Safety Light Curtain Types: Type 2 and Type 4 Differences

With the continuous improvement of societal awareness regarding safety, people are increasingly emphasizing measures to safeguard personal safety when operating machinery. In this trend, the introduction and widespread use of safety light curtains have significantly enhanced the level of protection, providing operators with a more reliable guarantee and effectively reducing the risk of accidental injuries.

But do you know how many types of safety light curtains there are in the world? According to the protection level, there are two types of safety light curtains, type 2 and type 4, also known as Category 2 and Category 4 safety light curtains. In this article, we will explain what they are and discuss their differences.

What is a safety light curtain?

Safety light curtain used in industrial automation

Safety light curtain is a contactless protection device to protect people against dangerous machines utilizing infrared light or laser source. Generally, a light curtain consists of an emitter and a receiver(or a reflector). Many beams of light will be emitted from the transmitter to the receiver(or reflector), and once the light is blocked by an object, the machine will stop functioning. Safety light curtains are widely used in various machinery such as hydraulic equipment and elevators, shearing machines or heavy press machines, etc.

What is type 2 safety light curtain?

The type 2 safety light curtain is a low-cost photoelectric protection device which is mainly used for protecting hands that without External Device Monitoring (EDM), it is designed for moderate to minor damage situations and machines.

What is type 4 safety light curtain?

Safety light curtain used in shearing machine

Type 4 safety light curtain is specially designed for occasions needing high protection level requirements. And type 4 light curtains have External Device Monitoring(EDM) function. It can not only detect hands, but also detect any part of the human body including finger, hand and body. Type 4 light curtain sensors have a very wide range of applications, such as high-speed conveyor belts, food processing industry, pharmaceutical industry, etc.

The differences between type 2 and type 4 safety light curtains

According to our experience, there are 4 differences between type 2 and type 4 sensors, we will explain them one by one, the following are the details:

1. Cost differences

Since type 4 safety light curtains have a higher protection level than type 2 and can detect smaller objects, thus components used in type 4 are much more advanced and the detection accuracy is higher. Therefore, the cost of type 4 safety light curtains is higher than that of type 2 safety light curtains.

2. Performance differences

The type 4 safety light curtain has dual CPU processors; the type 2 safety light curtain has a single CPU processor.

3. Fault self-diagnosis differences

The type 4 safety light curtain performs self-diagnosis for fault checking, and higher-level redundant fault mutual detection, etc.; type 2 safety light curtain can perform self-diagnosis or external periodic testing for fault checking.

4. Aperture angle differences

Type 2 safety light curtain aperture angle
Type 4 safety light curtain aperture angle

Type 2 aperture angle is 10 degrees, type 4 aperture angle is only 5 degrees according to SICK video descriptions on Youtube(Resources: This aperture angle difference makes the type 4 is more precise than type 2 safety light curtains.

5. Application range differences

Type 2 safety light curtains are suitable for low-risk occasions or machines, such as bump or scrape, knock down, pinch but not crush, or minor cuts and scrapes, while for the high-risk occasions or machines, the type 4 safety light curtains are the best choice. Although they are more expensive, this cost is negligible when compared to the operator’s life safety.


Simple put, there are two common safety light curtain types according to protection level differences, they are type 2 and type 4. Type 4 light curtain is suitable for a high level protection environment but price is expensive, while type 2 is cheap and suitable for low risk occasions but price is cheap.

Lorentzzi®, as one of China’s leading safety light curtain manufacturers, can produce both type 2 and type 4 light curtains with best product quality and moderate price. Contact us now to get our latest quotation for different protected lengths light curtain sensors.

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