{"id":1335,"date":"2026-04-10T08:56:04","date_gmt":"2026-04-10T08:56:04","guid":{"rendered":"https:\/\/industrialsafetysensor.com\/?p=1335"},"modified":"2026-04-12T01:18:06","modified_gmt":"2026-04-12T01:18:06","slug":"type-4-safety-light-curtain-guide","status":"publish","type":"post","link":"https:\/\/industrialsafetysensor.com\/fr\/blog\/type-4-safety-light-curtain-guide\/","title":{"rendered":"Rideau lumineux de s\u00e9curit\u00e9 de type 4 : Guide de s\u00e9lection et de normes"},"content":{"rendered":"
\n

Type 4 Safety Light Curtain Guide: Standards, Selection, and Installation<\/strong><\/p>\n

<\/p>\n

\n

Quick Specs \u2014 Type 4 Safety Light Curtain<\/h3>\n\n\n\n\n\n\n\n\n\n
Safety Classification<\/td>\nType 4 \/ Category 4 (IEC 61496-1<\/a>) <\/td>\n<\/tr>\n
Safety Integrity<\/td>\nSIL3 (IEC 62061) \/ PLe (ISO 13849-1<\/a>) <\/td>\n<\/tr>\n
Detection Method<\/td>\nInfrared photoelectric beam array<\/td>\n<\/tr>\n
Resolution Options<\/td>\n14 mm (finger) \/ 30 mm (hand) \/ 90 mm (body)<\/td>\n<\/tr>\n
Response Time<\/td>\n5\u201320 ms (varies by protected height) <\/td>\n<\/tr>\n
Connector<\/td>\nM12, 5-pin or 8-pin<\/td>\n<\/tr>\n
Supply Voltage<\/td>\n24 VDC \u00b120%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

<\/p>\n

An operator is reaching into a point of operation at a press. The stop time is 200 ms. If the safety device doesn’t see his hand and trigger the machine to stop in just one scan cycle, the machine isn’t going to stop in time. That’s precisely the sort of scenario a type 4 safety light curtain<\/a> was built to prevent – which is why the difference between Type 2 and Type 4 is more significant than is revealed by most spec sheets.<\/p>\n

This article explains the engineering principles supporting a Type 4 classification, the criteria for selecting the resolution that fits the job, and the implementation factors that will equate to a compliant system that is actually safe. Every fact is referenced from either IEC\/ISO standards or published vendor data – not Marketing language.<\/p>\n

<\/p>\n

\n

In This Guide<\/h3>\n
    \n
  1. What Is a Type 4 Safety Light Curtain?<\/a><\/li>\n
  2. Type 2 vs Type 4: When Do You Actually Need Type 4?<\/a><\/li>\n
  3. How the Detection System Works<\/a><\/li>\n
  4. Safety Standards Behind Type 4 Classification<\/a><\/li>\n
  5. How to Select the Right Resolution: 14 mm, 30 mm, and 90 mm<\/a><\/li>\n
  6. Muting, Blanking, and Cascading Explained<\/a><\/li>\n
  7. Installation Mistakes That Compromise Safety<\/a><\/li>\n<\/ol>\n<\/div>\n

    <\/p>\n

    What Is a Type 4 Safety Light Curtain?<\/h2>\n

    \"What<\/p>\n

    An opto-electronic protective device (OEPD), also known as a safety light curtain, is an active optical intersection. It uses sets of photoelectric infrared beams to define an invisible detection field between a transmitter and a receiver. Break the light beams, and the sensor transmits a stop command to the machine’s safety controller within 20 ms or less.<\/p>\n

    What makes a safety light curtain “Type 4” is prescribed by IEC 61496-1, the international primary standard for electro-sensitive protective equipment (ESPE). The defining characteristic of type 4: in the event of any single internal fault, the device shall not cause the machine to become less safe. This requirement results in redundant internal supervision, dual-channel architecture, and self-diagnosis that monitors over 99% of known internal faults.<\/p>\n

    Thanks to this level of internal fault tolerance, Type 4 devices earn Category 4 (or PLe) under ISO 13849-1, and SIL3 under IEC 62061. These groups are mutually exclusive, based on different standards. However they all consistently arrive at this conclusion: Type 4 is the highest opto-electronic safety category.<\/p>\n

    \n
    \ud83d\udca1<\/span> Key Takeaway<\/strong><\/div>\n

    Internal fault behavior \u2014 not detection speed or resolution \u2014 is what separates Type 4 from Type 2 classification. A Type 4 device must maintain its protective function even when an internal component fails.<\/p>\n<\/div>\n

