The standard requires that the ESPE differentiate between the intended light beam and rogue light. If you download the PDF, look at Annex A (informative). It shows you the test setup for "high frequency modulated interference." Basically, they point a high-power strobe at your sensor to see if it fails to a safe state (opens the output) or, worse, stays on (dangerous).
Always confirm the "Edition" number on the cover page of your PDF. iec 61496-1 pdf