Introduction

Factories communicate through motion, sound, light, and rhythm. When a single station stumbles, the whole tempo breaks. Operators cannot babysit every HMI. Supervisors cannot hover over every cell. You need a signal you can see at twenty meters while a pallet jack rattles past and a compressor hums in the background. That is the role of a stack light.

The idea is simple. Encode states into color, flash, and sometimes tone. Keep meanings consistent from machine to machine. Train once. Operate faster forever. Yet complexity creeps in. Extra colors appear. New patterns arrive. A clever sequence that only two people understand sneaks into the standard. Confusion costs minutes, and minutes cost money. The goal of this article is to help you choose enough capability to solve real problems without turning a beacon into a puzzle.

As our colleague Neil Buzzard (global product marketing manager at c3controls) advises, “Keep your stacklights simple”. His advice is grounded in practical experience and human factors: roughly 8% of men are colorblind, so one in ten operators may find multiple-colored signals ineffective or even dangerous. Buzzard notes that the Americans with Disabilities Act (ADA) recognizes color blindness as a condition requiring accommodation, meaning overly complex light stacks can slow reaction times.

Lean manufacturing experts echo this insight – overloading a stacklight with information “leads to confusion” and should be avoided. In keeping with this philosophy, our paper emphasizes straightforward, consistent visual signaling schemes. By limiting stacklight colors and flash patterns to the essentials, we align with Buzzard’s principle to ensure clear, rapid operator response and compliance with industry best practices.

Sources: The principle above comes from Neil Buzzard in Control Design (“Stacklights show their true colors”)

The Family Tree: From Behavior to Build

Think of stack lights in three levels. Start with how the signal behaves. Then choose the family that fits the build, mount, and environment. Finally, pick a market variant that meets your budget and integration plan.

Level 1: Fundamental Signaling Methods

At the most basic level, stack lights communicate using a combination of visual and audible cues. The fundamental signaling methods include:

• Steady On: A continuous, unblinking light means the machine is in a stable, normal state. The steady glow of a segment is the anchor of any status system, nothing fancy, just an immediate indication of a normal (non-alarm) condition.
• Flashing: A blinking light means attention is required. Flashing is used to draw the eye, typically for warnings or faults. For instance, a slow flash can mean a low-priority warning or a pending changeover, whereas a rapid flash usually signals a critical fault or an emergency condition. The key is to keep the flash rates distinct and documented: if you use two different flash speeds (say, slow blink versus fast strobe), make sure everyone knows what each one means.
• Audible Alarm (Buzzer) with Visual: Adding sound can cut through background noise and alert people who might not be looking at the machine. A buzzer or horn integrated into the stack light is useful in a loud shop or when an operator might have their back turned. Use audible signals sparingly and only for conditions that truly warrant it – nobody appreciates a machine that cries wolf. Pick a reasonable volume (your stack light shouldn’t double as a fire alarm unless it’s truly an emergency) and reserve the loudest, most piercing tone for the few conditions that absolutely demand immediate human intervention.
• Rotating or Simulated Motion: Older beacon lights achieved a rotating effect with a motor and mirrors (like a police car light), and modern LED towers can simulate motion with chasing LED patterns. A rotating light or moving pattern is very demanding on the eyes – it will get attention, but it can also be overkill. Only use a rotating/moving signal where motion really adds value, such as a highly critical alarm in a noisy environment. In most cases, a flash will do the job without the extra cognitive load of interpreting motion.

Field Note: Most plants find that steady-on and flashing signals, plus an optional buzzer, cover 99% of their needs. If you think you need more than that (like multiple flash patterns, or a disco-ball tower with rotating lights), take a step back and confirm your training plan. You might also consider posting a one-page legend of the signals at the workcell. The simpler the signals, the quicker everyone reacts – clear signals beat clever signals every time.

Level 2: Categories by Design and Application

Once you know how you want the stack light to signal (steady vs. flashing, with or without sound, etc.), the next step is choosing the right design and configuration. Stack lights come in different technologies and physical builds, each suited for certain applications. We can categorize them in several ways:

A) Illumination Technology: What type of light source and optics does the stack light use? This affects brightness, power draw, and durability.

