When choosing the safety features for a high speed door, photocells and light curtains are two non-contact detection devices that may be specified around the opening. Both can signal the door control system when a person, vehicle or object is in the way, but they provide different levels of coverage.
If you asked us which one is better, we’d first look at how the doorway is used. An opening used by forklifts on a predictable route can present different risks from one shared by vehicles, pallets and pedestrians.
This guide explains the practical differences between photocells and light curtains, including the area they monitor, how they are positioned and where each may be more suitable.
Photocells vs Light Curtains at a Glance
| Factor |
Photocell |
Light curtain |
| Detection method |
Usually one beam |
Multiple beams |
| Detection area |
One fixed line |
Wider vertical field |
| Positioning |
Mounted across the opening at a chosen height |
Mounted vertically at the sides of the opening |
| Obstruction detection |
Detects objects that interrupt the beam |
Can detect objects at multiple heights |
| Typical use |
Where the required detection point is more predictable |
Where broader detection across the opening is needed |
| Common issues |
Dirt, misalignment, impact or wiring faults |
Dirt, misalignment, impact or wiring/control faults |
The main difference is the amount of the opening being monitored. A photocell checks whether something breaks one particular beam, while a light curtain can monitor a much larger vertical area.
How Does a High Speed Door Photocell Work?
A high speed door photocell typically uses a transmitter on one side of the opening and a receiver on the other.
A beam passes between the two at a chosen height. If a person, vehicle, pallet or other obstruction interrupts that beam, the door control system receives a signal and responds according to how the system has been configured.
The important limitation is that the photocell only monitors the line of the beam. An obstruction that does not pass through that line may not be detected.
How Does a High Speed Door Light Curtain Work?
A light curtain also uses a transmitter and receiver positioned across the opening, but instead of one beam it uses multiple beams over a larger vertical area.
Together, those beams create a detection field. If a person, vehicle or object interrupts one or more of them, the door control system can respond.
Because the detection area extends across multiple heights, a light curtain can monitor more of the opening than a single photocell beam.
What’s the Main Difference Between a Photocell and a Light Curtain?
The main difference is how much of the opening each system monitors.
A photocell detects an obstruction only when it breaks the beam at the height where that beam has been positioned. A light curtain uses multiple beams, so it can monitor a wider vertical area instead of relying on one fixed detection line.
This means positioning is especially important with a photocell. For example, a beam set at one height might detect a person or the body of a vehicle but miss a lower object that passes underneath it.
A light curtain provides broader coverage across different heights, which can be useful where people, vehicles or goods of different sizes regularly pass through the opening.
That does not automatically make a light curtain the better option. The right choice depends on the area that needs to be detected and how the opening is actually used.
How Does Positioning Affect Detection?
Where the sensor is positioned determines which part of the opening it can actually monitor.
With a photocell, the height of the beam is particularly important because only objects that interrupt that line will be detected.
With a light curtain, the height and extent of the detection field determine how much of the opening is covered.
In both cases, the positioning should reflect how people, vehicles and goods actually move through the doorway rather than being treated as a one-size-fits-all setup.
When Might a Photocell Be Suitable?
A photocell may be suitable where the required detection point is relatively predictable and traffic tends to pass through a consistent part of the opening.
For example, it may be appropriate where:
- A specific beam height provides the required detection
- Traffic follows a consistent route through the doorway
- The objects passing through the opening are relatively predictable in size and position
- The photocell forms part of the wider safety arrangement around the door
The suitability still depends on the opening, traffic and wider door setup rather than the photocell being the default choice.
When Might a Light Curtain Be More Appropriate?
A light curtain may be more appropriate where broader detection is needed across the opening.
This can be useful where:
- People, vehicles or goods pass through at different heights
- The opening is used by mixed traffic
- A larger vertical area needs to be monitored
- A single photocell beam could leave gaps in detection
The wider detection field can give more coverage than one fixed beam, but the final choice should still reflect the specific risks and operating conditions at the opening.
What Can Cause Photocells or Light Curtains to Stop Working Properly?
Both photocells and light curtains rely on their sensors remaining clear, correctly aligned and connected to the door control system.
Problems can be caused by:
- Dirt or debris covering the sensor
- Misalignment between the transmitter and receiver
- Impact damage from vehicles or equipment
- Loose or damaged wiring
- Damaged mounting brackets
- Faults elsewhere within the door control system
Some problems may be obvious, such as a damaged sensor or bracket, while others can cause intermittent faults or unexpected door behaviour.
If a photocell or light curtain is not detecting correctly, the cause should be properly investigated rather than components being adjusted or replaced by trial and error.
BID Group provides industrial door servicing and repairs, including inspection and fault diagnosis for high speed doors and their safety systems.
Are Photocells and Light Curtains the Only Safety Devices on a High Speed Door?
No. Photocells and light curtains form part of the wider safety arrangement around a powered door and should not be considered in isolation.
HSE guidance recognises that powered doors and gates may require a combination of suitable safety features to prevent people being struck or trapped during operation.
For a wider look at powered-door safety and compliance, read our guide to High Speed Door Safety Standards.
Photocell or Light Curtain: Which Is Right for Your High Speed Door?
There isn’t one option that is right for every high speed door.
The most suitable system will depend on factors such as:
- How much of the opening needs to be monitored
- How people, vehicles and goods approach the doorway
- The sizes and types of traffic passing through
- The existing door and control setup
- The wider risk assessment for the opening
A photocell may provide the required detection where traffic and the detection point are predictable, while a light curtain can provide broader coverage across multiple heights.
The choice should therefore be based on the individual opening rather than assuming one system is automatically better than the other.
Need a High Speed Door Sensor Checked or Assessed?
If you’re unsure whether an existing photocell or light curtain is working correctly, BID Group can inspect the door and its safety systems as part of our industrial door service and repair support.
If you’re specifying a new door and need advice on the appropriate detection setup, talk to our team about your high speed door requirements.
High Speed Door Photocells vs Light Curtains FAQs
What is the main difference between a photocell and a light curtain?
A photocell usually monitors one beam at a fixed height, while a light curtain uses multiple beams to monitor a wider vertical area.
Does a photocell detect the whole doorway?
No. A photocell detects obstructions that interrupt its beam, so objects passing above or below that line may not be detected.
How many beams does a light curtain use?
Light curtains use multiple beams rather than a single fixed beam. The number and spacing will depend on the particular system and the area it is designed to monitor.
Is a light curtain better than a photocell?
Not automatically. A light curtain provides broader detection, but the right choice depends on the opening, traffic and area that needs to be monitored.
Where is a photocell fitted on a high speed door?
Photocell components are typically positioned on opposite sides of the opening so a beam passes across the doorway at the required height.
Where is a light curtain fitted?
Light curtain transmitter and receiver units are typically mounted vertically at opposite sides of the opening, creating a detection field between them.
Can dirt or misalignment cause sensor faults?
Yes. Dirt, debris, impact damage or misalignment can interfere with photocells and light curtains, as can wiring or control-system faults.
What should I do if my high speed door sensor stops working?
If a photocell or light curtain is not detecting correctly or the door is behaving unexpectedly, arrange for the system to be professionally inspected rather than relying on trial-and-error adjustments or replacement.
