Install Easy-to-See Industrial Tower Lighting to Alert Nearby Operators of Machine Status Changes

By Bill Giovino

Contributed By Digi-Key's North American Editors

An industrial factory floor can be a busy, noisy, high traffic environment. The sound of manual and automated machines and vehicles can be confusing, which is why it’s imperative for an industrial facility to be set up so that critical machine status information is clearly visible across the facility. Many of the machines in an industrial automation facility need to alert nearby human operators of the present status of the machine. Failure to alert nearby operators of machine status can result in safety issues, reduced efficiency, or even equipment damage if operators are not made immediately aware of needed maintenance.

While there are many electronic and wireless methods of alerting operators, sometimes a simple visible alert is all that is needed. A panel indictor light is simple to implement but has the disadvantage of only alerting operators located right next to the machine. What is needed is a visible indicator that is unambiguous and can be clearly seen across the factory floor from many feet away.

This article explains how to implement stacked tower lighting in industrial automation facilities as a highly visible method of notifying nearby human operators of equipment status. The article examines the advantages of stacked tower lighting in a noisy, busy industrial automation facility and how it can be adapted to any industrial machine. It then looks at several examples of stacked tower lighting from Mallory Sonalert Products, Banner Engineering, and IndustrialeMart and how they can be easily adapted to interface to existing industrial equipment.

Equipment status notification in busy industrial facilities

Automated machines in an industrial environment require periodic monitoring and must provide an indication of status. It should be easy to determine if a machine is fully functional and operating within normal parameters. It is also important to determine if a machine needs maintenance and if that maintenance is preventive or immediate. Preventive maintenance is often determined by specialized sensors and can include predictive failures of equipment, refilling low coolant, or a bearing replacement. While not critical, preventive maintenance increases machine uptime, which saves costs by improving efficiency.

Basic machine status indicators include indication of normal operation, if the equipment needs service, or if the equipment is stopped due to malfunction or service. Both automated and non-automated industrial equipment have panel indicators to inform operators of the status of a machine. This can notify an operator that a specific action must be performed such as a changeover or a maintenance event. However, these panel indicators are usually limited to visibility by operators situated very close to the panel. What is needed is a method of quickly and easily notifying surrounding operators of machine status from a distance without the operators having to go to the machine or find a computer or mobile device.

Stacked tower lighting with high intensity lights provides a highly visible method of keeping everyone in the vicinity aware of machine status. Tower lighting offers a universal 360 degrees of visibility and can be seen from hundreds of feet away across a factory floor. It has the advantage of not only alerting surrounding operators of a machine’s service status but can also be a highly visible way of alerting others that maintenance has been delinquent if an alert light has been on for a prolonged period of time.

Stacked tower lights are also known as signal tower lights, stack lights, industrial signal lights, and on lights. They are designed to be easily mounted on top of industrial equipment and can extend to any height that is clearly visible to everyone in the surrounding area. Stacked tower lighting supports many different colors and can also provide audible alerts of status, providing an easy-to-see alert system for notifying everyone in a noisy, busy industrial environment of the present status of the machine. This can also be important if the machine is being controlled or configured remotely, when there is no local human operator to inform others of the machine operation being performed.

An example of a stacked tower light designed for industrial environments is the JT028-RYG-CSL green, yellow, red LED tower light from Mallory Sonalert Products (Figure 1). This is a pole mount stacked light that uses high intensity LEDs behind colored lenses to represent the machine status. It can also produce a piercing 2 kilohertz (kHz) steady state or pulsing tone (click to hear JT028-RYG-CSL sound) that projects a sound level of 80 to 85 decibels (dB) from one meter away.

Image of Mallory Sonalert Products JT028-RYG-CSL stacked tower lightFigure 1: The Mallory Sonalert Products JT028-RYG-CSL stacked tower light uses high intensity LEDs to produce green, yellow, and red alerts. It can also produce a 2 kHz tone that is either steady or pulsed. (Image source: Mallory Sonalert Products)

The entire unit only weighs 1.5 pounds (lb). Its power supply is a flexible 20 to 28 volts, either AC or DC. Each light has an individual power connection and can be controlled by connecting the power to a programmable logic controller (PLC) or the machine’s control computer.

Meaning of color indicator lights

The JT028-RYG-CSL stands 20 inches high and uses the standard steady or flashing green, yellow, and red lighting to indicate status. Usually these are completely automated and do not require operator intervention. Although there is no official standard, the accepted industry practice for these three lights are as follows:

  • Green: This is automatically indicated when the machine is on and operation is normal. Flashing green may also be automatically indicated when the machine is starting up and will be operational soon.
  • Yellow: While the machine is presently on and operational, this indicates an automated warning that the machine needs service or attention. It could be a high temperature warning or a request for maintenance. A flashing yellow could be an automated urgent request for service or that the machine is presently running a self-test.
  • Red: The machine is either stopped or is experiencing an emergency condition that could lead to an imminent shutdown. A flashing red typically means the machine has stopped operating and requires immediate attention by an operator for maintenance. Both steady and flashing red can be automatically generated when the machine shuts down on its own, or when an operator manually stops it.