• LED: This is the modern default for stack lights. LED segments offer long life (often 50,000 hours or more), resist shock and vibration, turn on instantly, and are bright enough to be seen in daylight. LEDs also consume very little power relative to older lamps. They are suitable for almost every indoor application and even many outdoor ones.
• Incandescent: The old-school choice – basically a light bulb inside the tower. Incandescent stack lights are cheap to buy initially but costly to maintain. Bulbs burn out frequently, especially under continuous use, and they’re fragile in high-vibration settings (imagine a stack light on a punch press, rattling a filament to death). You’d typically only consider incandescent if you’re replacing a bulb in an existing older tower or in a temporary setup. Modern designs have mostly left these behind.
• Xenon Strobe: These use xenon flash tubes to produce an extremely bright, strobing flash. They are very hard to ignore (think of a camera flash or a strobe light). Xenon stack lights are useful outdoors or in very large indoor spaces like warehouses, where you need a brilliant flash to catch attention.
  Be mindful that xenon strobes have a brief recharge time between flashes and usually a higher power requirement. Also, strobe lights can be disruptive or unpleasant if overused (they can even trigger headaches or, in rare cases, seizures), so reserve them for urgent alerts like evacuation signals or critical faults.
• Fluorescent & Neon: These are rare in modern stack lights. Older designs might use neon indicators or small fluorescent lamps, but today, if you encounter these, it’s likely in a retrofit scenario. If you have a fluorescent/neon stack light that fails, it’s usually best to replace the whole thing with an LED-based unit, which will be brighter and more reliable.

B) Build and Configuration: How is the stack light physically put together, and can you modify it?

• Modular Towers: In a modular stack light, each segment (each color module, and possibly an audible module) is separate and stackable. You can add, remove, or swap modules to change the light’s configuration. This is great for OEMs (Original Equipment Manufacturers) who might need to customize lights for different machines, or for plants that reconfigure lines often.
  For example, you could start with a three-color tower and later add a fourth blue module if you decide to implement an Andon call system. The downside is you have more assembly, and if not assembled tightly, potential for water ingress – but generally the flexibility outweighs that for indoor use.
• Pre-Assembled Towers: These come as a fixed stack light under one part number (all the segments in one sealed unit). They are quick to install and often very rugged because the factory seals them up as one piece. You give up the flexibility of reconfiguring colors, but you gain simplicity. Use pre-assembled towers for common, repeat applications where you know the required colors and won’t need to change them. They’re also often rated for higher ingress protection because of the sealed design.
• Multi-Color Single Lens: Instead of separate colored modules stacked up, this design has one lens that can light up in different colors. Essentially, it’s a single “stack” segment that uses multi-color LEDs (RGB LEDs) to show any color you command. These look sleek and are compact – great where vertical space is limited or you want a low-profile indicator.
  The trade-off is that you generally can’t show multiple colors simultaneously (since there’s only one lens). They work best for showing mutually exclusive states (one state at a time). If you need to indicate two conditions at once (say machine running and low material), a single-lens solution wouldn’t handle that as intuitively as a multi-segment tower.
• Segment Size (Diameter): Stack lights come in various physical sizes – common diameters include 30mm, 50mm, 70mm, and even larger. Bigger diameters generally mean brighter light and visibility from farther away, because they can house larger bulbs/LEDs and larger lenses. You should pick the smallest size that still meets your visibility needs; a huge 70mm tower on a small benchtop machine might be overkill, whereas a 30mm mini-tower on a tall crane might be too dim to see from the ground. As a rule of thumb, use larger-diameter stack lights for long-distance viewing or brightly lit areas, and smaller ones for up-close equipment or tight spaces.

C) Mounting Options: Where and how will you mount the stack light? The mounting style ensures the light is in the line of sight and stays securely in place.

