Elevator Light Curtain: What Every Lift Engineer and Building Operator Needs to Know

Simply put, an elevator light curtain is an invisible safety barrier created between a closing elevator door and each individual rider passing it. With around 18 billion passenger trips on U.S. elevators annually–in just one year–a small leap in existing door safety standards translates to billions of passenger door crossings. Let this brochure show you how those infrared sensor systems operate, what the EN 81-20 and ASME A17.1 truly demand, and the most cost-effective way to specify, install, and service the unit that is right for your residential skyscraper, freight hub or hospital elevator bank.

What Is an Elevator Light Curtain — And Why Has It Replaced the Mechanical Safety Edge?

An elevator light curtain provides an optoelectronic safeguard to an elevator installation. It produces a solid line of infrared beams at the full height of the elevator door. Any obstructions such as a persons handbag hand or a childs hand will cause the beams to break and the door controller is informed to reverse or open the doors.

This is the third designers have had to protect elevator doors. The first was a single-beam type of photocell (also sometimes called an elevator photocell) which saw only one point (namely at a people’s waist level), and thus left huge blind areas above and below. Mechanical safety edges were the next step; these were rubber-coated contact strips mounted on the protected edge of the door, which only reversed if physically pressed in by something attempting to obstruct the door.

Both of these are still commonly seen in older elevators (not under compliance with current code).

What Is the Difference Between an Elevator Light Curtain and a Photocell?

A photocell usually employs 1 or 2 infra-red beams at a predetermined height and will only detect large objects at that height – anything above or below that point, and between the beams, will go undetected. A modern elevator light curtain uses anything from 32 to 159+ beams across the full width of the door aperture from 25mm to 1600mm, or even more, above the door sills. The device will detect an object down to approx 14mm – this compares with a legacy single-beam photocell which probably would have detected 100mm or more.

That is the reason why the new standards such as EN 81-20 demand that the opening device detects objects down to 50mm. Photocells, mechanical edges or side-cues, simply cannot do this.

Changing factors include the increasing stringency of safety standards internationally. As deadlines for modernization loom, the mechanical safety edge – with its rubber strips, springs and pivots is being taken out of service in preference to infra-red non-contact detection that complies with EN 81-20 and ASME A17.1 standards without the requirement for ongoing mechanical maintenance.

How Elevator Light Curtains Work — From Beam Physics to Door Reversal

An elevator light curtain is comprised of two identical parts; a transmitter located on one side of the car door opening and a receiver located on the other side. The transmitter contains a cluster of infrared Light Emitting Diodes. These are pulsed on and off in a quick sequential pattern repeating in the kilohertz range and forming a maze of invisible beams across the doorway.

The actual system, from detection to door reversal, is as follows:

1. Continuous scan: the transmitter switches each LED on and off in rapid succession. A complete scan of the door opening is generated every few milliseconds.
2. Beam interruption:
   Object entering the beams causes receiver photodiodes to shut off.
3. Signal processing: Front end microprocessor analyzes the interruption pattern, filters transient noise, and verifies obstruction.
4. Output signal: PNP or NPN output (swappable on modern units) instructs elevator door controller.
5. Door reversal: Controller halts the door motor and reverses the way.

In multi-elevator single-shaft bank installations, door-opening cross-talk must be eliminated. State-of-the-art infrared curtains employ dual frequency (A and B channel) optical synchronizers to prevent cell signals from one elevator from interacting with the adjacent unit. Industry technicians have established that elevator door-light curtain cross-talk is among the most common novice diagnosis; the solution is to assign a different frequency to each elevator.

“When you’ve got two elevators in adjacent shafts and the curtains interfere with each other, nine times out of ten it’s a frequency mismatch problem. Assign the units to different channels and there is no interference any more.”

Elevator Light Curtain Types — Beam Configuration, Profile, and Detection Patterns

Elevator door illuminator detectors are not the same. The key engineering variables defining different light curtains are optical aperture alignment, detection scheme, and probe profile. Knowledge of these variables applies to determine what size objects are covered by the system, and ensure code compliance.

Detection scheme: parallel-beam curtains have beams aimed directly across the door. Criss-cross curtains have beams angled from alternate-up and -down starting points, which even as the doors near the last couple inches of travel will maintain detection coverage; a fundamental safety advantage

Probes: modern units are slim-profile and light; flush-mount within the door track profile. Commercial units opt instead for environmental integrity with gross-profile IP65+ sealed enclosures.

EN 81-20 and ASME A17.1 — What the Elevator Safety Codes Actually Require

Elevator light curtains are safety-critical components, and must meet regional standards for each market area. ASME A17.1/CSA B44 and EN 81-20 are the largest worldwide standard bodies, and agree within margins for the most part.

Are Elevator Light Curtains Required by Code?

