🕒 4 min read • 🟡 Intermediate • Educational Resource
The Standard
ANSI B11.19 identifies presence-sensing devices, including safety light curtains, as engineering control devices that may be used as part of a machine's risk reduction strategy when properly selected, installed, and maintained.
A light curtain is intended to detect a person or body part entering its sensing field and initiate the appropriate safety function before exposure to hazardous motion can occur. It is one of many possible safeguarding methods and must be applied based on the machine-specific risk assessment.
Proper application includes consideration of detection capability (finger, hand, or body detection), safety distance, mounting location, reset functions, and the machine's stopping performance.
Note: A light curtain does not automatically make a machine safe. Its effectiveness depends on proper application, integration, safety distance, and machine stopping performance.
The Practical Translation
A light curtain is not an invisible guard—it's an electronic sensing device that tells the machine someone has entered a hazardous area.
Breaking the beams does not instantly stop the hazard. The machine still requires time to stop, which is why the light curtain must be located an appropriate safety distance from the hazard.
The size (resolution) of the light curtain matters. A finger-resolution light curtain is intended to detect smaller body parts than a hand- or body-detection curtain, making proper selection critical for the application.
Light curtains often improve productivity by allowing material loading and unloading without opening physical guards, but they should never be viewed as a shortcut around proper safeguarding.
Every light curtain installation should be evaluated as part of the complete safety system—including the machine's stopping performance, reset strategy, operator access, and control reliability.
Ask yourself:
Is the light curtain installed far enough from the hazard to allow the machine to stop before someone can reach it?
Is the detection capability appropriate for the body part being protected?
Could someone reach around, under, over, or through the sensing field?
Does clearing the light curtain automatically restart the machine, or is an intentional restart required where appropriate?
Has the machine's stopping performance been verified since the light curtain was installed?
The Takeaway
A light curtain does not prevent access—it detects access.
Its purpose is to stop or prevent hazardous motion before a person can be exposed to the hazard, but it can only do that when it is correctly applied as part of the overall safeguarding strategy.
Compliance establishes the performance requirements for presence-sensing devices. Practical risk reduction asks whether your light curtain is positioned, integrated, and maintained so it can actually protect people—not just detect movement.
Want to learn more?
Explore our guide on Light Curtains: Selection, Safety Distance & Best Practices to learn how light curtains work, common application mistakes, safety distance considerations, and when a physical guard or another safeguarding method may be a better solution.