    <\/p>\n

    Type 2 vs Type 4: When Do You Actually Need Type 4?<\/h2>\n

    Comparing Type 2 and Type 4 is not about “good versus better.” Both types are safe when matched to the correct risk level through a proper risk assessment per ISO 12100<\/a>. What differs is how each type handles internal faults \u2014 and that difference determines which hazard levels each can protect against.<\/p>\n

    \n\n\n\n\n\n\n\n\n\n\n\n
    Feature<\/th>\nType 2<\/th>\nType 4<\/th>\n<\/tr>\n<\/thead>\n
    Internal test frequency<\/td>\nEvery 500 ms (periodic) <\/td>\nEvery scan cycle, <20 ms (continuous)<\/td>\n<\/tr>\n
    Fault response<\/td>\nDetected at next test cycle<\/td>\nDetected within one scan cycle<\/td>\n<\/tr>\n
    Redundancy<\/td>\nSingle-channel<\/td>\nDual-channel with cross-monitoring<\/td>\n<\/tr>\n
    External device monitoring (EDM)<\/td>\nOptional<\/td>\nMandatory<\/td>\n<\/tr>\n
    Self-diagnostic coverage<\/td>\n~60% of internal faults<\/td>\n>99% of internal faults <\/td>\n<\/tr>\n
    Safety rating<\/td>\nUp to Cat. 2 \/ PLc \/ SIL1<\/td>\nCat. 4 \/ PLe \/ SIL3<\/td>\n<\/tr>\n
    Typical risk level<\/td>\nLow to medium<\/td>\nMedium to high<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

    Type 2 safety light curtains sample their internal circuits every 500ms – such as the Schneider XUSL2E safety light curtain. Until a second self-test – between cycles – the interior circuit may be inoperative. Type 4 safety light curtains solve this problem by presenting a cascaded automatic cross-checking system which checks every element of the circuit on every scan cycle. When an internal fault occurs, the safety output switches to safe within the skip of the next available machine cycle.<\/p>\n

    \n
    \u26a0\ufe0f<\/span> Common Misconception<\/strong><\/div>\n

    “Type 2 is unsafe.” Wrong. For your ISO 12100 risk assessment, if your performance level ought to be PLd or PLe then type 2 is best. If a lower-risk task requires only 500ms safety light curtain self-testing cycles, then a higher-cost type 4 device will not improve your safety situation.<\/p>\n<\/div>\n

    Easy decision: perform the risk assessment first. If, as expected, the specified performance level turns out to be PLd or PLe, or the risk assessment indicates architecture must be Category 3 or 4, then type 4 is necessary. With a PL a through PLC specified and Category 1 or 2 architecture, type 2 can be justified. Our own electrically equivalent line of type 4 safety light curtains should be considered, if the risk assessment results call for them.<\/p>\n

    <\/p>\n

    How the Detection System Works<\/h2>\n

    \"What<\/p>\n

    A safety light curtain operates as paired units: an emitter (transmitter) and a receiver, mounted on opposite sides of the hazard zone. Modulated infrared beams project from the emitter across the protected field. On the receiving side, a matching array of photoelectric sensors detects each beam in sequence.<\/p>\n

    Scanning is sequential, not simultaneous. Beam 1 fires, the receiver confirms reception, then beam 2, and so on through the entire array. One complete sweep constitutes a single scan cycle, and the response time scales directly with beam count.<\/p>\n

    Response Time in Practice<\/h3>\n

    Response time measures how quickly the sensor signals the safety controller after a beam is interrupted. Typical figures from Keyence GL-R series datasheets:<\/p>\n

    \n
    \n
    6.9 ms<\/div>\n
    GL-R08L (240 mm height)<\/div>\n<\/div>\n
    \n
    15.7 ms<\/div>\n
    GL-R60H (1,800 mm height)<\/div>\n<\/div>\n
    \n
    19.2 ms<\/div>\n
    GL-R80H (2,400 mm height)<\/div>\n<\/div>\n<\/div>\n

    General formula: Tsensor<\/sub> = (Nbeams<\/sub> \u00d7 Tscan per beam<\/sub>) + Tprocessing<\/sub>. But sensor response time alone does not determine total stopping performance. What matters is:<\/p>\n

    Ttotal<\/sub> = Tsensor<\/sub> + Tinterface<\/sub> + Tmachine stopping<\/sub><\/p>\n

    All three values feed directly into the safety distance calculation covered in the installation section below.<\/p>\n

    Wiring and Connectivity<\/h3>\n

    Type 4 safety light curtains use M12 connectors \u2014 the standard industrial circular connector. A 5-pin M12 connector handles basic operation (power + safety outputs). An 8-pin M12 connector adds functionality for EDM feedback, muting input, and indicator signals. The 8-pin configuration is the standard choice for Type 4 installations where external device monitoring is mandatory.<\/p>\n

