{"id":2561,"date":"2026-05-07T02:28:07","date_gmt":"2026-05-07T02:28:07","guid":{"rendered":"https:\/\/industrialsafetysensor.com\/?p=2561"},"modified":"2026-05-07T02:28:07","modified_gmt":"2026-05-07T02:28:07","slug":"type-2-vs-type-4-safety-light-curtain","status":"publish","type":"post","link":"https:\/\/industrialsafetysensor.com\/es\/blog\/type-2-vs-type-4-safety-light-curtain\/","title":{"rendered":"Cortina de luz de seguridad tipo 2 frente a tipo 4: Gu\u00eda de decisi\u00f3n SIL (2026)"},"content":{"rendered":"
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Making a choice between a Type 2 or Type 4 safety light curtain isn’t often much of a free choice – the answer is dictated by the risk graph in ISO 13849-1, the IEC 61496-1 ESPE standard, and the machine-type specific Type-C standard for your application. This article unpacks how those standards align, explains why Type 4 hardware is around 15-30% pricier than Type 2 hardware but often cheaper over five years, and how to run the four-step selector that our application engineers run prospects through before providing a quote for an ENT Series light curtain. We end with the changes in regulation due to EU Machinery Regulation (EU) 2023\/1230 coming 20 January 2027.<\/p>\n

Reviewed against IEC 61496-1, ISO 13849-1:2023, ISO 13855:2024, IEC 62061, OSHA 29 CFR 1910.217, and EU Regulation 2023\/1230(accessed 2026-05-06).<\/p>\n

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Quick Specs \u2014 Type 2 vs Type 4 at a glance<\/h3>\n\n\n\n\n\n\n\n\n\n\n
Reference standard<\/td>\nIEC 61496-1 + IEC 61496-2 (ESPE \/ AOPDs)<\/td>\n<\/tr>\n
Achievable safety level<\/td>\nType 2 \u2192 SIL CL 1 \/ PL c \u00a0\u00b7\u00a0 Type 4 \u2192 SIL CL 3 \/ PL e<\/td>\n<\/tr>\n
PFHd window (per hour)<\/td>\nPL c: 1\u00d710-6<\/sup> \u2013 3\u00d710-6<\/sup> \u00a0\u00b7\u00a0 PL e: 1\u00d710-8<\/sup> \u2013 1\u00d710-7<\/sup><\/td>\n<\/tr>\n
Self-diagnostics<\/td>\nType 2: periodic self-test \u00a0\u00b7\u00a0 Type 4: continuous dual-channel cross-check<\/td>\n<\/tr>\n
Effective Aperture Angle<\/td>\nType 2: \u00b15\u00b0 \u00a0\u00b7\u00a0 Type 4: \u00b12.5\u00b0<\/td>\n<\/tr>\n
Resolution coverage<\/td>\nType 2: hand 30 mm + body 40-70 mm \u00a0\u00b7\u00a0 Type 4: finger 14 mm + hand 30 mm + body 40 mm<\/td>\n<\/tr>\n
Hardware price index<\/td>\nType 4 typically 15-30% above Type 2 for comparable height (industry guides) <\/td>\n<\/tr>\n
Where it usually fits<\/td>\nType 2: low-risk auxiliary equipment, perimeter assist \u00a0\u00b7\u00a0 Type 4: power presses, robot cells, finger-detection at point of operation<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

QJKH ENT Series specs referenced where applicable (response time 14 ms, IP65, protective height 160-1827 mm).<\/p>\n<\/div>\n