• Base Mount (Direct Mount): The stack light is mounted directly on a surface of the machine or enclosure, usually using a built-in base that screws down. This is good when the machine or panel is already at eye level or the equipment is tall enough that the light will be seen. It’s a sturdy mounting, but if the machine is low to the ground, a direct mount might put the light out of sight behind other obstacles.
• Pole Mount (Post Mount): Here, the stack light sits atop a pole (varying lengths available) that elevates it above the machine or nearby obstructions. Pole mounts are essential for low or mid-height equipment that might otherwise have the light blocked.
  For example, on a conveyor that’s only waist-high, you might use a 1-meter pole to raise the tower so people across the area can see it. Most pole-mounted lights route the wiring inside the pole for a clean look and protection.
• Wall or Side Mount: This means attaching the stack light to a vertical surface (like the side of a control cabinet, wall, or the side of a machine frame) using a bracket. It’s useful for situations like mounting an Andon light on a post or column in a facility, or on the side of a mezzanine. You might do this if there’s no flat top surface on the equipment, or if you want the light to project out for visibility in a certain direction.
• Panel Mount (Low Profile): Some indicator lights can be panel-mounted, meaning only a small dome or lens sticks out of a control panel or enclosure, rather than a tall tower.
  These are not “stacks” in the traditional sense (usually they’re single or multi-color indicators), but they serve a similar purpose for showing status. Use these where a tall stack might snag on something or be undesirable, but you still want an indicator on the panel door or operator station.
• Portable or Magnetic Mount: A few stack light models come with magnetic bases or portable stands. These are great for temporary setups – say a maintenance cart, a demo machine, or a reconfigurable cell in a lean manufacturing setup. You can pop the light on and off as needed. Just be sure the power source is convenient (some use a battery or a plug) and that the magnet is strong enough not to fall off if the surface gets bumped or vibrates.

D) Environment (Ingress and Hardening): The environment in which the stack light will operate determines how rugged it needs to be. Not all shop floors are clean and climate-controlled; some are wet, dusty, hot, or even hazardous.

• Indoor Industrial (General Purpose): Most standard stack lights are rated around IP54 to IP65, which means they can handle a bit of dust and the occasional water splash (like oil mist or light washdown). This is fine for typical indoor factories and assembly lines where conditions are relatively controlled. If your environment is just a typical manufacturing floor dust, maybe a splash or two of coolant, you’ll be well-served by a general industrial stack light in this category.
• Outdoor or Washdown: For outdoor use or environments that get hosed down regularly (food processing, beverage fillers, pharmaceuticals, and cleaning stations), you need a higher ingress protection. Look for IP66, IP67, or even IP69 K-rated stack lights, which are designed to resist water jets and heavy dust. Also consider UV-resistant lenses for outdoor sunlight exposure so the plastic doesn’t crack or fade. Sealing is critical here: in modular units, the seals between segments and around the wiring entry must be tight. A good washdown-rated tower will often have extra gaskets or o-rings available. In short, choose a stack light that won’t turn into an aquarium when it rains or when the cleaning crew does their job.
• Hazardous Location: These are special explosion-proof or intrinsically safe stack lights for areas with flammable gases, vapors, dust, or fibers (think chemical plants, oil refineries, grain silos). They have robust, heavy housings (often metal) and meet certifications for hazardous zones (like Class I Div 1/Div 2 or ATEX zones).
  They might have flame arrestors or other design features to ensure they don’t ignite the atmosphere. Such lights tend to be fewer colors (often just a couple of indicators) and may be larger and more expensive due to the engineering required for safety. Use them only if required – using a regular light in a paint booth or gas storage area is an accident waiting to happen.
• Hygienic or Corrosion-Resistant: In food, pharma, or outdoor marine environments, you may need stack lights made of stainless steel or special plastics. These will have smooth surfaces with no nooks (so bacteria can’t hide) and be able to withstand chemical washdowns or salty air. Look for IP69K ratings, stainless hardware, and mention of compliance with hygiene standards.
  These lights prioritize cleanability and corrosion resistance over raw brightness.
• High Temperature or Marine: For very hot areas (like near furnaces or baking ovens) or marine applications (exposed to saltwater spray), you need specialty stack lights. High-temp units use materials and electronics rated for heat – standard LEDs might dim or fail if baked beyond their limit.
  Marine units use anti-corrosion coatings and sealed enclosures to handle salt and moisture long-term. Always check the specified temperature range of a stack light if you plan to use it in an oven room or freezer (-20°C to 70°C, etc.), and ensure it matches your worst-case conditions.

