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Type 2 vs Type 4 Safety Light Curtains: Risk-Based Selection Decision Tree
01 · Safety Light Curtain Guide
Type 2 vs Type 4 Safety Light Curtains
The main difference between a Type 2 and Type 4 safety light curtain is the level of safety performance and fault behaviour required by IEC 61496—not simply resolution, sensing range or the number of processors inside the device.
Type selection should follow the required safety performance of the machine application. A higher Type classification can support a higher maximum safety level, but the complete safety function still depends on risk assessment, control-system design, stopping performance and validation.
Current CCH Product Scope
CCH’s current international ENT safety light curtain range is Type 4. Type 2 and Type 3 are discussed in this article for standards education and engineering comparison; they are not presented as current CCH international product lines.
IEC 61496 Comparison
Same sensing concept. Different maximum safety capability.
Type 2
Maximum application capability:
PL c / SIL CL 1
IEC 61496 Classification
Type 2
ISO 13849-1
Applications up to PL c
IEC 62061
Applications up to SIL CL 1
Effective Aperture Angle
Up to ±5° at ≥3 m
Type 4
Maximum application capability:
PL e / SIL CL 3
IEC 61496 Classification
Type 4
ISO 13849-1
Applications up to PL e
IEC 62061
Applications up to SIL CL 3
Effective Aperture Angle
Up to ±2.5° at ≥3 m
Selection Rule
Select the device Type from the required PLr, risk assessment and applicable machine standard—not simply from the machine name, price or detection resolution.
02 IEC 61496 Classification
Type 2, Type 3 and Type 4 Light Curtains
IEC 61496 defines Type classifications for electro-sensitive protective equipment. Current light curtain technology includes Type 2, Type 3 and Type 4 devices.
Type 2
Up to PL c
ISO 13849-1
Applications up to PL c
IEC 62061
Applications up to SIL CL 1
Type 2 devices provide a lower maximum safety capability than Type 3 or Type 4 devices and are appropriate only where the required safety performance does not exceed that capability.
Type 3
Up to PL d
ISO 13849-1
Applications up to PL d
IEC 62061
Applications up to SIL CL 2
Type 3 light curtains are part of the current IEC 61496 framework and provide an intermediate safety capability between Type 2 and Type 4.
Type 4
Up to PL e
ISO 13849-1
Applications up to PL e
IEC 62061
Applications up to SIL CL 3
Type 4 provides the highest Type classification commonly used for safety light curtains and supports applications requiring safety performance up to PL e / SIL CL 3.
IEC 61496-1
Defines general requirements and tests for electro-sensitive protective equipment.
IEC 61496-2
Defines particular requirements for active opto-electronic protective devices such as safety light curtains.
A Type classification establishes the maximum device capability. It does
not by itself prove that the complete machine safety function achieves
PL c, PL d, PL e or a particular SIL level.
03 Do Not Mix the Terms
Type, Category, PL and SIL Are Not the Same Thing
These terms belong to related but different parts of functional-safety engineering. Treating them as interchangeable can lead to incorrect device selection or incorrect claims about the complete machine safety function.
IEC 61496
Type
Classification of the electro-sensitive protective device itself, including its required safety performance, testing and fault behaviour.
ISO 13849-1
Category
Describes structural characteristics of the safety-related control system architecture and its behaviour under relevant faults.
ISO 13849-1
PL / PLr
PL describes the achieved performance of a safety function. PLr is the required Performance Level determined for the application.
IEC 62061
SIL / SIL CL
Safety Integrity Level concepts are used within another functional safety framework for safety-related control functions.
Critical Distinction
Do Not Convert the Labels Mechanically
Type 2 ≠ Category 2
A Type 2 safety light curtain is not called “Type 2” because the complete machine uses ISO 13849 Category 2 architecture. Likewise, a Type 4 light curtain does not automatically make the complete safety function Category 4 or PL e.
What Determines the Achieved Performance Level?
PL Is a Property of the Complete Safety Function
Evaluation under ISO 13849-1 considers the safety-related control system as a whole. Important engineering concepts include:
Category
Safety-related architecture and fault behaviour
MTTFd
Reliability contribution of relevant components
DCavg
Average diagnostic coverage of the safety system
CCF
Measures addressing common-cause failures
PFHd
Probability of dangerous failure per hour for the safety function
A Type 4 safety light curtain can be suitable for use in a safety
function requiring a high Performance Level, but the achieved PL still
depends on the complete SRP/CS design, downstream safety logic and output
devices, diagnostics, reliability calculations and validation.
