Safety Light Curtain Terminology Explained: A Practical Guide for Machine Safety Design
Safety light curtains are widely used in industrial automation to protect operators from hazardous machine movements. However, many users misunderstand key technical terms such as resolution, beam pitch, or safety distance, which may lead to incorrect installation or reduced protection.
This article provides a clear explanation of the most common safety light curtain professional terms, helping engineers, system integrators, and purchasing teams make safer and more informed decisions. As a manufacturer specializing in industrial machine safety solutions, DADISICK focuses on providing certified safety light curtains, safety relays, and protective devices for global automation applications.
Core Terminology of Safety Light Curtains
Optical Beam (Infrared Beam)
A safety light curtain emits infrared beams at a fixed frequency from the transmitter. After passing through the optical system, these beams form a parallel detection field that is received by the receiver. When any beam is interrupted, the system immediately sends a safety stop signal.
Engineers can choose from a variety of industrial safety light curtains offered by DADISICK to meet their specific application requirements.
Beam Pitch (Optical Axis Distance)
Beam pitch refers to the center-to-center distance between two adjacent infrared beams.
Typical values include:
· 10 mm
· 20 mm
· 30 mm
· 40 mm
Smaller beam pitch enables detection of smaller objects, such as fingers or hands, but may require stricter installation distances.
Resolution (Detection Capability)
Resolution defines the minimum object size that can be reliably detected by the safety light curtain.
· Higher resolution = better detection precision
· Smaller resolution values are typically used for finger or hand protection
Resolution directly affects safety distance calculation and application suitability.
Protective Height (Effective Detection Height)
Protective height refers to the effective vertical detection area of the light curtain. It is usually measured from the first beam to the last beam center.
Selecting an appropriate protective height ensures full coverage of the hazardous area.
Protective Length (Detection Range / Scanning Width)
This parameter is critical for:
· Large machinery
· Conveyor lines
· Press machines
To ensure consistent performance across extended protective lengths, engineers often use wide scanning range safety light curtains that maintain beam alignment, signal stability, and detection accuracy over larger openings.
Self-Checking and Safety Control Concepts
Self-Test Function (Type 2 / Type 4)
Safety light curtains continuously monitor their internal circuits to detect failures.
· Type 2: Periodic self-testing
· Type 4: Real-time self-monitoring (higher safety level)
Type 4 light curtains are recommended for high-risk industrial applications.
Safety Controller and Relay Integration
A safety controller receives the light curtain's output signals and converts them into safety-rated relay or controller signals, ensuring mutual safety interlocking.
For these applications, safety relays designed for machine protection systems are commonly used to achieve reliable emergency stop control.
Dual-Channel Output (OSSD)
Dual-channel outputs provide two independent and synchronized safety signals. If one channel fails, the other immediately triggers a safety stop, ensuring fail-safe operation.
Manual Reset Function
After a safety interruption, the system requires a manual reset to resume operation. This prevents unexpected machine restarts and improves operator safety.
Safety Distance — The Most Critical Calculation
What Is Safety Distance?
Safety distance is the minimum distance between the safety light curtain and the hazardous zone, ensuring the machine stops before an operator can reach danger.
Incorrect safety distance is one of the most common installation mistakes.
Safety Distance Formula (ISO Reference)
Ds = K × T + C
Where:
· Ds = Safety distance (mm)
· K = Human approach speed (mm/s)
· Horizontal installation: 1600 mm/s
· Vertical installation: 2000 mm/s
· T = Total stopping time (s)
· C = Additional distance (mm), depending on resolution
Reference C Values
· Resolution 20 mm → C = 80 mm
· Resolution 30 mm → C = 130 mm
· Resolution 50 mm or above → C = 850 mm
For a deeper understanding of how stopping performance and control reliability contribute to overall system safety, it is essential to consider machine safety performance levels defined under ISO 13849-1.
Conclusion — Turning Terminology into Real Safety
Understanding safety light curtain terminology is not just a technical exercise—it directly affects machine safety, compliance, and operator protection. By mastering concepts such as beam pitch, resolution, protective height, length, and safety distance, engineers can design safer systems and avoid costly safety risks.
As an engineer working in machine safety at DADISICK, this article is written based on real application experience and daily technical support cases. Correct understanding of safety light curtain terminology is the foundation for compliant design, reliable installation, and long-term operational safety.
Related Safety Devices
Beam spacing：40mm
Number of optical axes：20
Protection height：760mm
Safety sensors for machines output (OSSD):2 PNP
Multifunctional safety relay, providing automatic/manual reset configuration and multifunctional configuration DIP switch, used for industrial field monitoring of various signals with high safety requirements.
5m distance, A technique that uses a laser beam to measure distance and create detailed maps of objects and environments.
Used for monitoring places such as safety doors and windows.
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