Pick-by-light: how it works, trade-offs and WMS integration

Pick-by-light uses lights and displays to guide staff as they collect items. It can reduce search time and mistakes, but a light alone does not make a process reliable. The link between orders, stock and physical locations determines whether the instructions are correct. At Vlegel Technology in Genk, the Data, AI and Software Engineering team for factories and machine builders, we therefore look at the process first, then the technology.

How does pick-by-light work?

Each picking location has a light module and usually a display. The WMS, or another application that manages picking tasks, sends a task to the system. The correct location lights up and the display shows how many units to pick. The operator collects the items and confirms the action using a button or sensor. The confirmation is then processed and the next task can begin.

Pick-by-light is a form of operator guidance: software supports someone performing a physical task. The light shows where something needs to happen, but does not automatically check which item or how many units were actually picked. If you need that check, you need additional verification, such as a scan.

When does it fit, and when does it not?

Light-guided picking works best in clearly laid-out zones with fixed locations and frequent, repetitive picks. Staff spend less time looking at lists or handheld terminals. The simple instructions can also help new starters get up to speed. Results do depend on the layout, how easy the bins are to reach, and the quality of item and location data.

On the other side of the equation are hardware at each location, installation, maintenance and software integration. If your product range or warehouse layout changes regularly, scan-based picking may be more flexible. Multiple operators working in the same zone also need clearly assigned tasks. Colours or zones can help, but add complexity to the control logic. Define what an operator should do when a bin is empty, a display fails or the quantity is wrong.

WMS and ERP integration: agree the rules before the interfaces

The WMS usually manages picking tasks; without a WMS, an ERP can take on that role. The connection can use an API, middleware or an available connector. What the messages mean matters more than the interface you choose: which order, item, location and quantity belong to the task? When is a pick considered complete, and when is stock deducted?

Plan for failures too. A confirmation received twice must not deduct stock twice. After a connection drops, it must be clear which tasks are still open. Use identifiable task IDs, explicit statuses and a recovery procedure. Receiving a message is not the same as correctly completing a physical action.

If picking guidance works alongside a sorting machine or production line, OPC UA and MQTT can help connect the machines, depending on the available interfaces. A Unified Namespace (UNS) can make task statuses and machine events available under shared names. It does not replace the WMS: ownership of orders and stock must remain clear.

In practice: sometimes a screen is the better fit

Beumer commissioned us to develop software for a sorting machine at Royal Flora Holland. The software receives instructions specifying a trolley number and a position on that trolley for each box, and controls the sorting machine. Screens at the outlets use colour coding to show operators where to place the boxes. A separate scanner application lets a team leader check the intended position.

At a distribution centre, we worked on guidance for allocating boxes across three pallets. A barcode scanner determined the destination. We developed both a solution with signal lights and an on-screen display. The screen was chosen because it was considered more intuitive and ergonomic. Both examples involve visual operator guidance, not conventional pick-by-light at warehouse bins.

And the role of AI?

The fixed link between a picking task and a location does not need AI. AI could read recorded data to help investigate recurring discrepancies. We draw a clear line here: AI only reads, and a human decides. AI does not change stock, picking tasks or machine controls.

Want to weigh up whether pick-by-light, scanning or screen-based guidance suits your process? Let’s spend 15 minutes talking about the workstation, your existing machine and WMS connections, and the exceptions your staff have to handle today.