04 Device Behaviour
Fault Detection & Effective Aperture Angle
IEC 61496 Type classification is defined by required safety performance, testing and fault behaviour—not by a universal hardware rule such as “one CPU versus two CPUs.” Manufacturers may use different internal architectures to meet the applicable Type requirements.
Type 2
Periodic Testing & Lower Maximum Safety Capability
Type 2 devices must satisfy the testing and fault-behaviour requirements applicable to their classification. Their maximum use is limited to safety functions requiring performance up to PL c / SIL CL 1.
Type 4
More Demanding Fault-Detection & Fault-Behaviour Requirements
Type 4 devices must satisfy more demanding requirements for fault detection and behaviour under relevant faults. This supports use in safety functions requiring performance up to PL e / SIL CL 3 when the complete safety architecture is designed accordingly.
The number of processors, diagnostic architecture and internal circuitry
are implementation choices made by the manufacturer. They should not be
used as the general definition of Type 2 or Type 4.
Effective Aperture Angle · EAA
Type 2 and Type 4 Also Differ in Optical Requirements
Type 2
IEC 61496-2 Comparison
Up to ±5°
Effective aperture angle under the applicable comparison condition at operating distances of 3 m or greater.
Type 4
IEC 61496-2 Comparison
Up to ±2.5°
Narrower effective aperture angle under the corresponding comparison condition at operating distances of 3 m or greater.
The narrower optical angle associated with Type 4 requirements helps
reduce the possibility that reflected light forms an unintended
optical path around an obstruction. Product-specific installation
instructions must still be followed.
Reflective machine panels, polished metal, mirrors and other highly
reflective surfaces can affect safety light curtain installation.
Maintain the minimum distance from reflective surfaces specified in the
selected product’s operating instructions.
05 Risk Assessment
When Is a Type 4 Safety Light Curtain Required?
The correct question is not “Which machine normally uses Type 2?” but “What safety performance is required for this safety function?”
01
Identify the Hazard
Define the hazardous motion, possible injury and how personnel can access the hazard zone.
02
Determine Required PLr
Use the applicable risk-assessment method and machine requirements to determine the required safety performance.
03
Check Type-C Standards
A machine-specific Type-C standard may impose particular safeguarding requirements or required safety performance.
04
Select the ESPE Type
Choose a device Type whose maximum capability is sufficient for the required safety function.
Selection Principle
If the Required Performance Exceeds Type 2 Capability, Type 2 Is Not Suitable
A Type 2 light curtain is limited to applications up to PL c / SIL CL 1. If the required safety function is PL d, PL e, SIL CL 2 or SIL CL 3, the protective device must have adequate capability and the complete safety architecture must be designed accordingly.
Packaging Machinery
Assess the specific hazard and required PLr.
Conveyor Systems
Do not assign Type based only on the machine category.
Robot Cells
Consider access routes and the complete safeguarding concept.
Point of Operation
Evaluate severity, exposure and stopping performance carefully.
Machine names do not determine the Type. Two packaging machines can have
very different hazards, access conditions, stopping behaviour and
required Performance Levels.
06 Installation Engineering
Resolution, Safety Distance & Installation
Safety light curtain Type and detection resolution are separate design choices. Resolution affects what can be detected and influences safeguard positioning, while Type defines the device’s safety classification.
Type
Defines the safety-device classification and maximum functional safety capability under IEC 61496.
Resolution
Defines the detection capability of the light curtain. A Type 2, Type 3 or Type 4 product can exist with fine resolution; resolution alone does not identify the Type.
Safety Distance
Depends on approach geometry, total safety-system response time, detection capability, reaching conditions and the actual machine stopping performance.
Current CCH ENT Type 4 Range
Three Detection-Resolution Platforms
ENT14
14 mm detection resolution
ENT25
25 mm detection resolution
ENT45
45 mm detection resolution
ISO 13855:2024 Engineering Tool
Calculate Safety Light Curtain Separation Distance
Use our updated ISO 13855:2024 calculator to evaluate preliminary separation distance using actual response time, stopping time and reaching-distance conditions.
ISO 13855:2024 is the current international edition for positioning and
dimensioning safeguards with respect to human approach. The 2010 edition
has been withdrawn. Always validate the final installation against the
applicable standard and actual machine stopping behaviour.