E) Signal Characteristics: This category is about what the stack light can display or do, in terms of colors and display modes.

• Single-Color Indicator: This isn’t a “stack” in the multi-tier sense, but a single beacon light with one color. It’s dedicated to one status. For example, a lone red beacon might be used for an E-Stop status or a lockdown indicator. Single-color lights are unambiguous (it’s either off or that one color means something). Use them for singular purposes like a lone warning light on a gate, where you don’t need a whole stack.
• Multi-Color Stack (Multi-Segment): The classic stack light with, say, three to five separate color segments (red, amber, green, blue, white, etc.). Each segment has a dedicated color and usually a dedicated output from your controller to turn it on. This is the most common configuration because it can show multiple statuses (though typically you don’t light them all at once except perhaps during a power-on bulb test).
  The rule of thumb is that only one or two segments should be on at the same time during normal operation – if all five segments are lit, you’ve basically created a rainbow that no one can decipher. Multi-segment stacks are clear and direct as long as everyone knows the color code.
• Programmable RGB (Multi-color in one segment): Some advanced stack lights have LED segments that can produce various colors (thanks to RGB LEDs). For example, you might have three physical segments, but each segment can be any color you command via software or DIP switch. This provides flexibility – you could program a single segment to show green for one state, yellow for another, purple for yet another, etc.
  It’s useful in compact towers or where you want to standardize on one hardware unit but use it for many purposes. The caution: if you go this route, keep the scheme simple. People aren’t great at remembering that “turquoise means low air pressure” or “magenta means maintenance mode” unless you train and remind them constantly. RGB-capable lights are powerful, but that power should be used to simplify hardware (fewer part numbers), not to complicate the color code beyond recognition.
• Level or Bar Graph Mode: This is a special mode where multiple segments illuminate to show a level or percentage rather than discrete states. For example, if you have a five-segment tower, you might light up 3 segments to indicate 60% full on a tank, or use a growing bar to show progress through a batch process.
  This is a clever use for things like tanks, queues, or long cycle processes – the operator can see approximate progress from afar. Just keep the mapping straightforward (maybe each segment = 20%, or something intuitive). And be aware that using a stack light as a bar graph means you’re dedicating that light to that single analog-like purpose, which is fine as long as that info is useful to have at a glance.

F) Advanced Features: Modern stack lights can do more than just turn on and off; some come with built-in smart features that can integrate into advanced systems.

• Network Control (Industrial Communications): Instead of wiring each light to a separate output, some stack lights support protocols like IO-Link, Modbus, Ethernet/IP, or PROFINET. This means you can control the light’s behavior by sending it commands over a network, and even change its configuration in software.
  For instance, an IO-Link tower light might let you set flash rates, brightness, or colors via the control system without rewiring. This is great for standardized cells or when you want quick reconfiguration (e.g., product changeovers where the meaning of a light might change). The drawback is added complexity in setup and the need for a compatible master or PLC. But it can greatly simplify wiring (one cable for all five lights instead of five separate output wires).
• Wireless Status Transmission: Some kits offer wireless stack lights or add-on wireless modules. These are useful for mobile equipment (AGVs, carts) or retrofitting old machines where running new signal wire is expensive or impractical. The stack light might send its status to a central receiver or to the cloud.
  Just plan for how to power the light (battery vs. onboard power) and ensure the wireless signal is reliable in your environment (radio range, potential interference). Wireless stack lights can be a boon in large facilities for Andon systems, but have a contingency if the signal drops (most will fail-safe to a certain state or have a wired backup).
• Analytics and Data Logging: High-end stack lights or connected systems can log when and how often each segment was active. This can feed into OEE (Overall Equipment Effectiveness) calculations or downtime analysis. For example, you could track that Machine A was in red fault for 2 hours last week, versus 1 hour for Machine B, and dig into why. This is useful for continuous improvement – if your team actually uses the data. The presence of data logging is only an advantage if someone is looking at the reports; otherwise, it’s like having a car with a speedometer that no one ever checks.