1. At a Glance \u2014 Type 2 vs Type 4 Side-by-Side<\/h2>\n

\"1.<\/p>\n

If time’s short, then here’s the comparison that most procurement decisions are based on. Application-specific selective choice of a safety device is ultimately limited by your machine’s Type-C standard \u2014 but this nine-row table explains why Type 4 dominates point-of-operation safety guarding while Type 2 light curtains offer cost savings on lower-risk perimeters. The difference between Type 2 and Type 4 reduces to two numbers: the achievable level of protection (PL c versus PL e) and the self-test cadence.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Dimension<\/th>\nType 2 Safety Light Curtain<\/th>\nType 4 Safety Light Curtain<\/th>\n<\/tr>\n<\/thead>\n
Reference clauses<\/td>\nIEC 61496-1 + -2, Type 2 requirements<\/td>\nIEC 61496-1 + -2, Type 4 requirements<\/td>\n<\/tr>\n
SIL CL (IEC 62061)<\/td>\nSIL CL 1<\/td>\nSIL CL 3<\/td>\n<\/tr>\n
PL (ISO 13849-1)<\/td>\nPL c<\/td>\nPL e<\/td>\n<\/tr>\n
Internal architecture<\/td>\nSingle-channel CPU + periodic self-test<\/td>\nDual-channel CPU + continuous cross-check<\/td>\n<\/tr>\n
Single-fault tolerance<\/td>\nDetects between scheduled tests<\/td>\nDetects continuously, fail-safe in milliseconds<\/td>\n<\/tr>\n
Effective Aperture Angle<\/td>\n\u00b15\u00b0 (higher optical short-circuit risk near reflective surfaces)<\/td>\n\u00b12.5\u00b0 (tightened against optical short)<\/td>\n<\/tr>\n
Detection resolution<\/td>\nHand 30 mm + body \u226540 mm<\/td>\nFinger 14 mm + hand 30 mm + body 40 mm<\/td>\n<\/tr>\n
Hardware cost premium<\/td>\nBaseline<\/td>\n+15-30% over Type 2 of comparable height <\/td>\n<\/tr>\n
Typical role in safety architecture<\/td>\nSecondary or perimeter access on low-risk machinery<\/td>\nPrimary point-of-operation guarding on high-risk machinery<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Type 3 (PL d \/ SIL CL 2) is recognised by IEC 61496-1\/-2:2020 in a third middle category. Type 3 falls under IEC 61496-3, which covers active opto-electronic protective devices responding to diffuse reflection (AOPDDR) \u2014 more often safety laser scanners<\/a> than photoelectric light curtains. For curtains, it remains a one-way choice between the faster, more reliable and more expensive Type 4 and the lower cost Type 2.<\/p>\n

2. How IEC 61496 Defines Type 2 and Type 4<\/h2>\n

\"2.<\/p>\n

IEC 61496-1 is the main standard for electro-sensitive protective equipment (ESPE) \u2014 the broad class that every type of light curtain, light grid, and laser scanner falls under. It is the standard through which two principles determine Type classification: the measures taken to ensure a device fails safely if it detects a single-fault, and the frequency of the device’s self-tests. According to IEC 61496-1, the applicant defines the hazardous state and the factory standards for function and electrical implementation; the device is just one element of the overall safety function defined by the relevant machinery safety standards.<\/p>\n

IEC 61496 itself is made up of four parts – taking all four into account stops even application-wide comparisons from sounding simplified marketing brochures. For completeness, the safety light grid family is also part of IEC 61496-2 – like light curtains, they use a hand- or finger-resolution grid of multiple closely spaced infrared transmitter and receiver pairs, and sense a break in the beam pattern. However, they only have 2-4 light beams widely spaced apart rather than a dense grid:<\/p>\n

