Light Curtain Resolution: 14 mm vs 30 mm and Body Protection
Short answer: start with 14 mm when a finger can reach the hazardous motion, and 30 mm when finger access is prevented but a hand or arm can enter. Whole-body access protection is a separate design problem; resolution alone never establishes a safe installation.
- Answer-first 14 mm / 30 mm comparison
- Current ISO 13855:2024 context
- Supplier-ready enquiry checklist
Match the smallest reachable body part first
Use as the starting point when fingers can reach toward the hazard through the protected opening.
Use only when the machine geometry prevents finger-only access to hazardous motion.
Use a perimeter or access-guarding design with reset, presence and reach-path controls.
What does light curtain resolution actually mean?
Light curtain resolution, also called detection capability, is the diameter of the smallest opaque test object the device is designed to detect anywhere within its specified protective field. A 14 mm rated device is therefore evaluated for a smaller object than a 30 mm device.
Resolution is not the same as operating range, protective height, housing length or mounting distance. It is also unsafe to estimate resolution by looking at the visible gap between lenses. Use the certified value on the product label, data sheet and operating instructions.
Compare the protection purpose before comparing price or range
The correct choice starts with the risk assessment and the smallest body part that can reach the hazard before dangerous motion has stopped.
| Selection factor | 14 mm resolution | 30 mm resolution | Engineering implication |
|---|---|---|---|
| Typical protection purpose | Finger | Hand / arm | Choose from reachable anatomy, not from machine category alone. |
| Smallest declared object | 14 mm opaque test object | 30 mm opaque test object | Confirm the exact detection capability in the selected model's certificate and manual. |
| Typical use condition | Close access where a finger can enter toward a pinch, cutting or forming hazard | Openings where finger-only access is prevented but a hand or arm can enter | Reach-over, reach-under and bypass paths can invalidate either starting choice. |
| Effect on separation distance | Normally a smaller reach-through supplement | Normally a larger reach-through supplement | Total distance still depends on system response time and other application supplements. |
| Operating range | Often shorter for a comparable product family | Often longer for a comparable product family | Operating range is a product specification, not the safety distance to the hazard. |
| Whole-body entry | Not a complete access-protection design by itself | Not a complete access-protection design by itself | Use perimeter/access protection and prevent undetected presence or restart from inside. |
“A 14 mm light curtain has beam centers exactly 14 mm apart.” That is not a reliable assumption and can produce the wrong safety-distance input.
Omron lists one F3SJ-A family with 14 mm detection capability and 9 mm beam gap, while its 30 mm version uses a 25 mm beam gap; both list a 5 mm lens diameter. Treat this as a product example, not a universal geometry formula. View the official specification.
When should you start with 14 mm, and when is 30 mm appropriate?
These are starting conditions for engineering review, not automatic approvals for a machine type.
Start with finger detection
Fine-resolution protective field- A finger can enter the opening and reach toward dangerous motion.
- The application requires close point-of-operation access.
- The calculated reach-through supplement must be minimized.
- Small products or tools do not justify muting the operator-protection requirement.
- The selected device, control architecture and performance level satisfy the risk assessment.
Start with hand / arm detection
Coarser protective field- Machine geometry prevents a finger from reaching the hazardous movement.
- A hand or arm is the smallest body part that can enter the access path.
- The available floor space accommodates the final separation distance.
- The required operating range and protective height fit the selected model.
- Reach-over, reach-under, step-through and stay-behind hazards are controlled.
30 mm hand protection is not the same as whole-body access protection
When a person can walk into a robot cell, palletizer or material-handling area, the design must detect entry and prevent exposure after the person has crossed the sensing plane. A multi-beam perimeter device or access light curtain may be appropriate, but beam positions, lower and upper field edges, reach-over, crawl-under, reset location and presence inside the cell all require evaluation.
Current ISO 13855:2024 guidance distinguishes finger/hand protection from body protection and expands the assessment of reaching distances. Do not convert a 30 mm point-of-operation curtain into “body protection” merely by installing it across a wider opening.
Choose a field and beam arrangement that cannot be stepped over, crawled under or bypassed.
Measure the total system response and calculate the separation distance for the actual approach.
Prevent automatic restart and address undetected presence between the field and the hazard.
How resolution affects the safety distance without deciding it alone
ISO 13855:2024 uses a more structured separation-distance model. The device's resolution influences the reaching-distance supplement, while the total result also depends on system response and application-specific uncertainty.
S = (K × T) + DDS + Z
The standard also addresses dynamic approaches and the movement of the hazard. Use the applicable edition, local requirements and the selected device's instructions.
The distance between the safeguard's detection zone and the hazardous zone.
Selected for the body or body-part approach described by the standard.
Includes safety-related control response, machine stopping time and any required tolerance factor.
Accounts for possible reach through, over, under or around the protective device; resolution is one input.
Allows for relevant uncertainty and application effects, such as measurement variation or braking behavior.
Use the real machine configuration, load condition, response times and mounted geometry.
Many product manuals based on ISO 13855:2010 show S = K × T + C and, for a perpendicular approach with detection capability up to 40 mm, C = 8 × (d − 14). That explains why 30 mm normally adds more reach-through allowance than 14 mm. However, ISO 13855:2024 replaced the single C term with a broader reaching-distance supplement and an application-dependent Z term. Use the older equation only when it is the valid basis for the machine and jurisdiction; do not treat it as a complete 2024 compliance calculation.
Get a practical resolution starting point
Answer three questions to identify the next engineering path. This tool deliberately does not calculate a “compliant” distance from incomplete data.
