What is the difference between Type 2 and Type 4 safety light curtains?
The main difference between Type 2 and Type 4 safety light curtains lies in their level of safety integrity, internal monitoring, and application suitability. Both are used to protect operators from dangerous machinery by creating an invisible wall of infrared light beams that stop the machine when interrupted. However, they are designed for different risk levels based on international safety standards.
A Type 2 safety light curtain is meant for low- to medium-risk applications. It meets Performance Level PL c and Safety Integrity Level SIL 1 according to IEC 61496-1/-2 standards. Type 2 curtains perform self-checks mainly at power-up but not continuously during operation. This means if a fault occurs while the machine is running, it might not be detected immediately. Type 2 models are cost-effective and ideal for simple machines like small assembly systems, pick-and-place stations, or semi-automatic packaging equipment where the risk of severe injury is low.
In contrast, a Type 4 safety light curtain is designed for high-risk machinery. It meets Performance Level PL e and SIL 3, offering the highest level of reliability and fault detection. Type 4 curtains constantly monitor their internal circuits and can detect failures instantly, even during operation. They are built with redundant microprocessors, dual safety channels, and continuous diagnostics. This makes them suitable for dangerous applications such as metal presses, robotic cells, injection molding machines, and automated production lines.
In simple terms, Type 2 = basic protection for low-risk areas, while Type 4 = advanced protection for high-risk machines. If a safety system failure could cause serious injury or death, Type 4 light curtains are mandatory. They ensure faster response, higher fault tolerance, and complete compliance with global safety regulations — making them the industry standard for critical automation safety.