\n\n\n\n\n\n\n\n\n
IEC 61496 Part<\/th>\nScope<\/th>\nTypical device<\/th>\n<\/tr>\n<\/thead>\n
Part 1<\/td>\nGeneral requirements for all ESPE<\/td>\nApplies to every Type<\/td>\n<\/tr>\n
Part 2<\/td>\nActive opto-electronic protective devices (AOPDs) \u2014 emitter+receiver beam arrays<\/td>\nPhotoelectric safety light curtains (Type 2 + Type 4)<\/td>\n<\/tr>\n
Part 3<\/td>\nAOPDs responsive to diffuse reflection (AOPDDR) \u2014 time-of-flight zone scanning<\/td>\nSafety laser scanners (Type 3)<\/td>\n<\/tr>\n
Part 4<\/td>\nVision-based protective devices (VBPDs) \u2014 added in 2021<\/td>\nCamera-based machine vision safety<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Within Part 2, Type 2 is designed to detect a single fault at the next scheduled self test (every 100-500 ms in modern setups), while Type 4 will leave the device in a safe state if a single fault occurs and not wait for the next test cycle. That difference necessitates the dual processor dual channel OSSD output architecture seen specified on every Type 4 datasheet; including QJKH’s ENT Series.<\/p>\n

OSHA accepts IEC 61496 parts 1 and 2 (adopted in the United States as ANSI\/UL 61496) as the standard-equivalence validation for safety light curtains used on regulated machinery, according to OSHA’s Machine Guarding eTool<\/a>. Each of the standards’ certified curtains must be identified with their standard part number, the certification number, and the third party body that completed the type examination.<\/p>\n

3. SIL & PL \u2014 What Type 2 (SIL CL 1 \/ PL c) and Type 4 (SIL CL 3 \/ PL e) Actually Mean<\/h2>\n

\"3.<\/p>\n

Most articles break down this layer into “SIL 2 vs SIL 3,” and that is the number one culprit for confusing a buyer. Type 2 light curtains are rated SIL CL 1 per IEC 62061- not SIL 2- and Type 4 light curtains are rated SIL CL 3. Why “CL” is important: it stands for claim limit, and it limits the maximum SIL a sub-system within an architecture specified by IEC 62061 can achieve. Bare “SIL” labels (without CL) are IEC 61508 \/ IEC 61511 function-level purity for the process industries, and “SIL CL” belongs to sub-systems of machinery. Interchanging the two is how purchasing consistently predicts wrong.<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Performance Level (ISO 13849-1)<\/th>\nSIL CL (IEC 62061)<\/th>\nPFHd window (per hour)<\/th>\nLight curtain Type that meets it<\/th>\n<\/tr>\n<\/thead>\n
PL a<\/td>\n\u2014<\/td>\n\u226510-5<\/sup> to <10-4<\/sup><\/td>\nBelow ESPE territory<\/td>\n<\/tr>\n
PL b<\/td>\nSIL CL 1<\/td>\n\u22653\u00d710-6<\/sup> to <10-5<\/sup><\/td>\nType 2 (lower bound)<\/td>\n<\/tr>\n
PL c<\/td>\nSIL CL 1<\/td>\n\u226510-6<\/sup> to <3\u00d710-6<\/sup><\/td>\nType 2 typical<\/strong><\/td>\n<\/tr>\n
PL d<\/td>\nSIL CL 2<\/td>\n\u226510-7<\/sup> to <10-6<\/sup><\/td>\nType 3 laser scanners (per IEC 61496-3)<\/td>\n<\/tr>\n
PL e<\/td>\nSIL CL 3<\/td>\n\u226510-8<\/sup> to <10-7<\/sup><\/td>\nType 4 mandated for finger detection<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Translate the math: a PL e component – Type 4 in our world – averages up to one dangerous failure in 10 to 100 million operating hours. This means a properly maintained ENT Series Type 4 curtain experiences about one expected dangerous failure over an entire century of single-shift operation. PL c is one full order of magnitude less demanding. Whether that difference is relevant depends only upon the severity of the consequences of failure, which is what the next H2 explains.<\/p>\n

For a side-by-side comparison in your own architecture our PL\/SIL category mapper<\/a> converts risk-graph output to the appropriate sub-system SIL CL using ISO 13849-1:2023 Annex A and IEC 62061 conversion tables.<\/p>\n

