What Is Pick-to-Light? How It Works, Types and Costs
Pick to light is a light-directed picking method: a small display at each storage location lights up to show the picker where to go and how many to take, and the picker presses a button on the display to confirm the pick. It replaces the paper list, the search along the shelf, and most of the errors that come with both.
This guide covers how a pick-to-light system works, what is in one, the types and the wired-versus-wireless choice, how many displays you need, where it pays off, what drives the cost, how it compares with RF scanning and voice, and how to roll it out one zone at a time. It is written by Voodoo Robotics, which makes wireless pick-to-light systems; where our own products come up, we say so.
In This Guide
What Is Pick-to-Light?
Pick-to-light (PTL) is a paperless order-picking system in which a light and display at each pick location tell a warehouse worker which location to pick from and how many units to take. The worker picks the items and presses the display's button to confirm; the system records the pick and lights the next location.
You will also see it called pick-by-light, light-directed picking, PTL and occasionally "pick2light." They are the same technology; the names differ by region and vendor (more in pick by light vs. pick to light). The reverse workflow, sorting items into orders instead of picking them from stock, is put-to-light, and its most common form is the put wall.
What the picker sees depends on the display. Classic modules show a lit button and a one- or two-digit quantity. Newer displays carry several lines of text, so they can also show the item, the location ID, the order or tote, an arrow toward the right bin, and a color that tells several pickers in the same aisle which lights are theirs.
Why it works: in manual picking, the slow and error-prone part is not taking the item but finding the right location and reading the right line on a list. A light at the location removes the search, and the button turns every pick into a confirmed transaction. That is where the accuracy and speed gains come from, and why pick-to-light is usually measured against mispicks and lines per hour rather than anything more exotic.
How a Pick-to-Light System Works
Every pick-to-light system, wired or wireless, runs the same loop: pick lines go out to the lights, the picker works from the lights, and confirmations come back. Step by step:
- 1
The order is released
Your WMS, ERP or order system decides what to pick and sends the pick lines (location, item, quantity) to the pick-to-light software, usually over an API.
- 2
The locations light up
The software turns each line into a command for the display at that location: light on, the quantity, often a color for the picker or order, and any extra text such as the tote number.
- 3
The picker follows the lights
There is no list to read. The lit displays show the route through the zone, and the quantity is waiting at each stop.
- 4
Pick and confirm
The picker takes the quantity shown and presses the button. Most systems also let the picker report a shortage instead of confirming, so an empty location becomes a replenishment task instead of a silent substitution.
- 5
The host system is updated
The confirmation goes back to the WMS in real time, inventory and order status update, and the next lines light up.
Discrete, batch and zone picking
In discrete picking the lights show one order at a time. In batch picking they show the total for several orders, and the items are separated afterwards, either at a put wall or directly into the totes on a pick-to-light cart. In zone pick-and-pass each zone lights only its own lines; the tote moves on by conveyor or cart, and a zone light tells the next picker there is work waiting.
Several pickers in one zone
Each picker or order gets a light color, so two or three people can work the same aisle without taking each other's lines. Displays with a text screen can add the picker's name or tote number for the same purpose.
Lights and scanners together
Lights find the location; scanners prove the item. Many operations scan the tote to start a batch, or scan the item where lot or serial numbers must be captured, and let the lights handle everything else. See barcode scanners with pick-to-light and RF scanners and pick-to-light for how the two divide the work.
What's in a Pick-to-Light System
Whatever the vendor, a pick-to-light system has the same layers. What differs is how the displays are powered and connected, and how the software reaches your WMS.
Displays (light modules)
A light, a confirm button and a display at each location: a numeric counter on classic systems, an alphanumeric or e-ink screen on newer ones. They mount on the shelf edge, rack beam, bin, cart or workstation.
Controllers or wireless routers
Wired systems run bus cable along the shelving to controllers that address each module. Wireless systems replace the cable with a radio router. Voodoo's Turbo II router reaches up to about 300 devices at 75–100 ft; production layouts plan roughly one per 100 devices with every display in range of two, mounted above the racks at about 8 ft on Power-over-Ethernet.
