Visual Signaling for Informed Management of Production Lines

By Etiido Uko, Lisa Eitel

Image of warning lights like these communicate the presence of a dangerous conditionFigure 1: The term visual management implies communications meant to prompt personnel action — which differs from other plant-floor visual communications merely meant to convey information. Warning lights like these communicate the presence of a dangerous condition. (Image source: Getty Images)

Image of visual management equipment in industrial applicationsFigure 2: Just like traffic lights to manage the behavior of drivers at street intersections, visual management equipment in industrial applications aims to spur personnel responses to set process requirements. (Image source: Banner Engineering)

Production lines for the processing, sorting, conveying, assembling, and packaging of goods typically incorporate equipment arrays that simultaneously execute interrelated, albeit separate, tasks. Such operations necessitate inclusion of components for safe and uninterrupted production. Here, visual signaling components are key. These quickly and effectively communicate machine data and other actionable information to plant personnel through lights or other visual (often color-coded) means — with little or no reliance on written instructions or text.

Also known in the context of industrial automation as visual control, visual management supports lean manufacturing and the efficiencies of IIoT lean-factory approaches. Such visual management can take the form of simple markings on factory floors, stickers and tags on communication billboards and workpiece batches, light towers (called andon lights) and other lighted electronics on control stations or machines, light strips on assembly-station part bins, and even ceiling-mounted flatscreens to communicate realtime conditions and instructions to plant personnel.

The primary aim of visual management in production lines is to ensure that all production and assembly processes occur as safely and efficiently as possible through timely and proactive communication of necessary operator or technician actions.

Visual management components

Visual management components in automated facilities serve three distinct functions — to convey actionable information on the condition of machines and processes in the production line, to give coded instructions to machine operators and other plant personnel, and to track production-line performance for better-informed enterprise-level decisions. Each of these functions is associated with overlapping lineups of dedicated visual management tools.

Visual alarms for plant personnel

Image of Floyd Bell LED-lighted piezo alarm for panel mounting and CAN networkingFigure 3: Visual alarms rely on sensors that detect when machine events occur — and are often accompanied by audible sirens. Shown here is an LED-lighted piezo alarm for panel mounting and CAN networking via the SAE J1939-15 protocol. The alarm’s sounds are configurable to communicate various alarm conditions. (Image source: Floyd Bell Inc.)

Visual alarms are LED lights, indicator lamps, and illuminated devices that optically draw the attention of machine operators and plant managers — usually as a dedicated warning of one very specific problem. Common causes of alarms include machine jams, overloading, overheating, leakages, pressure drops, electrical faults, impedance of safety functions, and fire. For especially dire situations, these visual alarms are accompanied by audible sirens.

For example, fire alarms integrate heat and smoke-particulate sensors as well as ruggedized electronics programmed to sound and flash signal outputs. In some cases, alarms also network into a high-level controller system that can command that a given alarm output its most conspicuous alerts should a series of ominous events occur.

Most industrial alarms only communicate that there’s an error — without any details about the error’s root cause or exact location. However, industrial-grade visual alarms are usually designed in a way that makes it intuitive to even the novice observer that there’s an issue — and the best can impart immediate understanding of the nature of the problem. For example, an alarm installed on a production line might flash or output some equivalent signal when its associated sensors detect a preprogrammed number of rejects. That in turn lets shift operators know that there’s an issue at some unspecified point on the conveyor or line. On other machinery, visual alarms are programmed to flash on and off according to timed patterns — much like nautical channel markers for waterway marine traffic — with coded meanings for each flashing pattern.

Machine-status indicators

Machine status indicators in industrial environments include the meters, gauges, and counters that many engineers conjure when they hear the word indicator. In fact, status indicators also include other automation components — including control-panel lights, light towers, and HMI features that signify the occurrence of a machine event or required personnel response.

In contrast with alarms that exclusively communicate the occurrence of hazardous, nonroutine, or other process-halting events, machine-status indicators are associated with actionable occurrences or metrics that are normal for a given operation. For example, they can display in real-time the amount of electricity being consumed or heat generated by a process running at some adjustable speed or torque on monitored equipment axis.

Andon lights and light towers

Image of Menics andon lightsFigure 4: Unlike alarms and indicators, andon lights are devices dedicated to a single machine condition. Andon light towers come in a variety of stack (light-color) counts and diameters. Industry-standard brackets and prewiring speed integration. (Image source: Menics)

Andon lights are a common visual-management component in today’s production facilities. They are tower lights with different vertically stacked colors. The term andon originates from a Japanese word for one type of stationary lantern — and its use in manufacturing originates from Toyota’s use of andons to refer to its early modern factories’ light-based problem-signaling systems.

Anodons are distinct from other visual-management components in that each one is associated with a given machine interlock, stop button, or operations-tracking device. The most distinct feature of andon systems is that they provide a means for personnel to stop the production line when a problem arises. The primary function of andon lights is to communicate to nearby personnel that there’s some problem on the line.

On an andon light tower, each color conveys an industry-standard message.