Pitfall to Avoid: Buying a fancy networked or wireless-enabled stack light and then never configuring the advanced features. It sounds obvious, but it happens: a highly capable (and expensive) tower gets installed and ends up just showing a green light all the time because nobody set up the extra logic. Purchase the capabilities you will actually use, not just cool features that look good on a spec sheet. A simple $100 stack light that everyone understands will outperform a $1000 “smart” light that nobody ever fully implemented.

Level 3: Common Stack Light Configurations in the Wild

Having covered behavior and design options, let’s look at some typical stack light configurations you’ll see in real factories. Think of these as the greatest hits or the “market variants” that dominate shop floors:

• Three-Tier Modular LED Tower (with Optional Buzzer): This is the classic workhorse of the industry. Typically a red, amber, green stack (in that order top-to-bottom), often with a little piezo buzzer module either on top or built in. It runs on 24V DC in many cases, and has an IP54-IP65 rating for indoor use. You’ll find this on packaging lines, assembly machines, CNC equipment, you name it. The modular design lets the manufacturer or user add a blue or white segment if needed, or attach the buzzer. It’s not the fanciest, but it’s reliable and easily understood by everyone.
• Large-Diameter Programmable Tower: This is a bigger, brighter tower (maybe 70 mm diameter or more) where each segment can be programmed to different colors or functions. Plants might use a few of these models across all stations to simplify space, since one model can do it all via programming.
  These are great for large facilities or long viewing distances (like a warehouse or a big automotive plant) where you need that extra brightness and maybe a taller stack to be seen over equipment. The programmable nature means the same physical light can be green/yellow/red on one machine and blue/white/red on another, according to needs, though you’d still keep the overall color conventions consistent facility-wide.
• Compact Tri-Color Indicator (Single Lens or Small Stack): Picture a small device with three LEDs (often red, yellow, green) in one little dome or a very short stack. These are used on laboratory equipment, small bench-top machines, or inside test fixtures, places where a full-sized tower would be overkill or physically in the way.
  They give the basic stop/warning/go indication without a big footprint. They’re also common on material handling vehicles (like an AGV), where you want minimal hardware size. They might not be visible from across a factory, but they’re enough for the immediate area or for one operator working at that station.
• Explosion-Proof LED Stack Light: These look more like metal canisters with a few thick glass lenses and are built like a tank. They might have two or three segments (commonly red, amber, green) and are rated for Class I/II hazardous locations. You’ll see them in oil refineries, chemical plants, or grain processing facilities where any spark could cause a disaster. They often use high-intensity LEDs or bulbs to shine through those heavy enclosures. They’re also expensive compared to normal stack lights (think hundreds of dollars each), but they’re what you must use in those environments for safety and compliance.
• Wireless Andon Stack Kits: These are a bit newer on the scene – a kit might include a few stack lights with built-in wireless receivers and a pushbutton console or software that an operator can use to trigger them remotely. For example, an assembly cell operator hits a wireless button for “Need Parts”, and a blue light on a tower at their station starts flashing; simultaneously, a dashboard might update, or a supervisor carrying a tablet gets an alert.
  These kits are popular in retrofit scenarios, such as bringing lean manufacturing Andon systems into an older factory without running new wires. They’re also handy in facilities that rearrange frequently (you can just plug the lights in and rebind them to the central system as needed). Just ensure the wireless signal has range and reliability in your environment (and have a backup plan if interference is a concern).
• Integrated Sounder Towers: Many stack lights offer versions with an integrated multi-tone sounder at the top (or bottom). These can play different tones or melodies depending on which light is active. For instance, the green light might have no sound (machine running quietly), the yellow might pulse a gentle beep every few seconds, and the red might trigger a loud alarm tone.
  The idea is to provide an audible hierarchy matching the visual one. If you go this route, use the most piercing tone only for the highest urgency alerts. If every little jam makes a siren sound, people will tune it out or shut it off. Save the air-horn blast for the rare “line down” event, and use softer chimes or no sound at all for less critical states.

