Pick-by-Light
Pick-by-light is a paperless, guided order-picking method in which lights at the shelf bin signal to the picker which storage location to pick from and how many units to take. Each pick is confirmed at the push of a button and reported back to the system in real time.
Pick-by-light is a paperless, guided order-picking method in which lights mounted directly on the shelf bin show which storage location to pick from. As soon as an order is started, a signal lamp lights up at each affected bin location, a display shows the quantity to be picked, and the picker confirms the pick at the push of a button. The method replaces the paper pick list with visual guidance right at the point of access and reports every pick back to the warehouse or ERP system instantly.
The big advantage lies in speed and accuracy: the picker neither has to read a list nor search for storage location numbers, but simply follows the light. Because both hands stay free and the search step is eliminated, pick-by-light achieves high picking rates at a low error rate. It is used above all at stationary picking stations with high throughput and a stable article range - for example in distribution centers, in spare-parts logistics, or in production supply.
At a glance
- Paperless order picking via light displays at the shelf bin
- Signal lamp shows the location, display shows the pick quantity
- Confirmation at the push of a button, instant feedback to the system
- Very high picking rate and low error rate
- Ideal with a stable article range and high throughput in a small area
How pick-by-light works
The method is based on bin displays (display modules) mounted at every storage location within a picking zone. Each module consists of a signal light, a small numeric display for the quantity, and a confirmation button, often supplemented by correction buttons. The modules are connected to a control bus and linked to the warehouse management system or the ERP. When a picking order is started, the controller activates exactly those bins from which items have to be picked for that order.
The process is simple and fast: the picker identifies the order container - usually via a barcode scan - upon which the light turns on at all affected bins. He walks the illuminated positions, takes the quantity shown on the display, places it in the container, and presses the confirmation button. The light goes out, the pick is posted immediately, and the order is complete once the last bin has been confirmed. This keeps the book inventory accurate in real time, and shortages become apparent right away.
Components of a pick-by-light system
A system typically comprises the bin displays with light, display, and button, a bus or network connection to the controller, a zone controller, and the software link to the WMS or ERP. Often an identification point is added at the zone entrance or exit, where the order container is registered. Large summary displays at the end of the zone indicate when a container is finished and can be passed on.
Benefits and limits of pick-by-light
The key benefit of pick-by-light is the combination of high speed and a low error rate. Because the visual guidance eliminates the search step and both hands stay free, the picking rate is well above that of paper-based picking. At the same time the picking error rate drops, because the system unambiguously specifies the location and the confirmation validates every pick. New employees are also quickly trained, because they only have to follow the light and do not need to memorize a warehouse layout.
These advantages come with clear limits. Pick-by-light requires a fixed installation of the displays at every location and is therefore capital-intensive and not very flexible: if the article range changes frequently or items often switch locations, cost-effectiveness declines. The method is therefore suited above all to zones with a stable, manageable article spectrum and high throughput. For widely distributed warehouses with a large, changing range, mobile methods such as pick-by-scan or pick-by-voice are usually more suitable.
Economically, pick-by-light pays off where the time saved per order and the avoided mis-picks exceed the investment in the hardware and its maintenance. Because the displays are tied to fixed locations, the zone should be carefully designed based on an ABC analysis before installation, so that the fast movers remain permanently in the equipped zone. A later redesign of the warehouse layout is more costly with fixed technology than with purely mobile methods.
Distinction: pick-by-light, pick-by-voice and pick-by-scan
All three are paperless picking methods, but they differ in the type of guidance. With pick-by-light, a fixed light display at the bin controls the pick - ideal for stationary picking stations with high throughput. Pick-by-voice guides the employee through the warehouse via a headset using voice instructions and is particularly suited to large-area warehouses with a changing range, since no fixed hardware is needed on the shelf.
Pick-by-scan (also pick-by-MDE) relies on a mobile terminal or a handheld scanner: the picker is guided via the display and confirms each pick by scanning the barcode of the article or storage location. It is the most flexible and most widely used method and can usually be run directly from the ERP. In practice the methods are often combined - for example pick-by-light in the fast-moving core zone and pick-by-scan in the rest of the warehouse.
Put-to-light as a related method
Closely related is put-to-light: here the light display is used not for picking but for sorting in. After a batch pick, the employee distributes the articles across the illuminated bins of the individual orders. Put-to-light is thus the typical second stage of a multi-stage batch picking process and uses the same display technology as pick-by-light.
Pick-by-light in the ERP system
The actual order logic sits in the ERP or the merchandise management system: a picking order is created from the customer order, the system reserves the quantities in inventory and assigns the storage locations. This data is handed over to the pick-by-light controller, which then activates the matching bins. Every confirmed pick is reported back and posts the inventory forward, so that availability and book inventory are correct at all times. For batch- or serial-number-managed articles, the picked batch is assigned to the order.
In practice a warehouse management system often sits between the ERP and the bin displays, handling the fine control of the zones and communication with the hardware, while the ERP runs the commercial processes. Smaller systems also connect pick-by-light controllers directly to the ERP via an interface or middleware. After picking is complete, the system hands the goods over to packing and shipping - in e-commerce often as an end-to-end pick-and-pack process through to the shipping label.
Example
Example: spare-parts warehouse of a machine builder
A mid-sized machine builder operates a spare-parts warehouse in which a few hundred fast-moving small parts account for the bulk of daily orders. These articles were consolidated into a compact shelving zone and equipped with pick-by-light modules. The picker registers the order container by scan, walks the illuminated bins, and confirms each pick at the push of a button.
The result after the switch: the picking rate in the core zone rose significantly, the error rate dropped to nearly zero, and new temporary staff were trained within a few minutes. For the remaining, broadly scattered range, mobile pick-by-scan from the ERP was retained. Every pick from the pick-by-light zone is posted immediately, so that planning works with an accurate real-time inventory.
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