Pilot Light / Indicator Symbol
Definition: The Pilot Light / Indicator symbol represents a panel-mounted visual signalling device, designated H or HL in schematics, that illuminates to indicate the operational status — such as power on, fault, or run — of a machine or control circuit, with a positive (+) terminal and a negative (−) terminal, per IEC 60617 and ANSI/NEMA standards.
Also known as: indicator light, panel indicator, indicator lamp, signal light, status light, pilot lamp, control light, annunciator light.
What the Pilot Light / Indicator symbol means
The Pilot Light / Indicator symbol denotes a visual status-indication device mounted on a control panel, machine front plate, or distribution board. It illuminates when current flows through it, providing operators with real-time visual feedback on circuit state: whether a motor is running, a circuit is energised, a fault condition exists, or a process step has completed.
In control circuit schematics, the Pilot Light symbol appears in output circuits connected to PLC output modules, relay contacts, or timer contacts. The + (pos) terminal connects to the switched supply (typically 24 V DC or 120/240 V AC); the − (neg) terminal connects to common/neutral. Colour conventions communicate status: green = run/normal, red = fault/stop, amber/yellow = caution/pre-warning, white = power on, blue = specific function.
How to identify the Pilot Light / Indicator symbol
The Pilot Light / Indicator symbol is drawn as a circle (representing the lamp/LED body) with the reference designator H or HL inside or adjacent to it. Some representations add a stylised glow or radiation lines around the circle to indicate light emission. Two terminals, labelled + (pos) and − (neg), connect to the circuit. The IEC 60617 symbol for a general lamp or indicator uses a circle with an X inside (incandescent lamp) or a circle with a small light-burst symbol for LED indicators. The pilot light symbol is distinguished from a general lamp symbol by the 'H' designator and its placement in control circuits.
Function in a circuit
A Pilot Light / Indicator contains either an incandescent bulb, neon lamp, or LED element within a coloured lens housing. When voltage is applied between the + and − terminals, current flows through the light source, causing it to illuminate through the coloured lens. LED-type pilot lights typically include an integral current-limiting resistor and operate from 24 V DC or 120/240 V AC. Incandescent and neon types require external series resistors for AC operation. Some pilot lights include push-to-test functionality, where pressing the lens confirms the lamp is functional.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-08 covers pilot lights and indicating lamps under signalling and indicating devices. IEC 60947-5-1 governs control circuit devices and switching elements including pilot lights for industrial use. IEC 60073 specifies colour coding for indicator lights (green = safe/on, red = danger/stop, yellow = caution, blue = mandatory, white = neutral/power). The IEC symbol is a circle; for an LED indicator, a circle with LED symbol annotation. |
|---|---|
| ANSI/IEEE 315 | ANSI/NEMA ICS 5 covers control circuit and pilot devices including pilot lights for industrial machinery. ANSI/IEEE 315-1975 defines the indicator lamp symbol. NEMA pilot device standards specify push-to-test, voltage ratings (120 V, 240 V, 24 V), and colour lens options. The reference designator H (or HL) is per IEEE 200-1975. |
| Key difference | IEC 60073 and ANSI/NEMA ICS 5 align closely on colour coding conventions, with minor regional differences. The IEC schematic symbol uses a circle with an X for incandescent or a circle with LED annotation; ANSI/IEEE 315 uses a circle with a central dot or lines. Both use designator H or HL. The functional meaning is identical. |
Terminals / pins
| Pin | Name |
|---|---|
| pos | + |
| neg | - |
Typical values
Operating voltage: 24 V DC, 120 V AC, 240 V AC, or 6–48 V AC/DC (LED types); current: 15–40 mA (LED), 40–150 mA (incandescent); power: 0.5–6 W; lens colours: red, green, amber/yellow, white, blue; LED service life: 50,000–100,000 hours; incandescent bulb life: 2,000–5,000 hours.
Where the Pilot Light / Indicator symbol is used
- Motor control panels: green pilot light on the run contactor contact confirms motor is running; red light indicates stop or fault condition
- PLC output indicator circuits: LED pilot light connected to PLC digital output to visualise output state during commissioning and fault-finding
- Distribution and MCC panels: white or blue power-on indicators showing that a circuit or feeder is energised
- Process control systems: amber/yellow indicators for pre-alarm conditions such as high temperature or low level warnings
- Machine front panels: status indicators for cycle complete, door locked, fault active, or emergency stop activated states
- Building automation control panels: status lights for HVAC run/stop, fire alarm zones, and access control states
Example
In a three-phase motor starter schematic, a green Pilot Light (H1) is wired in parallel with the main contactor coil: its + (pos) terminal connects to the same node as the contactor coil positive supply, and its − (neg) terminal connects to common. When the START button is pressed and the contactor energises, H1 illuminates green through its 24 V DC circuit, confirming to the operator that the motor is running.