Standards and Consistency: Speaking the Same Signal Language

Color meanings only help if everyone uses the same dictionary. In other words, the value of a red or green light is greatly diminished if each machine or each team interprets it differently.

Fortunately, most plants follow a pretty common pattern for stacking light colors, because it shortens training and prevents mistakes. In fact, there are industry standards (like NFPA 79 in North America and IEC 60204 internationally) that guide color usage and even the physical order of stack light segments. The details can vary by region or company, but the core ideas are similar. Here are the conventional meanings for the standard colors:

• Red: Stop or danger. This indicates a critical condition – the machine has stopped due to a fault or safety issue, and immediate attention is required. Red means do not ignore me.
• Amber (Yellow): Caution or attention needed. An amber light usually means the process is deviating from normal or about to require intervention. For example, an amber steady light might mean the machine is starved of material or blocked by a downstream backup – a condition that is not an emergency, but someone should address it before it becomes a bigger problem.
• Green: Normal operation. Green is the status we all want to see – it tells you the machine is running and everything is okay. A green light means production is flowing, no interventions needed. Operators often use green as the default state: machine running = green on. If the stack light is entirely off, some use that to mean the machine is off or idle, but many prefer a white or other neutral color for “idle/ready” and reserve green purely for “actively running.”
• Blue: Often means a call for service or assistance. Blue isn’t in every stack light, but many plants use blue to signal that an operator or machine is requesting help – for example, a machine finished its cycle and needs an operator to unload it, or an operator pressed a help button for a supervisor or material handler.
• White: Often means ready or a neutral status. White can indicate that the machine has power and is ready to run, but is not actually running yet. For instance, you might have white on when a machine is on standby.

No matter which colors you use, keep the order of the stack light segments consistent across all machines. A common approach is red at the top (most critical at the highest point), then amber, then green, then any additional colors like blue or white towards the bottom. The idea is that even if someone can’t distinguish colors (e.g., due to color blindness or just viewing angle), they know the top light being on is bad, and the bottom might be something less urgent.

Decide also whether flashing versus steady is a separate meaning. Some standards recommend that flashing means a more urgent version of the same color (e.g., red flashing = severe fault, red steady = minor fault).

Remember that not everyone perceives color the same way. A sizeable portion of the population has some form of color vision deficiency (around 8% of males, for instance). For these folks, the position of the light and the pattern (steady vs flashing) become even more important. That’s why putting red at the top is helpful – a color-blind person can learn the top light means trouble without needing to see red.

Similarly, using sound in parallel can assist if someone doesn’t notice the color or is in doubt. And as mentioned, a simple text legend or icon on the machine or in standard operating procedures can reinforce the color codes for new hires or contractors.

Field Note: Beware of the “rainbow creep.” When a vendor proposes adding purple, cyan, or magenta lights because “hey, we have LEDs that can do 16 million colors!”, it’s usually not a great idea. Novel colors slow recognition and often don’t add meaningful information.

Applications that benefit right away

Manufacturing and assembly

• Machine status at a distance. A supervisor can scan fifteen meters in both directions and know where to go first.
• Andon calls. Operators trigger a service or quality light without leaving the station. Response time drops, flow improves.
• Changeover and warm-up. Use white for “ready” and keep green reserved for “running” so green always equals product flowing.

Process and utilities

• Batch state. Green for run, blue for operator step needed, amber if limits approach, red for interlock.
• Tank levels. A bar mode gives a truthful glance from across the bay. One caveat. Keep thresholds and colors consistent to avoid mixed interpretation.
• Central plant equipment. Boilers, compressors, and chillers benefit from large diameter towers at doorways so status is visible before someone enters a noisy room.

Warehousing and material handling

• Conveyor junctions and merges. A red flashing tower at a merge gets attention faster than a line on a screen.
• Loading bays. Clear red and green signals reduce miscommunication between dock staff and drivers.
• AGVs and AMRs. Small towers provide a moving billboard for the state. Pair with audible chirps in mixed traffic zones.