4. Internal Architecture \u2014 Single CPU vs Dual CPU Self-Diagnostics<\/h2>\n

\"4.<\/p>\n

The difference in architecture is what physically gains the SIL CL difference. Type 2 curtains use a single processing channel with a self-test sequence at boot and regular intervals – vendors usually specify a 100-500 ms test period. If a beam circuit fails in between tests the curtain may continue to produce seemingly normal OSSD output until the next test detects the error. For applications where this reduction in risk is acceptable the delay is tolerable.<\/p>\n

Type 4 curtains have sister emitter, receiver, and processing pathways, each of which use a separate processor to compare the images across each beam frame. Dual-channel OSSD outputs are wired so that any individual component failure causes both channels to fall to the safe state within the curtain’s declared response time \u2014 typically under 14 ms in current designs including the QJKH ENT Series. Extra Device Monitoring (EDM) provides further assurance by resetting the contactor feedback after every safety stop- a welded contactor is detected before the next start.<\/p>\n

“A key component of a safety light curtain is the output signal switching devices (OSSDs), which are typically solid-state transistor components used to switch a safety relay to control the machinery causing the dangerous motion.”<\/p>\n

\u2014 Derek Charge, Global Product Manager \u2014 Safety, Sensing & Industrial Components, Rockwell Automation (via A3 Industry Insights)<\/cite><\/p><\/blockquote>\n

Diagnostic Coverage (DC) and Mean Time to Dangerous Failure (MTTFD) are the two ISO 13849-1 numbers that quantify the architectural gap. Type 2 designs typically deliver DC in the 60-90% band (“low” to “medium”), while Type 4 designs deliver DC \u226599% (“high”). MTTFD on a Type 4 ENT Series circuit sits in the ISO 13849-1 “high” category at 30-100 years<\/code> per channel \u2014 the standard caps reportable MTTFD at 100 years even when component analysis suggests longer \u2014 which is what makes the PFHd math close out at PL e for the protected hazardous area within the broader machine safety system.<\/p>\n

5. Risk Assessment \u2014 When Does the Standard Push You to Type 4?<\/h2>\n

\"5.<\/p>\n

ISO 13849-1:2023 itself states without qualification that it does not specify the Performance Level needed for any specific application, that the decision is based on the risk assessment for the specific machine, and that “[i]f a particular application requires, ISO 13849-1:2023 specifies the application-specific Type-C standard (for example: ISO 14118 for unexpected start-up; ISO 12100 for general safety design principles).” What ISO 13849-1:2023 does specify is a risk-graph matrix Annex A that takes three axes and outputs a required PL.<\/p>\n

Q: What does safety category 4 mean when referring to a light curtain?<\/h3>\n

“Category 4” is an integration standard describing the architecture of the safety-related portions of the control system, according to ISO 13849-1:2023, not the light curtain alone. A Type 4 light curtain is intended for use in a Category 4 \/ PL e arrangement: two OSSD outputs lead to dual safety-relay channels, and at the plug\/end-to-end, the entire chain sensor-to-actuator is rated to the PFHd of the weakest link. When you select a Type 4 curtain, you haven’t necessarily selected a Category 4 arrangement or vice-versa; relays, voltaging, wiring topology, and EDM feedback must match.<\/p>\n

Within the Annex A matrix you address three questions in order: severity (S), frequency\/duration of exposure (F), and possibility of avoiding injury (P). Output from each combination (a-e) is a required PL; that PL may be used as your guidance for itepick light curtain or may be supplanted by application-specific Type-C standards.<\/p>\n

“Light curtains, typically, are a Category 4, SIL 3, PLe safety element, used where a door or other barrier is not preferred for the application’s access needs, but they also can be accommodated within the stop-time limits of the hazard they are protecting.”<\/p>\n

\u2014 Steve Lange, Technical Application Engineer, Schmersal Canada (via A3 Industry Insights, 2024)<\/cite><\/p><\/blockquote>\n

