What is a Light Curtain?
A light curtain (also known as a Safety light curtain) is a non-contact safety device that automatically switches off or stops a machine as soon as an object — typically a hand or arm — crosses a predefined protection field.
Light curtains are commonly used at robot cells, presses, packaging lines or access doors of hazardous Zones.
🧠 How does a Light Curtain work?
A light curtain consists of:
- A transmitter that emits a grid of infrared beams
- A receiver that detects these beams
- A Safety PLC or safety relay that initiates a safe stop immediately upon interruption
When one or more light beams are interrupted, the safety function is activated.
📐 Key specifications
| Property | Explanation |
|---|---|
| Resolution | Minimum detectable object size (e.g. 14 mm for fingers, 30 mm for a hand) |
| Protection height | Vertical coverage of the detection field |
| Range | Maximum detection range (e.g. 3 m, 6 m, 12 m) |
| Response time | Time between detection and machine stop |
| Safety level | PL or SIL depending on application (see ISO 13849-1) |
| OSSD outputs | Output for the safety circuit (e.g. 2x PNP redundant) |
🛡️ Safety and standards
| Standard | Relevance |
|---|---|
| ISO 13855 | Positioning relative to the hazard (minimum distance to the risk zone) |
| ISO 13849-1 | Performance requirements for safety functions (PL c, d or e) |
| IEC 61496 | Specific standard for electro-sensitive protective equipment |
| Machinery Directive | EU legal framework for the use of light curtains |
Light curtains are only sufficiently safe when correctly positioned, connected and validated.
🧩 Application examples
| Application | Purpose |
|---|---|
| Robot loading on a packaging line | Prevent operators from reaching into the gripper zone |
| Operator panel at a press | Prevent hands from entering the danger zone |
| Maintenance door of a CNC machine | Switch off motion when the door is opened |
| Conveyor with stop function | Automatic stop on obstacle detection |
✅ Best practices
- Choose the correct resolution based on the risk assessment (finger/hand/arm)
- Determine the minimum installation distance in accordance with ISO 13855
- Test periodically for proper operation and integrity (OSSD function)
- Protect against tampering (e.g. reflectors, bypass, covers)
- Combine with a safety relay or Safety PLC with fault detection
- Document in the safety dossier and link to CE marking
📌 In summary
Light curtains are essential components in safe industrial automation. They must be correctly selected, installed and verified in line with the relevant standards.