Light Curtain Safety Distance Calculator (ISO 13855)

How far from the hazard does a light curtain have to be? The answer is the machine's total stopping time times the approach speed, plus a penetration allowance that depends on the curtain's resolution. This calculator applies the ISO 13855 and OSHA 1910.217 formulas with the standard approach speeds and penetration factors, so the mounting distance is a number rather than a guess.

Worked example: a machine that stops 250 ms after the stop signal, protected by a curtain with a 20 ms response time, has T = 0.27 s. With a 14 mm resolution curtain the penetration allowance C is zero, so S = 2000 mm/s × 0.27 s = 540 mm. Swap in a 30 mm resolution curtain and C = 8 × (30 − 14) = 128 mm, so S = 668 mm. Because the first result is over 500 mm, ISO 13855 allows a recalculation at 1600 mm/s, but never below 500 mm. Use a measured stop time from a stop-time test, not the drive's nominal figure.

The same tool carries the ISO 13857 guard opening and reach-over tables, an e-stop reference, clearance distances, a PLr risk assessment guide, and a noise exposure calculator, so a robotic cell or an inspection station can be checked in one place.

How it works
  • S = K × T + C: K = 2000 mm/s for hand and arm approach (1600 mm/s for walking approach), T = machine stopping time plus device response, C = 8 × (d − 14) mm for detection capability d up to 40 mm.
  • Guard openings and reach-over distances per ISO 13857 are on the same tool under Guard Openings.

Free, no login. Your inputs are saved in this browser. Values are engineering references — verify against manufacturer data and applicable codes before a final design.

Built by the engineers behind Sanitary robotic cells.

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Questions engineers ask

How is light curtain safety distance calculated?
S = K × T + C per ISO 13855. K is the approach speed (2000 mm/s for hand and arm approach), T is the total stopping time of the machine plus the response time of the light curtain and its controller, and C = 8 × (d − 14) mm for a detection capability d up to 40 mm.
What stopping time should I use?
The machine's measured stopping time plus the light curtain's response time and the safety relay or controller reaction. Use a value from a stop-time test on the machine, not the drive's nominal figure.
When does the approach speed drop to 1600 mm/s?
ISO 13855 starts with K = 2000 mm/s. If the result exceeds 500 mm, the distance may be recalculated with K = 1600 mm/s, but it can never be less than 500 mm.

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