How do you calculate light curtain safety distance?

Multiply hand approach speed K by the total stopping time T, add the penetration allowance C, then apply your margin. Here (2000 x 0.30) + 128 = 728 as the base, before the 1.2x safety margin is applied.

Why is hand approach speed 2000 mm/s?

ISO 13855 uses 2000 mm/s for hand/arm movement toward a hazard when the calculated distance is small, dropping to 1600 mm/s in specific cases. Using 2000 mm/s is the conservative choice for finger and hand detection curtains.

What is the penetration factor C?

C is the distance a hand or finger can penetrate through the curtain before the beams register the intrusion, and it scales with the curtain's detection resolution. Finer resolution (finger detection) gives a smaller C; coarser resolution (hand or body) gives a larger one.

How does curtain resolution change the mounting distance?

Resolution sets the penetration allowance C. A 14 mm finger-detection curtain has a small C and can mount closer, while a 40 mm hand-detection curtain needs a larger C and therefore more setback for the same stop time.

What is a safe stopping time T for a light curtain application?

There is no universal 'safe' T; you measure it. It is the full time from the beam breaking to all hazardous motion ceasing, including the curtain output, safety relay/PLC, and machine braking. Shorter T means the curtain can mount closer, saving floor space.

Light curtain vs fixed guard, which needs more distance?

Both use the same speed and stop-time terms, but their intrusion/penetration allowances differ. A light curtain adds a resolution-based penetration factor, while a fixed guard uses a reach-through allowance; the correct C for each comes from the ISO 13855 tables.

Robotics & Automation calculator

Light Curtain Safety Distance Calculator

Light curtain mounting distance is the minimum gap between a safety light curtain and the nearest hazardous motion, so the machine stops before a hand crossing the beams can reach the danger zone. Controls and safety engineers calculate it to satisfy ISO 13855 when guarding presses, robots, and automated assembly stations with opto-electronic protective devices. It depends on hand approach speed, the total time for the machine to stop after a beam is broken, and a penetration allowance tied to the curtain's resolution. Mount it too close and a fast hand beats the stop; too far and the cell footprint balloons.

What this calculator does

Estimate ISO 13855 safety distance to a light curtain from hand approach speed, system stopping time, light curtain resolution intrusion, and a margin.
Use it when placing a light curtain in front of a robot or press so the mounting distance meets ISO 13855 before commissioning and the runoff stop test.
It computes the minimum mounting distance as hand approach speed times total stopping time plus a resolution-based penetration allowance, then applies a safety margin.

Formula used

Base mounting distance = (hand approach speed K x overall system stopping time T) + intrusion C
Required light curtain mounting distance = base x safety margin multiplier

Inputs explained

Hand approach speed K:
Total stopping time T (curtain to full stop):
Depth-penetration allowance C (from resolution):
Applied safety margin multiplier:

How to use the result

Use it when placing a safety light curtain in front of a press, robot or feeder during cell design or safety commissioning.
It is a design aid: the penetration factor C, hand speed K, and stop-time T must come from ISO 13855 and a validated stop-time test, and the layout must pass a formal risk assessment before production.

Current U.S. benchmarks

Global copper trades at $13,484 per tonne (IMF via FRED, May 2026), up 41.5% in a year, and U.S. industrial electricity averages 8.66 cents per kWh. Both feed electrified-hardware unit economics.

Common questions

How do you calculate light curtain safety distance? Multiply hand approach speed K by the total stopping time T, add the penetration allowance C, then apply your margin. Here (2000 x 0.30) + 128 = 728 as the base, before the 1.2x safety margin is applied.
Why is hand approach speed 2000 mm/s? ISO 13855 uses 2000 mm/s for hand/arm movement toward a hazard when the calculated distance is small, dropping to 1600 mm/s in specific cases. Using 2000 mm/s is the conservative choice for finger and hand detection curtains.
What is the penetration factor C? C is the distance a hand or finger can penetrate through the curtain before the beams register the intrusion, and it scales with the curtain's detection resolution. Finer resolution (finger detection) gives a smaller C; coarser resolution (hand or body) gives a larger one.
How does curtain resolution change the mounting distance? Resolution sets the penetration allowance C. A 14 mm finger-detection curtain has a small C and can mount closer, while a 40 mm hand-detection curtain needs a larger C and therefore more setback for the same stop time.
What is a safe stopping time T for a light curtain application? There is no universal 'safe' T; you measure it. It is the full time from the beam breaking to all hazardous motion ceasing, including the curtain output, safety relay/PLC, and machine braking. Shorter T means the curtain can mount closer, saving floor space.

Last reviewed 2026-05-12.