Pick-to-light software
Turns pick lines into light commands, tracks confirmations and shortages, manages colors, zones and timeouts, and reports battery or module health. It runs in the cloud or on a server on-site.
Integration with the host system
The link to your WMS, ERP or order system, through an API, middleware or a ready-made connector. This is usually the real project; see WMS pick-to-light integration below.
Power
Wired modules draw power from the bus. Wireless displays run on batteries; Voodoo's use two AAA cells and typically last a year or more, with battery levels visible in the dashboard.
Optional extras
Barcode scanners for item verification, zone and order-complete lights, put walls for sortation, and carts that carry displays to the pick face.
For integration, the WMS needs to send each pick line out and accept a confirmation back. Voodoo does this through a REST API and free connectors for Odoo (self-hosted), ShipStation, Extensiv, NetSuite and QuickBooks Online; the options are laid out in WMS pick-to-light integration. To see exactly what a picker sees on a Voodoo display, set the lines, quantity, arrow and color yourself in the device simulator.
Types of Pick-to-Light Systems
"Pick-to-light" covers a family of light-directed workflows. The hardware is often identical; what changes is where the displays sit and which direction the goods move.
By workflow
Shelf and flow-rack picking
The classic form: displays on every pick face of a zone of shelving or carton-flow rack, picking eaches into totes or cartons. Pick-to-light systems →
Put-to-light and put walls
The reverse workflow: after a batch pick, lights show which order or put location each item goes into. Put-to-light →
Pick-to-cart
Displays on the tote positions of a cart, so one picker batch-picks several orders and drops each item in the lit tote. Pick-to-cart →
Kitting and sequencing
Lights show the parts, and the order, for each kit or build at a workstation or line-side rack. Kitting solutions →
Pack-to-light
Lights at the pack station confirm the right items go into the right shipment before it is sealed. Pack-to-light →
Replenishment and putaway
The same displays light the location stock should go to, so restocking follows the same confirm-at-the-location discipline as picking. All use cases →
By display
- Light and button only. Shows where, not how many. Fine when the quantity is almost always one.
- Numeric display. The classic module: a quantity counter, a light and a confirm button, sometimes with plus/minus keys to report a short pick.
- Text or e-ink display. Several lines of text, so the display can show the item, location, order, tote or picker name, and an arrow toward a neighbouring bin. Voodoo's displays are five-line e-ink with an LED that supports thousands of colors.
By infrastructure
Fixed wired systems built into the shelving, wireless battery-powered displays on the same shelving, and mobile displays that ride on carts or move with a workstation. The next section compares the first two.
Wired vs. Wireless Pick-to-Light
For most of its history pick-to-light meant wired modules, and the cabling is a large part of why systems were expensive and slow to change. Battery-powered wireless displays remove the cable but add batteries to look after.
| Wired | Wireless (battery) | |
|---|---|---|
| Installation | Bus cable and controllers run along every shelf; usually electrical work and a planned shutdown of the zone | Displays mount to the shelf (magnets, on Voodoo's); routers mount above the racks |
| Power | Continuous, from the bus | Batteries, with levels to monitor |
| Moving a location or a whole zone | Re-cable | Move the display and update its location |
| Carts and mobile stations | Need on-board power or special cabling | The same display works on a cart |
| Up-front cost | Modules plus cabling, controllers and installation labor | Displays and routers; little installation labor |
| Ongoing upkeep | Cable and connector faults | Battery replacement |
| Best fit | Fixed, very high-volume lines that rarely change | Pilots, multi-zone sites, changing slotting, carts |
Wired still makes sense where power is already there and nothing will move: a pick module built into a conveyor or flow-rack system, for example. Everywhere else, wireless usually wins on installed cost and on what it costs to change your mind later. The longer argument, including latency and total cost of ownership, is in wired vs. wireless pick-to-light, and the case for going battery-powered is on wireless pick-to-light.
How Many Displays Does a Pick-to-Light System Need?
