Flight Zone distances for laser pointers
In many cases the hazard from laser pointers is not that they may damage your eyes but that they might be bright enough to dazzle or distract you while performing a safety-critical task like flying an aeroplane or driving a car. There are no European standards for this but the American flight zones can be used as a guide. The normal zone is limited by the maximum permissible exposure (MPE) and is the same as the laser safety nominal ocular hazard distance (NOHD). The other zones use the 'effective irradiance' which is the irradiance multiplied by a factor which accounts for the visual response of the eye. This is factor is 1 at 555 nm (yellowish green) and falls to zero in the UV or IR.
The flight zone limits essentially relate to the probability of distraction, glare (the impairment of vision stops when the illumination ceases) and flash blindness (there is an after-image which impedes vision after the illumination ceases).in low ambient light conditions.
Distances |
Description |
limit |
limit |
Normal Zone Exposure Distance (NZED) |
At distances greater than the NZED the effective irradiance is dim enough not to present an ocular hazard but may cause flash blindness. |
Maximum Permissible Exposure (MPE) |
Maximum Permissible Exposure (MPE) |
Sensitive Zone Exposure Distance (SZED) |
At distances greater than the SZED the effective irradiance is dim enough not to cause flash blindness but may cause glare. |
100 µW/cm 2 |
25 μJ/cm 2 |
Critical Zone Exposure Distance (CZED) |
At distances greater than the CZED the effective irradiance is dim enough not to cause glare but may cause a distraction. |
5 μW/cm 2 |
1.25 μJ/cm 2 |
Laser-Free Exposure Distance (LFED) |
At distances greater than the LFED the effective irradiance is dim enough not to cause a distraction. |
50 nW/cm 2 |
12.5 nJ/cm 2 |
The applet below, which is a much simplified version of the tool in our LaserBee laser safety software package, calculates these distances for a selection of typical laser pointers with an assumed beam diameter of 1 mm and divergence of 1 mrad. Note: an NOHD is usually calculated for an exposure time of 100 s. It is highly unlikely that a laser pointer could be shone accurately in someones eye for this length of time. You therefore have the options of using 0.25 s (the 'aversion response time') or 0.1 s to calculate the MPE on which the Normal zone is based.
If a flight zone is not listed then the laser never exceeds the relevant effective irradiance or radiant exposure limit even at its exit aperture.
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