07 Engineering Checklist
Type 2 vs Type 4 Selection Checklist
Before selecting a safety light curtain, verify the complete safeguarding requirement rather than comparing only price, sensing range or one headline specification.
01
Required PLr
Determine the required performance of the safety function from the machine risk assessment.
02
Type-C Standard
Check whether a machine-specific standard defines particular safeguarding requirements or minimum safety performance.
03
Detection Resolution
Select the detection capability required for the body part or access condition that must be detected.
04
Safety Distance
Determine safeguard positioning using actual device response, control response and measured machine stopping performance.
05
Reflective Surfaces
Evaluate nearby reflective materials and maintain the optical clearance required by the product instructions.
06
OSSD, EDM & Safety Circuit
Confirm the OSSD interface, external device monitoring (EDM) requirements where applicable, and compatibility with the safety relay, safety PLC and downstream switching devices.
07
Environment
Consider contamination, temperature, vibration, enclosure rating, ambient conditions and installation geometry.
08
Validation & Maintenance
Plan commissioning tests, periodic inspection and maintenance of the complete safety function.
Cost Is Not the First Decision
Type Classification Alone Does Not Predict Project Cost
Actual cost depends on protective height, detection resolution, range, functions, interfaces, accessories, certification, safety architecture and integration requirements. There is no universal percentage by which every Type 4 safety light curtain costs more than every Type 2 light curtain.
08 Common Questions
Type 2 vs Type 4 Safety Light Curtain FAQ
Common questions about IEC 61496 Type classification, PL, SIL, resolution, safety distance and CCH’s current ENT product scope.
What is the main difference between Type 2 and Type 4 safety light curtains?
The main difference is the required safety performance and fault behaviour under IEC 61496. Type 2 can support applications up to PL c / SIL CL 1, while Type 4 can support applications up to PL e / SIL CL 3 when the complete safety function is designed accordingly.
Is a Type 2 safety light curtain SIL 1 or SIL 2?
Type 2 light curtains are associated with applications up to SIL CL 1 under IEC 62061 and up to PL c under ISO 13849-1. Type 2 should not be described as a SIL 2 light curtain.
Is Type 2 the same as Category 2?
No. Type 2 is an IEC 61496 classification of the protective device. Category 2 is an ISO 13849-1 architecture concept for the safety-related control system. They are different classifications.
Does a Type 4 light curtain automatically make a machine PL e?
No. The light curtain is only one part of the safety function. The achieved Performance Level depends on the complete control architecture, safety outputs, logic, final switching devices, diagnostics, reliability and validation.
Are there Type 3 safety light curtains?
Yes. Type 3 light curtains exist under the current IEC 61496 framework and can support applications up to PL d / SIL CL 2.
Can a Type 2 safety light curtain have 14 mm resolution?
Yes. Type classification and detection resolution are different characteristics. Type 2, Type 3 and Type 4 light curtains can exist with fine detection resolutions, depending on the product design.
Is Type 4 always required for machine guarding?
Not automatically. The required device capability should follow the machine risk assessment, required PLr and any applicable machine-specific Type-C standard.
Is a Type 4 safety light curtain safer than Type 2?
Type 4 has a higher maximum safety capability and more demanding fault-behaviour requirements. However, correct safeguarding still depends on the complete system design and installation.
Is Type 4 always more expensive than Type 2?
Product Type alone does not determine price. Cost varies with protective height, resolution, range, functions, interfaces, accessories, certification, manufacturer and integration requirements. There is no universal Type 4 price premium.
Why is effective aperture angle important?
Effective aperture angle relates to the optical directional behaviour of the emitter and receiver. A narrower angle helps reduce the influence of unintended optical paths caused by nearby reflective surfaces.
How do I calculate safety light curtain distance?
Safety distance depends on the applicable approach geometry, overall system response time, machine stopping time, detection capability and reaching conditions. For suitable vertical ESPE applications, use the current ISO 13855:2024 method and validate the final installation.
Does CCH currently sell Type 2 safety light curtains?
CCH’s current international ENT safety light curtain range is Type 4. Type 2 is covered on this page for standards education and product-selection understanding, not as a current CCH international product line.
What Type are CCH ENT safety light curtains?
The current CCH ENT international safety light curtain range is Type 4, with ENT14, ENT25 and ENT45 resolution platforms for different detection requirements.
Current CCH Safety Light Curtain Range
Need a Type 4 Safety Light Curtain for Your Machine?
Explore the ENT Type 4 range or discuss your required resolution, safety distance, protective height and control-system integration with CCH.