The seemingly-driven risk table turns out to have answerable questions, but it is in fact a framework for agency assessment. Two engineers reviewing the same light curtain hazard can arrive at different scores, and ISO 13849-1:2023 clarifies that possibility of post-avoidance assessments may vary. A pragmatica assessment of a QJKH: if actual worst-case injury results in an irreversible loss (S2), exposure is more than a negligible chance (F2), and the operator cannot protect themselves in time (P2), the method makes the common-sense decision for you: PL e, and the light curtain equipment selection becomes Type 4-if architecture; Category 4.<\/p>\n

6. Application Map \u2014 Where Each Type Fits<\/h2>\n

\"6.<\/p>\n

The rows below layout wherein each Type in the categories is implemented today in applications through mechanical, automation, and intralogistics design. Use of “PL e” refers to the risk graph more or less consistently, results in PL e for the application; alternative approaches (two-hand controls, pullback tension devices, fixed guards) are often regulator-accepted replacements.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n
Application<\/th>\nRisk graph commonly maps to<\/th>\nRecommended Type<\/th>\n<\/tr>\n<\/thead>\n
Mechanical power press, 14 mm finger detection (29 CFR 1910.217 PSDI mode)<\/td>\nPL e<\/td>\nType 4<\/td>\n<\/tr>\n
Hydraulic press brake (ANSI B11.3-2022 \u2014 multiple safeguarding paths permitted)<\/td>\nPL d\u2013e<\/td>\nType 4 light curtain or two-hand \/ pullback \/ restraint<\/td>\n<\/tr>\n
Robot cell perimeter access, ISO 10218<\/td>\nPL d\u2013e<\/td>\nType 4 (perimeter mode)<\/td>\n<\/tr>\n
Collaborative robot finger zone, ISO\/TS 15066<\/td>\nPL e<\/td>\nType 4 + force-limited control<\/td>\n<\/tr>\n
Packaging line muting (product pass-through)<\/td>\nPL d<\/td>\nType 4 with muting safety light curtain<\/a> arms<\/td>\n<\/tr>\n
Palletising cell, EN 415 family<\/td>\nPL d<\/td>\nType 2 or Type 4 depending on stop-time and reach analysis<\/td>\n<\/tr>\n
AGV \/ AMR gateway access, EN ISO 3691-4<\/td>\nPL d<\/td>\nType 3 laser scanner primary; Type 2 curtain as gate-assist<\/td>\n<\/tr>\n
Light curtains are suitable for conveyor pinch-point body protection at low energy<\/td>\nPL b\u2013c<\/td>\nType 2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

The OSHA Machine Guarding eTool for power press brakes<\/a> recognises four equivalent safeguarding methods \u2014 presence sensing devices (light curtains), two-hand controls, pullback devices, and restraint devices \u2014 and lets the employer’s risk assessment decide which is most workable. That is why the press-brake row above offers more than one path. ANSI B11.3-2022 governs the device-level requirements once a method is chosen.<\/p>\n