Clean industries and labs

• Autoclaves and sterilizers. Use gentle tones and clear green or white for complete and safe to open.
• Pharma washdown. Smooth housings and high ingress ratings are more important than raw brightness.

Public, broadcast, and education

• Studios and classrooms. Red for recording live. No tone needed. Quiet rules apply.
• Training rigs. Towers help learners see cause and effect without deep HMI knowledge.

Advantages that show up on the scorecard

• Immediate recognition. Color and flash patterns hit peripheral vision faster than text on glass. You do not need to wake a screen to know a station needs help.
• Shorter time to respond. When you can see the exact machine with a fault, you do not wander. Mean time to repair drops. Throughput rises.
• Better operator span of control. One person can oversee several semi-autonomous stations with confidence. You can run higher machine-to-operator ratios without blind spots.
• Safer interventions. A red flashing tower near a guarded area warns people who arrive mid-cycle. The cue is present even when ear protection mutes tones.
• Lower training load. New hires learn one light code and use it everywhere. Cross-training gets simpler. Contractors make fewer mistakes.
• Data you can use. If your towers are networked or monitored, you can correlate red time, root causes, and shifts. That feeds continuous improvement rather than anecdotes.
• Good cost profile. LED towers draw little power, survive vibration, and pay back quickly by avoiding a single long stoppage.

Selection criteria that prevent surprises

The selection of a stack light is a crucial part of designing an industrial automation system. A well-chosen stack light provides clear, immediate feedback on a machine's status, improving safety and efficiency. To prevent surprises and ensure the light works as intended, here are the key selection criteria, broken down into simple terms.

1. Environment and Durability

This is the most important factor. The stack light must be able to withstand its operating environment.

• Ingress Protection (IP) Rating: This rating tells you how well the light is sealed against dust and water. A basic IP rating is fine for a clean, dry indoor environment. However, if the light will be exposed to dust, occasional splashes, or a washdown, you'll need a higher IP rating (e.g., IP65 or IP67).
• Material: For outdoor use or areas with UV exposure, choose a light made with UV-safe materials to prevent the plastic from becoming brittle and discolored.
• Hazardous Areas: In environments with flammable gases or dust, you must use a stack light with a certified enclosure that is rated for that specific hazardous location.
• Vibration and Temperature: Check the product's specifications to ensure it can handle the temperature and vibration levels of your machine.

2. Visibility and Distance

The light needs to be seen and understood from where people are working.

• Size: The diameter of the light (e.g., 50mm, 70mm, 100mm) should be chosen based on the distance from which it needs to be seen. A larger diameter is better for bright, large factory floors.
• Brightness: Look for a light with high intensity (often measured in millicandelas or lumens) to ensure it's visible in a well-lit area.
• Pattern: Decide whether you need a continuous light, a flashing light, a strobe, or a rotating light. Flashing and strobing lights are more attention-grabbing and are typically used for warning or fault conditions.

3. Number of States and Colors

Keep the signaling simple and easy to understand.

• Number of Segments: A typical stack light has three to five colored segments. Each color should represent a distinct machine status (e.g., Red = Fault, Yellow = Warning, Green = Running).
• Avoid Over-Complication: If you find yourself needing more than five segments, you might be trying to communicate too much information through the light. It's often better to use a simple legend on the stack light and provide more detailed information on an HMI screen.

4. Illumination and Audible Layer

The type of light and sound you choose adds to the effectiveness of the signal.

• Light Source: LEDs are the standard choice due to their long life, energy efficiency, and low maintenance.
• Flashing Rate: Use different flash rates to indicate urgency. A slow flash might be a low-priority warning, while a rapid flash signals an urgent fault.
• Audible Alarm (Buzzer/Horn): Consider if a sound is needed, especially in loud environments. Many stack lights can be equipped with a buzzer or horn. Look for models with adjustable volume and tone to match the noise level of the environment and to differentiate between different alarms.

