LED panel indicator lights on AC control circuits · an LED that stays faintly lit when its circuit is switched off, residual voltage and leakage current, LED blocks with no resistor, external resistors found with a potentiometer, and heads with a built-in voltage threshold such as 60 V anti-inductive voltage

Schneider Electric's support notes describe LED pilot devices that light up when the device is off because of residual voltage or leakage current in the circuit, which shows the operator a state that is not there. Whether a given light does this depends on how its LED block is built, so the pilot light is specified with that in mind.

LED panel indicator (pilot) lights for control panels and machines, specified so they stay off when their circuit is off. Signal towers, colour meanings and panel hole sizes are covered on the Status indicators: signal towers, indicator lights and audible alarms page; PLC output types on the Output module for PLCs: choosing relay or transistor outputs by load, switching rate and how inductive loads are clamped page; solid state relays on the Solid state relay (SSR) page; emergency stop devices on the Emergency stop button page; washdown operator panels on the Stainless steel washdown HMI for food and beverage lines page.

CNFX editorial research · Sources checked October 13, 2026 · 4 sources

Why an LED glows when off Resistor or threshold head

Stainless steel panel box with five lit round indicator lights in metal bezels, green, amber, red, blue and white, and six cable glands with black cables along the bottom — Five metal-bezel indicator lights on a stainless panel box

Start with your task

Why an LED glows when offResidual voltage, leakage. Resistor or threshold headFixes the makers give.

Why an LED pilot light can glow when its circuit is off

Schneider Electric's support note FA112098, for 30 mm push buttons and Type K and SK standard LED light modules (Harmony 9001K and 9001SK), addresses residual voltage or leakage current that makes the LED in an illuminated pilot device light up when the device is off. [1]

A second Schneider note, for the 120 V pilot light 9001KP38LG, states that it contains only an LED block for a 120 V indicator light, with no resistors, and says the answer applies "If you are facing issues due to leakage current". [2]

Tell the supplier what drives each light (relay contact, triac or transistor output, or a contact with a suppressor across it), the control voltage, and the cable run, and ask whether the light will stay dark with that driver open.

An external resistor, or a head with a voltage threshold

For the 30 mm range, Schneider recommends adding resistance to the circuit to suppress residual voltage large enough to light the LED. It gives no value: it suggests fitting a potentiometer temporarily, increasing it until the false illumination stops, reading the resistance, and fitting a fixed resistor of that value. [1]

For the 120 V 9001KP38LG, Schneider names two options: adding resistors externally, or using its 22 mm diameter range, which has a voltage threshold. [2]

ABB describes its CL2 compact pilot lights (for example CL2-623G green and CL2-623L blue) as "LED 230V AC with 60V anti-inductive voltage". [3] [4]

Product	What the maker states	Source
Schneider 30 mm Type K/SK LED modules	Add resistance; find the value with a potentiometer	[1]
Schneider 9001KP38LG, 120 V	LED block only, no resistors; external resistors or 22 mm range with voltage threshold	[2]
ABB CL2-623G / CL2-623L	LED 230 V AC with 60 V anti-inductive voltage	[3] [4]

Ask each supplier whether the LED head has a voltage threshold and at what voltage, and if a resistor is needed, its value and power rating at your control voltage.

LED indicator light details

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Control voltage: [AC/DC; value]
Driver: [relay; triac; transistor; suppressor]
Cable: [length; shared multicore]
Head: [diameter; colour; metal or plastic bezel]
LED block: [threshold voltage; integral resistor]
If resistor: [value; power]
Protection: [IP; panel material]

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Indicator light sources

3 companies list this product among what they make. Company figures are quoted from each company's own website; every card states where the relationship came from.

CNC Electric

Manufacturing site to be confirmed for the order

Lists indicator lights for control panels on its own website; ask whether its LED heads have a voltage threshold.

Product scope checked 2026-10-13

Current product source ↗

Own-site product category: Indicator Lights · profile compiled by CNFX from public sources

View profile Send enquiry

CDOE Yueqing Dahe Electric Co., Ltd.

Manufacturing site to be confirmed for the order

Lists metal indicator lights, including an IP67 metal indicator light, on its own website; ask for off-state behaviour on AC.

Product scope checked 2026-10-13

Current product source ↗

Own-site product page: IP67 metal indicator light · profile compiled by CNFX from public sources

View profile Send enquiry

Filn

Manufacturing site to be confirmed for the order

Lists panel indicator lights on its own website; ask for off-state behaviour on AC.

Product scope checked 2026-10-13

Current product source ↗

Own-site product category: Indicator Lights · profile compiled by CNFX from public sources

View profile Send enquiry

Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.

Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review · Page last updated 13 October 2026

Buyer questions

Why does an LED pilot light glow when it should be off?

Schneider Electric attributes it to residual voltage or leakage current in the circuit. [1] [2]

How do I size a resistor to stop the glow?

Schneider suggests a temporary potentiometer, increased until the glow stops, then a fixed resistor of that value. [1]

Are there pilot lights that ignore low residual voltage?

Schneider points to its 22 mm range with a voltage threshold; ABB lists CL2 heads with 60 V anti-inductive voltage. [2] [3]

Does Schneider's 120 V LED block include a resistor?

No; Schneider says the 9001KP38LG contains only an LED block. [2]

Sources and what still needs a direct check

Sources checked 2026-10-13. Schneider Electric publishes support FAQs FA112098 and FAQ000256883 (read through a fetch tool; summarised, not quoted beyond the phrase marked); ABB publishes catalogue data for its CL2 compact pilot lights.

Schneider Electric USA — FAQ FA112098: residual voltage lighting LED modules in 30 mm Type K and SK pilot devices ↗ Manufacturer support note Return to text ↑
Schneider Electric — FAQ000256883: 9001KP38LG 120 V LED pilot light and leakage current ↗ Manufacturer support note Return to text ↑
ABB — CL2-623G compact pilot light, 1SFA619403R6232 ↗ Manufacturer catalogue entry Return to text ↑
ABB — CL2-623L compact pilot light data sheet, 1SFA619403R6234 (via Farnell) ↗ Manufacturer data sheet Return to text ↑

Still to check yourself

Name the driver per light.
State control voltage.
Ask for threshold voltage.
Size any resistor.
Test off-state at install.
Verify the legal supplier and factory.

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Indicator lights that stay dark when switched off (LED pilot lights on AC circuits, residual voltage and the voltage threshold)

Why an LED pilot light can glow when its circuit is off

An external resistor, or a head with a voltage threshold

LED indicator light details

Indicator light sources

Buyer questions

Sources and what still needs a direct check

Still to check yourself

Request manufacturing insight for Indicator Lights

Need to Manufacture Indicator Lights?