It is up to the systems engineer configuring the equipment to determine the meaning for each light. For example, flashing yellow or flashing red could have a different meaning for each machine; however, it’s important to not deviate too far from accepted practice to avoid confusing new operators.

A more compact unit from Banner Engineering is the TL30BBGYRXAXC1 blue, green, yellow, and red tower light (Figure 2). This unit is 7.9 inches tall and operates over a wide range of 12 to 30 volts DC. The TL30BBGYRXAXC1 shows any inactive light on the tower as grey. This is useful for critical equipment as it eliminates any chance of a false indication, preventing operators from misinterpreting the status in a brightly lit industrial facility.

Image of Banner Engineering TL30BBGYRXAXC1 tower lightFigure 2: The Banner Engineering TL30BBGYRXAXC1 tower light has the standard red, yellow, and green lighting indicators as well as a blue light. As seen here, inactive lights show as grey to prevent false indications in a brightly lit environment. (Image source: Banner Engineering)

The TL30BBGYRXAXC1 also has a blue light. This is commonly used to indicate non-urgent machine service that is manually requested by an operator and is not related to an automated event. Flashing blue is machine specific but is often manually selected to indicate an urgent service or an operator’s request for a supervisor. When blue is used in the stack, yellow is then relegated only to requests for services that are automatically detected.

A practical use of the blue indicator light can be to notify operators that the machine is being configured remotely. If a remote operator is accessing the machine over the internal network and is changing the status of the machine, the blue light can be made to flash in a distinctive pattern to indicate a remote configuration in progress. This can be used simultaneously with the green light on to indicate whether the machine is being configured while operational, or simultaneously with the red light to indicate the machine is stopped due to remote configuration. This keeps the operators informed and prevents unnecessary troubleshooting.

The TL30BBGYRXAXC1 also supports an audible warbling alarm that is centered on 2.8 kHz with a ±500 Hz oscillation, with a maximum intensity of 90 dB at one meter. In an industrial automation facility that has both the warbling Banner Engineering TL30BBGYRXAXC1 and the steady tone of the Mallory Sonalert Products JT028-RYG-CSL, either machine alarm can be detected without confusion. This is important in busy facilities with many machines when the source of an audible alarm must be quickly determined.

Manual control of all indicator lights

For some equipment it is not possible to automate the machine status. This can be due to the use of older legacy equipment or fully mechanical equipment that does not use power. For these situations the IndustrialeMart ATEP-RYGBC pushbutton stack light can be applicable (Figure 3). There is a single pushbutton for each light on the tower and is powered by plugging it into a common 110 volts AC (VAC) outlet.

Image of IndustrialeMart ATEP-RYGBC pushbutton stack lightFigure 3: The IndustrialeMart ATEP-RYGBC pushbutton stack light is manually operated. It supports red, yellow, green, blue, and clear lights on the stack and is powered by plugging it into a 110 VAC outlet. (Image source: IndustrialeMart)

The ATEP-RYGBC is manually operated for machines that cannot support automated alerts. The machine operator must press each button to generate a corresponding light. Since yellow cannot be automatically generated, it is up to the systems engineer setting up the equipment to decide on the meaning for each light and to ensure the indicators for yellow and blue do not overlap. For example, the operator can press yellow only when machine maintenance is required, and blue only when a supervisor is requested, or if the operator needs to be temporarily relieved.

The ATEP-RYGBC also has a clear light at the base of the tower. Clear is machine specific and is up to the factory operators to decide what the clear light is to indicate.

For ease of use and to prevent operator confusion, it is useful to post a sign near the pushbutton panel that indicates what event each light button represents.


Tower lighting is a simple and practical method of alerting nearby operators of the status of a machine. It may not be as high tech as computer alerts or text messaging, but for a busy, high traffic industrial automation facility, it provides a highly visible alert system for notifying operators in the surrounding area of machine safety and status. As described, tower lighting can be quickly customized to a particular machine and is easy to understand as long as standard industry practices for the individual colors are followed. Proper use can increase productivity by improving machine uptime and reduce costs by increasing efficiency.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Bill Giovino

Bill Giovino is an Electronics Engineer with a BSEE from Syracuse University, and is one of the few people to successfully jump from design engineer, to field applications engineer, to technology marketing.

For over 25 years Bill has enjoyed promoting new technologies in front of technical and non-technical audiences alike for many companies including STMicroelectronics, Intel, and Maxim Integrated. While at STMicroelectronics, Bill helped spearhead the company’s early successes in the microcontroller industry. At Infineon Bill orchestrated the company’s first microcontroller design wins in U.S. automotive. As a marketing consultant for his company CPU Technologies, Bill has helped many companies turn underperforming products into success stories.

Bill was an early adopter of the Internet of Things, including putting the first full TCP/IP stack on a microcontroller. Bill is devoted to the message of “Sales Through Education” and the increasing importance of clear, well written communications in promoting products online. He is moderator of the popular LinkedIn Semiconductor Sales & Marketing Group and speaks B2E fluently.

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Digi-Key's North American Editors