    \n
    \ud83d\udca1<\/span> Pro Tip<\/strong><\/div>\n

    Always verify the pin-out of a Type 4, before ordering to match your safety relays’ or safety controller inputs’. An incompatibility between the light curtain’s OSSD safety outputs and the safety device’s inputs is a common reason for late commissioning.<\/p>\n<\/div>\n

    <\/p>\n

    Safety Standards Behind Type 4 Classification<\/a><\/h2>\n

    \"Type<\/p>\n

    Type 4 safety light curtains sit at the intersection of multiple international standards. No single document covers everything \u2014 the classification, the control system design, and the physical installation each fall under separate standards that reference each other. Understanding how these standards interlock is a key attribute of competent machine guarding design.<\/p>\n

    \n\n\n\n\n\n\n\n\n\n\n
    Standard<\/th>\nScope<\/th>\nType 4 Relevance<\/th>\n<\/tr>\n<\/thead>\n
    IEC 61496-1<\/td>\nESPE general requirements<\/td>\nDefines Type 4: detect single fault, maintain safety function <\/td>\n<\/tr>\n
    IEC 61496-2<\/td>\nAOPD-specific requirements<\/td>\nSpecific to light curtains and light barriers<\/td>\n<\/tr>\n
    ISO 13849-1<\/td>\nSafety-related control system parts<\/td>\nPLe \u2014 highest performance level<\/td>\n<\/tr>\n
    IEC 62061<\/td>\nFunctional safety of control systems<\/td>\nSIL3 \u2014 safety integrity level 3<\/td>\n<\/tr>\n
    ISO 13855<\/a><\/td>\nPositioning of safeguards<\/td>\nSafety distance calculation formula (S = K\u00d7T + C) <\/td>\n<\/tr>\n
    OSHA 29 CFR 1910.212<\/a><\/td>\nUS machine guarding requirements<\/td>\nPoint-of-operation guarding mandate for US installations<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

    IEC 61496-1 (current edition: 2020) establishes both common requirements for all ESPE types and the specific criteria that separate Type 2 from Type 4. Part 2 (IEC 61496-2) narrows the focus to active opto-electronic protective devices \u2014 the category that includes safety light curtains, light barriers, and light grids.<\/p>\n

    For machines sold in the European Union, CE marking requires compliance with the Machinery Directive (2006\/42\/EC), which references ISO 13849-1 for the safety control system design. In the United States, OSHA 1910.212<\/a> mandates point-of-operation guarding but does not prescribe specific device types \u2014 mechanical guards, light curtains, or safety laser scanners<\/a> are all valid depending on the risk assessment.<\/p>\n

    \n

    \ud83d\udcd0 Engineering Note<\/strong><\/p>\n

    ISO 13849-1 and IEC 62061 are not competing standards \u2014 they are parallel paths to the same goal. ISO 13849-1 uses a parts-based reliability approach (Categories + PL), while IEC 62061 uses a probability-based approach (SIL). When you integrate a Type 4 safety light curtain into a control system, both standards converge at their highest levels: PLe and SIL3.<\/p>\n<\/div>\n

    <\/p>\n

    How to Select the Right Resolution: 14 mm, 30 mm, and 90 mm<\/a><\/h2>\n

    Resolution determines the smallest object a safety light curtain<\/a> can detect. It is the distance between the optical axes of adjacent beams, and it directly defines what body part the device can protect against. Getting the resolution wrong means the safety system cannot detect the hazard exposure it was installed to prevent.<\/p>\n

    Minimum detectable object size is calculated from the resolution using a formula defined in IEC 61496-2:<\/p>\n

    \n

    \ud83d\udcd0 Engineering Note<\/strong><\/p>\n

    Minimum Detectable Object = (Resolution \u00d7 2) \u2212 1<\/p>\n

    A 14mm resolution (14 2) 1 = 27mm (roughly 1 fingertip)<\/p>\n<\/div>\n

    \n\n\n\n\n\n\n\n
    Resolution<\/th>\nMin. Object Detected<\/th>\nProtection Type<\/th>\nCommon Applications<\/th>\n<\/tr>\n<\/thead>\n
    14 mm<\/td>\n27 mm (fingertip)<\/td>\nFinger detection<\/td>\nPress brakes, small-part insertion, die casting<\/td>\n<\/tr>\n
    30 mm<\/td>\n59 mm (hand)<\/td>\nHand detection<\/td>\nMachine loading, palletizing, injection molding<\/td>\n<\/tr>\n
    90 mm<\/td>\n179 mm (body\/leg)<\/td>\nBody detection<\/td>\nArea access control, robotic cell entry, conveyor zones<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

    Product Selection Checklist<\/h3>\n

    Ask yourself these five questions before selecting your resolution. Each one will eliminate some options:<\/p>\n