Confirm access to the hazard before selecting a resolution
Begin with the risk assessment and a drawing or photo showing every path to dangerous motion.
- Identify the smallest reachable body part.
- Measure total stopping and response time.
- Check reach-over, reach-under and stay-behind access.
Use the machine task as context, not as the final answer
The same machine type can need different protection depending on tooling, openings, approach paths, stop time and operator tasks.
Press and forming access
Finger access near the point of operation often makes 14 mm the starting point, but machine-specific standards, tooling and stop performance control the final design.
Review: finger reach, over-reach and stop timePackaging and loading
30 mm can be suitable when the opening prevents finger-only access. Product flow may require validated muting rather than an informal bypass.
Review: hand access, material flow and muting logicRobot cell entry
Whole-body entry needs access and presence safeguards, safe reset positioning and prevention of unexpected restart after someone crosses the field.
Review: entry, stay-behind space and reset visibilityAssembly workstations
Small component handling may place fingers close to motion, while fixtures and trays can create hidden paths around the field.
Review: finger path, fixture gaps and cycle initiationPalletizing openings
Material and people may share an opening. The resolution decision must be integrated with muting sensors, fencing and control of entry behind the pallet.
Review: body access, muting sequence and trapped spaceWet or reflective areas
Resolution does not solve enclosure, optical reflection or washdown issues. Select the required environmental rating and follow the device's reflective-surface limits.
Review: IP rating, reflections and cleaning exposureSix mistakes that make a correct resolution unsafe in practice
A 14 mm or 30 mm label cannot rescue a weak application design.
Confusing operating range with safety distance
The emitter-to-receiver range and the field-to-hazard separation distance are different dimensions with different purposes.
Using catalogue stop time
Measure the response of the complete installed system under the relevant load and condition; include controls and required tolerance.
Ignoring reach-over and reach-under paths
A correctly calculated reach-through distance does not control a hand passing over the top edge or a person crawling below the field.
Allowing undetected presence behind the field
When a person can stand between the curtain and the hazard, use appropriate presence detection, reset and restart prevention.
Enabling blanking without revalidation
Blanking or reduced resolution can increase the effective detection capability and therefore change the required separation distance and test method.
Applying a generic reflection distance
Reflective-surface clearance depends on the device's effective aperture angle and operating range. Follow the selected model's instructions.
What should be on a light curtain RFQ?
A useful quotation needs more than “14 mm, 600 mm high.” Send enough application data for the supplier to check resolution, dimensions, range, response and interface together.
Let XSZ review the application before you lock the model
Share the protected opening, smallest reachable body part, measured response time and control interface. We will help narrow the resolution, protective height, operating range and wiring configuration for your project.
- Machine and hazard
- 14 / 30 / access need
- Opening dimensions
- Total response time
- Operating span
- Wiring and safety control
Related XSZ light curtain resources
Move from resolution basics to product family, environment and installation-space decisions.
Light curtain resolution questions engineers ask most often
Use these answers as a selection briefing, then verify the installed machine against the applicable standards and operating instructions.
What is light curtain resolution?
Light curtain resolution, or detection capability, is the diameter of the smallest opaque test object the device is specified to detect anywhere in its protective field. It is not the same as operating range, protective height or safety distance.
Should I choose a 14 mm or 30 mm light curtain?
Start with 14 mm when a finger can reach the hazardous motion. Consider 30 mm when finger-only access is prevented and a hand or arm is the smallest body part that can enter. The final choice must also satisfy the risk assessment, required safety performance, field geometry and separation-distance calculation.
Is a 30 mm light curtain suitable for body protection?
Not by that label alone. A 30 mm light curtain is commonly used for hand or arm detection. Whole-body entry requires an access or perimeter-guarding design that also addresses beam positions, stepping or crawling around the field, reset location and undetected presence behind the sensing plane.
Is light curtain resolution the same as beam spacing?
No. Beam pitch or beam gap is a geometric product parameter, while resolution is the declared detection capability of the complete protective device. Use the certified resolution and effective resolution stated by the manufacturer rather than deriving it from visible spacing.
Does 14 mm resolution always allow closer mounting than 30 mm?
It normally produces a smaller reach-through supplement, but the final separation distance also depends on total response time, reach-over and reach-under possibilities, the approach direction, application uncertainty and the applicable standard. A fine-resolution curtain can still be mounted too close.
Can light curtain resolution be changed after installation?
The base resolution is normally fixed by the device hardware. Some models offer blanking or reduced-resolution functions, but these can make the effective detection capability coarser and require a new distance review, documented configuration and validation with the correct test piece.
Which standards apply to light curtain resolution and positioning?
IEC 61496-1 and the applicable technology-specific part address the design and testing of electro-sensitive protective equipment. ISO 13855:2024 addresses safeguard positioning relative to human approach. The machine risk assessment, ISO 13849-1 or IEC 62061, machine-specific standards and local legal requirements may also apply.
Technical references
- ISO 13855:2024 — official scope and publication status for positioning safeguards relative to human approach.
- IEC 61496-1:2020 — official scope for the design and testing of electro-sensitive protective equipment.
- Pilz: ISO 13855:2024 positioning overview — summary of the revised formula, response time and reaching-distance supplements.
- Pilz Safety Distance Calculator — an expert-use planning aid with separate 2010 and 2024 calculation paths.
- Rockwell Automation 450L user manual — manufacturer example for 14 mm finger and 30 mm hand resolution, range and legacy ISO 13855:2010 distance calculation.
- OSHA 29 CFR 1910.212 — United States general machine-guarding requirements.