Key facts
- The Pilot Light / Indicator symbol (designator H or HL per IEEE 200-1975 and IEC 60750) represents a visual status-indication device with two terminals: + (pos) and − (neg).
- IEC 60073 specifies the internationally standardised colour code for pilot lights: green = safe/run, red = danger/stop, yellow = caution/warning, blue = mandatory action, white = power/neutral.
- LED pilot lights operate from 24 V DC (industrial standard) or 120/240 V AC with integral current-limiting resistors and have a service life of 50,000–100,000 hours.
- Incandescent and neon pilot lights require external series resistors to limit current at AC mains voltages; LED types usually include the resistor internally.
- Pilot lights appear in control circuit schematics (not power circuits) as output devices connected to relay contacts, PLC output modules, or contactor auxiliary contacts.
- Push-to-test pilot lights allow the lens to be pressed to briefly illuminate the LED/lamp, confirming the light source is functional without activating the controlled circuit.
- IEC 60947-5-1 governs pilot devices for industrial machinery including pilot lights rated for control circuit voltages up to 690 V AC.
- In schematic colour conventions, a pilot light drawn in red represents a fault or danger indication; a pilot light drawn in green represents a normal operating or run indication.
Diagrams that use this symbol
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- single phase contactor wiring diagram
Frequently asked questions
What does the pilot light symbol mean in a control circuit diagram?
The Pilot Light symbol (designator H or HL) in a control circuit diagram means that a visual status indicator is present at that node. When the circuit delivers voltage to the + terminal (relative to the − terminal), the indicator illuminates to show the operator that the connected circuit, machine, or process step is in the active state indicated by the lens colour (green = run, red = fault/stop, etc.).
What does the pilot light symbol look like?
The Pilot Light symbol is drawn as a circle (representing the lamp or LED body) with the designator H or HL inside or adjacent to it. Radiation lines or a small glow symbol around the circle indicate light emission. Two terminals, labelled + (pos) and − (neg), connect to the control circuit wiring. The IEC symbol for an incandescent pilot lamp adds an X inside the circle; LED types use a circle with an LED arrow annotation.
What do the different pilot light colours mean?
Per IEC 60073 and ANSI/NEMA ICS 5: green indicates safe/run (motor running, process normal); red indicates danger, stop, or fault; amber/yellow indicates a caution or pre-alarm warning; white indicates power on or a neutral status; blue indicates a mandatory condition or specific function. These colour conventions are internationally standardised and used in industrial control panels worldwide.
What are the terminals on a pilot light?
A Pilot Light has two terminals: + (pos, positive — connects to the switched supply voltage) and − (neg, negative — connects to the return/common/neutral). The positive terminal receives the circuit voltage (24 V DC, 120 V AC, or 240 V AC) when the indicator is energised; current flows through the LED or lamp element to the negative terminal, illuminating the device.
What is the difference between a pilot light and a general lamp symbol?
A pilot light (designator H) is a control circuit status indicator, typically rated at 24 V DC or 120/240 V AC, designed for panel mounting in a bezel with a coloured lens. A general lamp symbol (designator L or DS) represents a lighting luminaire providing illumination in a power circuit. The schematic symbols are similar (both use a circle), but the reference designators and circuit positions differ.
What standard defines pilot light symbols and colour coding?
Pilot light symbols are defined in IEC 60617-08 (indicating and signal devices) and ANSI/IEEE 315-1975. Colour coding is standardised in IEC 60073 (coding by colours and light-flashing) and ANSI/NEMA ICS 5 for industrial pilot devices. Component designator H (or HL) is defined in IEEE 200-1975 and IEC 60750.
Can a pilot light be connected directly to a PLC output?
A 24 V DC LED pilot light can be connected directly to a PLC sourcing (PNP) output if its current draw (typically 15–40 mA) is within the output's rated load current. For transistor outputs rated at 0.5 A, this is straightforward. For relay-output PLCs, the pilot light is wired between the relay contact and the supply return. High-voltage (120/240 V AC) pilot lights connect to relay contacts, not directly to solid-state PLC outputs.
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