On a traditional system the answer is simple: one light per location. That makes the display count, and the price, track the location count, which is why pick-to-light was long reserved for a building's fastest movers.
Displays with a directional arrow change the arithmetic. One display can serve a single location or point at one of several neighbouring bins, so two warehouses with the same 400 locations can need 400 displays or 50. The trade-off is a fraction of a second spent reading the arrow, so fast movers usually stay at one per location while the long tail shares.
1 display per location
Large bins and fast movers, or anywhere a picker should not have to look twice
1 per 2 locations
Left/right arrow, common on wide shelving
1 per 4 locations
Four arrows; the usual starting point for dense bin shelving
1 per 6–8 locations
Small, slow-moving SKUs in tight rows
Demonstration with Odoo: one Voodoo wireless display serving 2, 4 or 8 neighbouring locations by pointing a directional arrow at the right bin, which cuts the number of displays a pick-to-light system needs.
Mixed ratios in one zone are normal. The device estimator on the pick-to-light pricing page turns a location count and a ratio into a display and router count.
Where Pick-to-Light Pays Off, and Where It Doesn't
Pick-to-light earns its keep where there are many picks per location and errors are expensive. It is a poor fit where picks are few, bulky or need item-level data capture on every unit.
Pays off
- Many order lines a day from a fixed set of pick faces: each-picking, small parts, spare parts
- Accuracy-sensitive work: e-commerce, retail store replenishment, medical and pharmacy supplies, customers who charge back for errors
- High staff turnover or seasonal peaks, where new pickers must be accurate on day one
- Batch picking with a sortation step: put walls or pick-to-light carts
- Kitting and assembly, where a missing part stops a line
Less suited
- Pallet and full-case picking from lift trucks; scanning or voice suits that better
- Huge SKU ranges where most locations are picked a few times a month, unless arrows bring the display count down far enough
- Workflows that must capture a serial or lot number on every unit; add a scanner rather than relying on lights alone
- Very low order volumes, where a paper list is still fast enough
The quickest way to find your candidate zone is to rank locations by lines picked: in most buildings a small share of locations carries most of the picks, and that is where the first lights go. Turnover matters too; shorter picker training is often the benefit operations notice first.
Benefits and Limitations of Pick-to-Light
Benefits
Fewer picking errors
Every pick is confirmed at the location it came from, so wrong-location picks and skipped lines largely disappear. Operations that confirm each pick at the location commonly run well under one error per thousand lines.
Less search time
The picker walks to the light instead of reading a list and scanning shelf labels; the quantity is already showing on arrival.
Faster training
Following lights takes minutes to learn, so temporary and seasonal staff pick accurately from their first shift.
Paperless and real-time
No printed lists. Supervisors see progress as it happens, and the WMS knows each line is done the moment the button is pressed.
Several pickers, one zone
Color-coding lets people share an aisle or a batch without crossing lines.
Limitations to plan for
Only as good as the location data
If the WMS has the wrong location for an item, the light points confidently at the wrong bin. Clean slotting data comes first.
Integration is the real project
Getting pick lines out of the WMS and confirmations back in is usually more work than mounting displays.
Hardware to look after
Cables and connectors on wired systems; batteries on wireless ones.
Confirming is not identifying
A button press confirms the location and quantity, not the item's barcode. Where the item itself must be verified, add a scan.
How Much Does Pick-to-Light Cost?
Published prices are rare in this market: most vendors quote per project, because the display count and the installation vary so much from one building to the next. What you can do is understand what moves the number.
Number of displays
Locations divided by how many each display covers. The biggest single driver.
Router or controller coverage
Wireless routers by device count and floor layout; wired controllers by module count and cable runs.
Installation
Cabling, controllers, electricians and downtime for wired systems; mounting and router placement for wireless.
Software licensing
A per-device subscription that grows with the system, or a one-time license.
Integration
A ready-made connector, a vendor-built integration, or your own developers using an API.
Rollout plan
One pilot zone, then phases, or a whole floor at once.