7. Performance Specs Compared \u2014 Response Time, MTTFD, DC, Resolution<\/h2>\n

\"7.<\/p>\n

Once we have defined the Type, a set of 7 specs determine its actual compatibility to the machine. An example for the short ENT Series is shown on the right column.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Spec<\/th>\nType 2 typical<\/th>\nType 4 typical<\/th>\nQJKH ENT Series <\/th>\n<\/tr>\n<\/thead>\n
Response time<\/td>\n15-30 ms<\/td>\n8-20 ms<\/td>\n\u226414 ms<\/td>\n<\/tr>\n
MTTFD per channel (ISO 13849-1 categories)<\/td>\n10-30 years (medium) typical<\/td>\n30-100 years (high) \u2014 capped at 100<\/td>\n30-100 years (high)<\/td>\n<\/tr>\n
Diagnostic Coverage (DC)<\/td>\n60-90%<\/td>\n\u226599%<\/td>\n\u226599%<\/td>\n<\/tr>\n
Detection resolution<\/td>\n30 mm hand \/ 40-70 mm body<\/td>\n14 mm finger \/ 30 mm hand \/ 40 mm body<\/td>\n14 \/ 30 \/ 40 mm selectable<\/td>\n<\/tr>\n
Effective Aperture Angle<\/td>\n\u00b15\u00b0<\/td>\n\u00b12.5\u00b0<\/td>\n\u00b12.5\u00b0<\/td>\n<\/tr>\n
Protective height range<\/td>\n160-1800 mm<\/td>\n160-1830 mm<\/td>\n160-1827 mm in 150 mm steps<\/td>\n<\/tr>\n
Ingress protection<\/td>\nIP54-IP65<\/td>\nIP65-IP67<\/td>\nIP65 standard, IP67 waterproof variant<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Industry biometric resolution conventions for hand and body protection \u2014 based upon IEC 61496-2 detection capability classes and ISO 13857 reach-through distances \u2014 translate detection resolution to body parts as follows: 14 mm for finger, 30 mm for hand, 70 mm for leg, >70 mm for entire body presence \u2014 values referenced against ISO 13857 reach distances and the curtain emitter and a receiver pair generating infrared light beams along the protected area. These values appear consistently on Type 4manufacturer datasheets including the QJKH ENT Series. Correct resolution is whatever body part could reasonably be expected to enter the protected zone most quickly – finger on a press, hand and torso on a robot cell perimeter, entire body on a palletiser.<\/p>\n

Using a body resolution curtain ‘to save money’ on a finger-exposure risk is the kind of mismatch that results in an inspection citation.<\/p>\n

8. Cost & Total Cost of Ownership<\/h2>\n

\"8.<\/p>\n

Q: What is the price of a Type 4 safety light curtain?<\/h3>\n

Industry guides listed before 2024 frequently reference a 15-30% hardware-premium for Type 4 as compared with a similar-height Type 2 curtain,though list pricing can vary significantly by manufacturer, number of beams, and connector choice, and newer integrated Type 4 incarnationsmay have closed much of that gap. In QJKH’s ENT Series catalogue, the delta between a Type 2 (SIL CL 1) and a Type 4 (SIL CL 3) implementation of the same recommended safety height is of that order. A five-year total cost of ownership far more helpful than list pricing usually reflects an opposite relationship.<\/p>\n

It sets the stage for our high-throughput machine TCO of:<\/p>\n

5-Year TCO Components \u2014 Light Curtain Sub-system<\/strong><\/p>\n
    \n
  1. The equipment – emitter + receiver + safety relay + cable. A baseline of Type 4 +15-30% on Type 2.<\/li>\n
  2. Type 2 Nuisance-stop downtime. Type 2’s wider EAA increases the chance of an optical short circuit, with known downtime costs generally exceeding hardware costs within a year on high-throughput lines.<\/li>\n
  3. Yearly functional safety audit – over- classified Type 2 in a Type 4-required application has audit findings that are more expensive to fix than the hardware delta.<\/li>\n
  4. Insurance & OSHA \/ EU regulatory exposure – under-classified protective devices continue to be a reporting trend towards greater citation severity in machine guarding inspection documents.<\/li>\n
  5. Replacement \/ mission time<\/strong> \u2014 both Types are typically rated for a 20-year mission time per ISO 13849-1, but the wider EAA on Type 2 often drives earlier replacement in dusty or reflective environments.<\/li>\n<\/ol>\n<\/div>\n

    Customers can run their own numbers in our Type 2 vs Type 4 cost comparison calculator<\/a>, which weights hardware delta against nuisance-stop frequency and an industry-typical labour rate.<\/p>\n

    9. Common Selection Mistakes from the Field<\/h2>\n

    \"9.<\/p>\n

    From two decades of application engineering and over fifty countries of ENT Series deployments, six selection patterns repeat. None are abstract \u2014 each has shown up in real RFQs and audit reports.<\/p>\n