Last revised: November 23, 2024

Reviewed by: Scott Orlosky, consulting engineer

Pilot lights also known as indicator lights are used to visually display the status of machines or instruments. Most indicators favor the use of LEDs or incandescent lamps.

Types of Lights

Pilot/indicator lights vary primarily by the type of lamp used.

• Incandescent lights emit light through a thin wire (filament) which becomes hot and glows when electricity flows through it. It can operate on either AC or DC circuits; however, these devices are relatively inefficient, generate heat, and have shorter operating life spans than LED lights.
• LED lights are semiconductor light sources that require DC to operate.  If a DC circuit is not available, an LED driver can be used to supply the appropriate DC voltage and current. They have the advantage of smaller size, longer lifetimes, and lower energy requirements than incandescent or fluorescent lights. Some LED lights are designed to display a range of colors to indicate a status change.
• Fluorescent lights utilize fluorescent bulbs which house electrodes at both ends of the tube and argon and mercury vapor throughout. A phosphor coating on the inside of the tube emits light through emission of ultraviolet light from excitation and stabilization of mercury atoms. Fluorescent bulbs tend to be more energy efficient and longer lasting than incandescent bulbs, but are less commonly used as indicators.
• Halogen lights utilize a tungsten filament, inert gas, and a small amount of a halogen to emit light. This combination allows for higher temperature filaments which can produce more light given the same energy (higher color temperature). This favors their use as daytime indicators and warning lights which require brighter light.

Product Specifications

Important specifications for these lights include electrical requirements such as voltage, size, and color. Based on the application, mounting style (panel, PC board) and terminal type (feed-through, wire leads, etc.) will also need to be considered.

To rate LEDs for use as pilot/indicator lights, manufacturers state the luminous intensity in candelas, which, for LEDs often is a function of the viewing angle.

Applications

These lights are used as malfunction lights in automatic equipment, lights for telephones, condition panels, dashboard lights for vehicles just as a few examples. They can also be built into switches to give a positive on or off indication.

Pilot Lights and Indicator Lights FAQs

What are the key differences between pilot lights and indicator lights in terms of functionality and application?

Here are some insights into the key differences between pilot lights and indicator lights in terms of functionality and application:

Functionality

Pilot Lights: These are a type of indicator light typically used to indicate the operational status of a device or system. An example is to provide indication status of a particular function; usually ON or OFF.

Indicator Lights: These are used more broadly to provide visual signals about the status of different parts of a system. They can indicate various conditions such as power status, fault conditions, or operational states. Indicator lights can be part of a larger control panel or system to provide comprehensive status information.

Applications

Both pilot lights and indicator lights are used in a variety of applications, including malfunction lights in automatic equipment, dashboard lights for vehicles. Status for power generation equipment. They can also be integrated into switches or push buttons.

What are the mounting styles for pilot lights and indicator lights?

Panel mounting style is very common, where the lights are installed directly onto a pre-drilled hole in the panel. Often it has a threaded body and is secured into the panel by screwing a thin threaded nut against the back of the panel. This style is often used in control panels and dashboards where the lights need to be visible and accessible from the front of the panel.

In PCB board mounting style, the lights are mounted onto a printed circuit board (PCB). This is typically used in applications where the lights are part of an electronic assembly and need to be integrated with other electronic components.

What are the electrical requirements for pilot lights and indicator lights?

Here are some insights into the electrical requirements for pilot lights and indicator lights:

Voltage

The voltage requirement is a critical specification for these types of lights. It determines the electrical compatibility of the light with the system it is integrated into. The voltage rating must match the system's power supply to ensure proper operation and avoid damage. If different types of lights are needed for functionality, then the electrical system may contain internal voltage supplies to accommodate the different voltages.

Size and Color

While not directly an electrical requirement, the size and color of the lights can influence their electrical characteristics, such as power consumption and visibility. These factors are important for ensuring that the lights meet the application's needs.

Terminal Type

The terminal type, such as feed-through or wire leads, is important for the electrical connection of the lights. This specification affects how the lights are integrated into the system and can impact the ease of installation and maintenance.

What are the luminous intensity ratings for LEDs used in pilot and indicator lights?

Luminous Intensity Measurement

Luminous intensity for LEDs is typically measured in candelas (cd) or millicandelas (mcd). One candela is equivalent to 1000 millicandelas. This is a measure of the brightness in a specific direction, and at a specific angle. Usually this would be the cone of illumination directly from the light source, toward the eye in the case of a panel-mounted light.

Function of Viewing Angle

The luminous intensity is a function of the viewing angle. This means that the intensity can vary depending on the angle at which the light is viewed. This is an important consideration especially when selecting LEDs for specific applications to ensure visibility from the desired angles.

Optical Power and Luminous Intensity

Optical power and luminous intensity are key performance specifications for LEDs. Optical power is the energy output of the LED, usually measured in milliwatts (mW), while luminous intensity is the amount of light an LED can emit, measured in millicandelas. These specifications become more critical in applications where higher light output is required.

What is the significance of luminous intensity in candelas for these lights?

Luminous intensity for these lights is related to their visibility and effectiveness in their applications. It is measured in candelas (cd) or millicandelas (mcd). This measurement indicates the amount of light emitted by the LED in a particular direction. This becomes especially important on a large panel, or a dashboard when the change in viewing angle from one side to another is significant. The perceived brightness can change based on the angle from which the light is viewed.

Luminous intensity is a critical performance specification for LEDs used in pilot and indicator lights. It helps determine the suitability of an LED for a particular application, especially in environments where higher light output is necessary.

In practical applications, such as malfunction indicators or dashboard lights, the luminous intensity ensures that the lights are bright enough to be noticed by users, thereby effectively communicating the status or condition they are meant to indicate.

What are the different terminal types available for these lights?

Feed-through Terminals

These terminals allow for the electrical connection to pass through the light fixture, making them suitable for applications where the light needs to be integrated into a continuous circuit.

Wire Leads

Wire leads are flexible wires that extend from the light fixture, allowing for easy connection to other components in the system. This type of terminal is often used when the light needs to be connected to a remote power source or control system.

Pilot Lights and Indicator Lights Media Gallery

References

GlobalSpec—Light Emitting Diodes