Both Type 3 and Type 4 light curtains are safety devices used to protect people working near hazardous machines by detecting if someone or something enters the danger zone. They work on the same basic principle — a transmitter sends infrared light beams to a receiver, and when any beam is blocked, the machine stops immediately. However, the main difference between Type 3 and Type 4 lies in their safety performance level, reliability, and application area.
A Type 3 light curtain provides a medium level of safety protection. It is designed to meet Performance Level “d” (PL d) or Safety Integrity Level 2 (SIL 2) according to international safety standards. These light curtains are suitable for applications where the risk of injury is moderate and not life-threatening. They are often used in semi-automated systems, packaging machines, or material-handling areas where human interaction with machines is limited. Type 3 models usually have a simpler design with less redundancy in their internal circuits, which makes them more cost-effective but slightly less fault-tolerant than Type 4.
A Type 4 light curtain, on the other hand, provides a higher level of protection and is designed for Performance Level “e” (PL e) or Safety Integrity Level 3 (SIL 3) applications. It offers full redundancy and internal monitoring to detect any internal faults immediately. This ensures that even if one component fails, the safety function will still work correctly. Type 4 light curtains are required in high-risk machines, such as robotic work cells, metal presses, or cutting systems, where a person could be seriously injured if the safety system fails. They have faster response times, stronger self-diagnosis capabilities, and meet stricter safety regulations.
In simple terms, both types stop machines when something breaks the light beam, but Type 4 light curtains offer higher reliability and are suitable for high-risk applications, while Type 3 light curtains are designed for medium-risk applications where the safety requirement is not as critical.
If you’re setting up a machine with potential for serious injury, a Type 4 light curtain is the correct and safer choice. For lower-risk or secondary safety zones, a Type 3 light curtain can provide adequate protection with lower cost and simpler installation.