5. Power and Control

Make sure the stack light is compatible with your electrical system and control logic.

• Voltage: The light's voltage (e.g., 24V AC/DC, 120V AC, 240V AC) must match your plant's standard.
• Control Method: Confirm your controller has enough outputs to control each light segment separately. Alternatively, you may choose a networked stack light that communicates via an industrial protocol like IO-Link, which simplifies wiring.

6. Mounting and Assembly

Proper physical installation ensures the light functions correctly and safely.

• Mounting Type: Common options include pole mount, direct mount, or wall mount. Choose one that places the light in a clear line of sight for all personnel.
• Modularity vs. Simplicity: Modular stack lights allow you to add or change segments as needed. This is great for flexibility. Pre-assembled, sealed units are simpler and more durable for fixed applications, as they have fewer places for leaks or loose connections.
• Cable Routing: Plan for tidy and protected cable routing, such as internal pole wiring, to prevent damage and maintain a clean appearance.

7. Compliance and Site Standards

Consistency is key to clear communication and safety.

• Standardize Meanings: While there is no single international standard for all stack light colors, it is crucial to establish a consistent meaning for each color within your facility. For example, "Red always means Stop/Fault," "Yellow always means Warning," and so on.
• Create a Legend: Write a one-page legend defining the meaning of each color and flash pattern, and post it near the machine and in the machine's manual. This ensures that every worker understands the signals and can respond appropriately.

Example specification in one sentence:

A three-segment LED tower at 24 volts direct current, with green steady for run, amber steady for attention, red fast flash for fault, optional buzzer at 85 decibels for red only, pole mounted to one point eight meters above floor, ingress rating sufficient for washdown in the aisle adjacent to the filler.

Implementation playbook

Decide on the code before buying parts. Agree on color meanings, flash plan, and any tones. Get operations, maintenance, and safety in the same room for fifteen minutes. That short meeting saves months of drift.

Prototype one cell. Mount the tower where people naturally look. Test from common approach angles. Stand where a team lead stands. Adjust height or position until the signal is obvious on first glance.

Publish and label. Print the legend in large type. Put it near the station and in the quick reference pocket. Add the legend to the lockout sheet so it is always nearby.

Train by walking the line. A five-minute walk with new staff where you point to each color in context has more value than a slide deck. People remember sights from their own aisle.

Use data if you have it. If your towers connect to a network, review the week’s red time in the daily standup. If they do not, at least log the longest stops. Signals only matter if someone listens.

Audit quarterly. Check lenses for haze. Wipe them during planned maintenance. Confirm flash rates did not get changed in a software update. Make sure new machines match the standard. Drift is natural. Correct it before it becomes the new normal.

Common pitfalls to avoid

• Adding colors because the hardware allows it, rather than because the process needs it.
• Making green flash look exciting. Green should be calm.
• Setting the buzzer to scream for minor stops. People will disable it.
• Mounting behind a guard or banner where the bottom segments vanish at a distance.
• Letting each integrator choose their own order. Inconsistency multiplies error.

Conclusion

Stack lights have stuck around in modern industry for a simple reason: they align with how humans naturally perceive information. We react quickly to colors and flashing lights; it’s an almost hard-wired response. A well-placed green or red beacon tells a story in half a second, from across the aisle, without a single word being spoken. In factories that want to be safer and more efficient, that kind of clarity is gold.

The key to reaping the benefits is to keep the stack light system simple, consistent, and focused on what truly matters. Pick a small set of clear states (don’t try to signal the meaning of life with one tower). Use standard colors and mounting so that anyone walking in can decode it instantly. Mount the lights where eyes naturally land – they can’t do their job if they’re hidden or too low. Document the meanings and train your people in the actual work environment. If you can log or monitor the signals, use that information to continually improve your processes (and not just gather dust in a database).

In the end, the best stack light is not the fanciest one with every feature under the sun. It’s the one that every person on your team can read without thinking twice. When a new operator says, “I like these lights, they always let me know what’s going on,” you’ve done it right. Keep your stack lights simple, and they will serve as the heartbeat of your visual management system for years to come.

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