Laser Beam Distances

ST Laserstrike

Laser divergence over distance

Typical 100mW Green laser pointer

Laser beam distances – irradiance limits

Nominal Ocular Hazard Distance (NOHD)
The beam is an eye hazard (irradiance above the MPE) from the laser source to this distance. Risk of eye injury. Beyond this distance the MPE is not exceeded. Maximum Permissible Exposure (MPE). 0.5mW/cm².

Sensitive Zone Exposure Distance (SZED)
The beam is bright enough to cause temporary vision impairment from the source to this distance. Beyond this distance the beam irradiance is less than the SZED irradiance limit. 100 μW/cm².

Critical Zone Exposure Distance (CZED)
The beam is bright enough to cause a distraction, interfering with critical task performance, from the source to this distance. Beyond this distance the beam irradiance is less than the CZED irradiance limit. 5 μW/cm².

Laser-Free Exposure Distance (LFED)
“The beam is dim enough that it is not expected to cause a distraction. Beyond this distance the beam irradiance is less than the LFED irradiance limit. 50 nW/cm².

Notes:
Many ‘off the shelf’ $20 green laser pointers could easily cause temporary eye damage for up to 1km from the source.
The distances for red and blue laser pointers are much shorter as these lasers are far less visible to the human eye, whereas the 532 nm green lasers are close to the eye’s maximum sensitivity at around 555 nm.