What Voodoo charges
- Starter Kit: $5,000. Ten wireless displays, a Turbo II router, an annually renewable cloud license (up to 50 devices), REST API integration support and onboarding. Every piece of hardware carries into production.
- Production: you buy the displays and routers outright and take a one-time perpetual license for your own Voodoo server, in the cloud or on-site. No per-device subscription.
- Larger systems are quoted per configuration, usually two or three configurations to compare, because the arrows ratio sets the device count.
Details on pick-to-light pricing; cost drivers and an ROI calculator in pick-to-light system cost and ROI.
Estimating payback
Add up the labor saved (search and walk time per line, times lines per year, times your loaded labor rate) and the errors avoided (errors per thousand lines before and after, times what an error really costs you), then compare the annual total with the one-time investment. The honest inputs come from your own floor, which is the strongest argument for piloting one zone and measuring it before buying the rest.
Pick-to-Light vs. Paper, RF Scanning and Voice Picking
Every picking method has to answer two questions for the picker: where do I go, and did I get it right? Pick-to-light answers the first one at the shelf instead of on a list, a screen or in an earpiece.
| Paper list | RF scanning | Voice picking | Pick-to-light | |
|---|---|---|---|---|
| How the picker finds the location | Reads the list, searches the shelf | Reads the screen, searches the shelf | Hears the location, searches the shelf | Walks to the lit display |
| How the pick is confirmed | A check mark, if anything | Scan of the location or item | Spoken check digit | Button press at the location (scan optional) |
| Hands and eyes | Hands hold the list | One hand holds the scanner | Hands and eyes free | Hands free; eyes on the light |
| Training | Low | Moderate | Moderate | Lowest: follow the light |
| Cost grows with | Nothing but labor | Number of pickers | Number of pickers | Number of locations served |
| Best for | Low volumes | Large SKU ranges, item and lot capture | Case picking over large areas | High-volume picking from fixed pick faces |
These are not either-or choices. Many buildings run lights in the fast-moving zone, scanners in reserve storage and voice for case picking, and decide zone by zone. The detailed comparisons: pick-to-light vs. voice picking, RF scanning with pick-to-light, and pick-to-light vs. put-to-light.
How to Implement Pick-to-Light in Six Steps
The pick-to-light projects that go well start small, measure, and only then spread. The ones that go badly start with the whole building and a guess.
- 1
Measure today
For a few weeks, record errors per thousand lines and lines per hour per picker in the zone you have in mind. Without a baseline you cannot prove the result. The mispicks guide shows how to count errors honestly.
- 2
Pick the zone
Start where the most lines and the most errors are, usually the fastest-moving locations. One zone, not the building.
- 3
Count locations and choose the ratio
Decide which locations get their own display and which share one through arrows. That gives the display and router count.
- 4
Check the location data
Every location ID in the WMS must match a physical location, and every item must be slotted where the WMS thinks it is. Fix this before the lights go up.
- 5
Choose the integration route
A ready-made connector if your platform has one, otherwise the vendor's API. Agree what happens on a short pick before go-live.
- 6
Pilot, compare, then scale
Install the pilot zone (a wireless pilot is typically a one-day install), run it for a few weeks, and compare against the baseline. Expand zone by zone; on Voodoo's system the pilot hardware carries into production.
For step one, how to measure your mispick rate. For steps three to six on Voodoo hardware, the wireless pick-to-light system page has the hardware, the integrations and the Starter Kit, and a real deployment is written up in the Nehemiah Manufacturing case study.
Pick-to-Light: Frequently Asked Questions
What does pick to light mean?
What is a pick-to-light system in a warehouse?
What does PTL stand for in a warehouse?
How much does a pick-to-light system cost?
Is pick-by-light the same as pick-to-light?
Does pick-to-light require wiring?
How does pick-to-light connect to a WMS?
How accurate is pick-to-light?
Can several pickers work in the same pick-to-light zone?
Try Pick-to-Light on One Zone First
Ten wireless displays, a router and a cloud license for $5,000. Light your busiest zone, measure it against your baseline, and keep every device when you scale.