YES. EN 81-20(Section 5.3.6.2.1.1) mandates an overspeed protective device on any new passenger and goods elevator that detects objects down to 50 mm at elevations of from 25 mm to 1,600 mm above the sills of cars’ doors. Parallel approaches were established by ASME A17.1-2019(Section 2.13.5) and the 24 th edition of the code – ASME A17.1-2025, simply builds on the original rules for door protection; any modernization or addition on a vintage cab will very often bring owner into line with the current standard.

• EN 81-20: detection from 25-1,600 mm above sill; detection of 50 mm objects; protection remains during either the closing or opening phase
• ASME A17.1-2019 +:2.13.5 requires 2D and in new installations 3D detection
• SIL 3 / category 4 / PL e: top functional safety scores (per IEC 61508 and ISO 13849); needed for safety-critical application
• Type testing:equipment must present CE mark (Europe) or be listed to the relevant standards (North America) prior to installation. Certification by Third Party provides a thorough check.

How to Select the Right Elevator Light Curtain — The 32-Beam Decision Framework

To specify the correct elevator light curtain, compare six engineering elements of the available choices for suitability. Include any one, and you may find the product will be rejected or will have operational problems within months. The process:

1. Measure the height and width of your door opening. Typical passenger elevator door heights will be 2,000-2,100 mm; freight doors are commonly over 2,400 mm tall.
2. Determine which safety standard applies to your equipment – EN 81-20, ASME A17.1 or some other authority. This indicates what detection zone range you require and the size of satisfying object.
3. Calculate the minimum number of beams required. For 2,100 mm doors under an EN 81-20 standard, assuming 20 mm separation between beams, a total of around 80 beams will extend from 25-1,600 mm, and for 10 mm separation closer to 158 beams; minimal zero-gap detection requires closer to 32 beams to cover 25-1,600 mm in your door with multiple beams just overlapping.
4. Identify the detection range needed for your installation – a car door (transmitter and receiver on the same car door frame; 0-5 m range), landing door or freight (0-10 m or 0-16 m ranges) are variations of the same principle.
5. Ensure electrical compatibility – most modern units run off a 24 VDC power source; older units may need 220 VAC. Do you require PNP or NPN output to match a door control input?
6. Consider environmental factors – parking garages and freight areas need IP65 weatherproofing; glass walled elevator cabs expose the curtain to sunlight (with over 10,000 lux it needs to be made of materials resistant to damage); multiple elevator shafts will require dual frequency channel switching.

Experienced elevator technitians value brand and quantity above marketing data sheets. As one applies: When selecting replacement units for a customer upgrade, count the beams and know that the speed differences over the response time spectrum (6-70 ms) do not matter at typical speeds of 100 mm/s and less.

Are you ready to compare specs to system? Take an elevator light curtain selector test or copy the beam count/protection height table below to discover the right match.

Installation Best Practices and the Three Mistakes That Cause Most Field Failures

Installation should be done carefully so that a good working light curtain passes inspection on day one and continues to work reliably for ten years. Equipment installation and mounting is simple enough- mount the transmitter and receiver on existing car door rails using T-bolt or magnetic brackets- but the subtle details that technicians ignore are the root of most service calls.

• Mount transmitter/receiver on car door rails; check vertical alignment with built-in LED array
• Confirm optical axis within 2 .25″
• wire NPN or PNP outputs to door control (most modern units have a one-button configuration switch)
• Select frequency A or B to prevent cross-talk with neighboring elevators
• conduct operational test- with 50 mm calibrated test object, pass through detection zone at 25 mm, 800 mm, and 1,600 mm heights
• record settings for maintenance

A four-cassette bank of four elevators in a sixteen-elevator building profile exemplifies the reasons for network planning: multiple pairs of elevators without separate channels cause ongoing phantom door reopenings that are aggravating to tenants and time-consuming for service techs to troubleshoot.

Maintenance Schedule, Diagnostics, and When to Replace

Elevator light curtains have no moving parts, no wear surfaces. This gives them a distinct maintenance benefit over mechanical safety edges. But “low maintenance” doesn’t mean “no maintenance”. The following parameters are a compilation of industry sources and factory recommendations. Your personal maintenance schedule should adhere to your installed units manufacturer recommendation documents.

In the hands of maintenance professionals, the lifetime of an IR LED emitting source that is used in elevator light curtains has been reliably proven to be the existence indicator. When used in the style of posit IR, would be dimension of the diminuitive LED as it dims through many its of operation temperature of thousand hours can see whether the sensor will easily trigger false alarms, especially in high ambient duty conditions. Quickly do a field check: point your phone camera at the transmitter and activate. Working LEDs will give off a purple glow, dim unsteady LEDs indicate many hours of service remaining.

Frequently Asked Questions

Reviewed by CCH SHANGHAI SENSING engineering team — with over 20 years of industrial safety sensor design and manufacturing experience, including TÜV-certified elevator door protection systems.