  • Green indicates that a production line is running and that there’s no problem detected.
  • Yellow indicates that the machine logic detects a problem … though production may still be running. An andon’s yellow light typically illuminates when there is an abnormality in the production line, such as excessive temperature, shortages, machine malfunction, or an abnormal number of rejects. Problems that trigger the yellow light are noncritical but may lead to more severe issues if they are not addressed.
  • Red indicates that production is stopped — often because a machine operator has tripped a machine interlock or pressed an e-stop button. When an andon system either detects or receives an alert of a critical problem requiring immediate attention, the andon tower’s red light turns on — and the andon system halts production. If production stops but not via the andon system (or stops for any reason undetected by the andon system) the red andon light will flash red. Production remains halted until the problem is fixed.

While the most common andon lights include stacks having red, yellow, and green lights, some only include red and green. Still, others include a white light and a blue light in the stack. The industry-standard meaning of an illuminated blue light on an andon tower is a request for assistance — whether for the delivery of materials replenishment, maintenance staff, or management. An illuminated white LED on an andon light tower on the other hand typically communicates a machine-specific condition related to a monitored productivity measure.

Simpler markings and plant signage

Image of standardized safety signageFigure 5: Safety signage employs iconography standardized by the National Electrical Manufacturers Association (NEMA), the American National Standards Institute in ANSI standard Z535, and the International Organization for Standardization in ISO standard 7010. (Image source: Getty Images)

Image of modest sign-based visual managementFigure 6: Modest sign-based visual management can ensure the safety of plant personnel. (Image source: Clarion Safety Systems)

Visual management in industrial settings needn’t be electronic. Modest (low-tech) markings, signs, and tags in and around work cells and machinery are essential elements of a well-designed lean manufacturing plant. Such signage serves to instruct and guide plant personnel. For example, floor markings can guide foot traffic along safe routes through manufacturing facilities. Elsewhere, icon-based labels can clearly indicate the correct positions of tools, binned parts for assembly, equipment axes, safety gates, and other objects.

The most important type of sign-based visual management is that related to personnel safety. Such signage is required by law anywhere there are hot surfaces, electrical hazards, wet floors, or risk of radiation exposure. Safety signs also alert workers as to the required personal protective equipment (PPE) for a particular work area … and when they’re approaching areas restricted to unauthorized personnel. Other examples of signs for visual management of production lines are laminated or hard plastic labels and tags describing steps to take in response to a given machine or plant condition or how to operate a simple device or piece of equipment.

Graphic boards and HMIs for KPIs

Image of digital IIoT connected screensFigure 7: Operations and KPI boards in factories increasingly take the form of digital IIoT connected screens to communicate individual work-cell and overall plant performance. (Image source: Getty Images)

Though beyond the scope of this article, it’s worth noting that recent years have seen increased reliance on HMIs to convey machine-level alerts and alarms. These HMI alerts are conspicuous on-screen signals that are often iconized to resemble physical dome and andon lights with which plant personnel are already familiar.

For communication of data related to plant and enterprise-level metrics (along with information on one or more production lines’ performance and current situation), plant-floor graphic boards are standard. These boards include non-electronic and electronic variations.

Non-electronic graphic boards are whiteboards and bulletin boards displaying hand-written information and computer printouts of production statistics related to work-cell throughput rates, parts finished and shipped, safety incidents, and more.

Simple electronic graphic boards take the form of LED scoreboards capable of displaying numbers on dot-matrix screens. In contrast, more sophisticated electronic graphic boards include digital flatscreens that network to machines and display equipment, factory-floor, and even enterprise-level data in real-time. In many cases, target throughput and other operational quantities are plotted against actual throughput and related quantities. Such values are called key performance indicators or KPIs — those indicators of operational rates and improvement measurements to inform business-level decision making. Besides KPIs, visual management boards often contain performance statistics related to work-station order fulfillment, number of parts produced, machine breakdowns, hours run without interruption, and number of days without an accident.


Visual management in the context of industrial automation includes systems and signaling components that communicate non-text instructions to plant personnel. In fact, components dedicated to visual-management functions either convey information on process and machine conditions or communicate actionable details about a production line’s performance and throughput. The inherently conspicuous nature of colorized, glowing, and blinking signs and signals is core to the success of visual management and the productivity benefits of an IIoT visual factory.

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

Etiido Uko

Etiido Uko is a mechanical engineer and technical writer covering industrial and commercial industries, with special expertise in DIN-rail industrial power supplies and other components, as well as control technologies used in both process automation and discrete automation.

Lisa Eitel

Lisa Eitel has worked in the motion industry since 2001. Her areas of focus include motors, drives, motion control, power transmission, linear motion, and sensing and feedback technologies. She has a B.S. in Mechanical Engineering and is an inductee of Tau Beta Pi engineering honor society; a member of the Society of Women Engineers; and a judge for the FIRST Robotics Buckeye Regionals. Besides her contributions, Lisa also leads the production of the quarterly motion issues of Design World.