This is the index for a series of articles describing safety-critical light curtains. It includes links for selection, mounting, and alignment. It also includes a teardown and description of the essential OSSD waveform used to communicate states with a safety relay. An example is the safety-rated deTec4 on the workbench as shown in Figure 1.
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Select It → Safety Devices
Difficulty: 
Engineer — difficulty levels explained
Author: Aaron Dahlen | MSEE | Senior Applications Engineer, DigiKey
Last update: 13 Mar 2026
Figure 1: Close-up of a SICK deTEC4 series light curtain.
Light Curtain Facts
Here are a few light curtain facts that I learned along the way:
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Not all light curtains are safety devices. There are applications where a light curtain sensor is the optimal solution. For example, a light curtain may be more flexible than a retroreflective sensor, as they can detect objects of multiple heights that would otherwise be missed by a single beam.
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The IR beam can be seen using a cell phone as shown in Figure 2. Note that the SICK SLG-2 is not a safety sensor. As a rule, safety light curtains are yellow.
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DigiKey sells light curtains with beam count ranging from 4 to 240.
Figure 2: The infrared beams for this non-safety SICK light curtain are visible as purple dots to a cell phone.
List of Topics
Topics are organized into clusters. Please follow the links for a detailed description of each topic:
- Finger and hand protection
- How are light curtains aligned?
- How are light curtains mounted to industrial equipment?
- Light Curtain teardown
- Light curtain OSSD waveform
Help us to help you
If you would like to know more about light curtains, please add your question in the comments section. We may answer directly or move your question to the core of this guided learning series.
Best wishes,
APDahlen
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About This Author
Aaron Dahlen, LCDR USCG (Ret.), is a Senior Applications Engineer at DigiKey in Thief River Falls. His background in electronics and industrial automation was shaped by a 27-year military career as both technician and engineer, followed by over a decade of teaching.
Dahlen holds an MSEE from Minnesota State University, Mankato. He has taught in an ABET-accredited electrical engineering program, served as coordinator of an electronic engineering technology program, and instructed military technicians in component-level repair.
Today, he has returned to his home in northern Minnesota, completing a decades-long journey that began with a search for capacitors. Read his story here.