A comprehensive resource for safe and responsible laser use

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Laser Hazard Distance Calculator

If you know the power, divergence and wavelength (precise color) of a visible, continuous wave laser, you can use the online calculator below to determine the eye hazard distances NOHD and ED50, and the Federal Aviation Administration visual interference hazard distances SZED, CZED and LFZED.

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Laser Hazard Distance Calculator
This calculator is valid only for lasers emitting visible (400-700 nanometers), continuous wave (CW) laser light over long distances. It assumes an unwanted exposure where a person moves and/or blinks within 1/4 second to avoid the light; this is a standard assumption within the laser safety field.

The milliwatt, milliradian and VCF inputs are color-coded to match the Laser hazard distance equations on which this calculator is based.
Enter the laser’s power in milliwatts.
If you know the power in watts, multiply the watts by 1000 to get milliwatts. For example, for a 1.5 watt laser, enter 1500; for a 40 watt laser enter 40000.
If you don’t know the beam divergence, use 1 milliradian for lasers under 500 milliwatts in power, and 1.5 milliradians for lasers 500 milliwatts and above.
(between 0 and 1)
Enter 1 unless you also want to calculate the non-injurious "visual interference" such as flashblindness and glare, which is based on the laser beam's color. (The human eye will perceive green light as being brighter and more interfering with vision, compared with an equivalent amount of blue or red light.) Below are the FAA Visual Correction Factors for selected laser wavelengths. For example, if your laser is the common 532 nm green, you would enter 0.8802 as the VCF. If you don’t know the laser’s wavelength, or if you want the safest, most conservative calculations, enter 1 as the VCF — this will give the longest hazard distances.
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Results are below, in black. The numbers are in the distance unit selected above, to the nearest tenth of a unit (one decimal place). Results are continuously updated as you enter new information — you do not have to click a “=‘ or “Calculate” button.
Eye hazard results
The NOHD and ED50 distances below depend only on the power and divergence of the laser.
About laser eye hazards
Laser beams get wider with distance. As the beam power becomes spread over a larger and larger area, the amount of light entering a pupil decreases:
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At some distance from the laser, the light intensity will be at the Maximum Permissible Exposure (MPE). This distance is called the Nominal Ocular Hazard Distance (NOHD).
( 32.8 / [mrad] ) * ( sqrt ( 0.5 * [mw] ) ) * [units]
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Starting at the NOHD distance, laser light directly entering the eye is at the Maximum Permissible Exposure (MPE) and is generally considered safe. Specifically, at the NOHD there is “a negligible probability of damage” according to the laser safety standard ANSI Z136.1.

The farther one gets from the NOHD, the lower the irradiance, meaning that the light is even safer.
Being exposed to laser light within the NOHD does NOT mean that a person will automatically receive an eye injury, or even is likely to have an injury. The NOHD is a “nominal” hazard distance, not an actual hazard distance. The closer a person is to the laser, the greater the chance of an injury, as shown by the colors in the diagram below.
( ( 32.8 / [mrad] ) * ( sqrt ( 0.5 * [mw] ) ) / 3.16 ) * [units]
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At the ED50 distance, there is roughly a 50-50 chance that a fixed laser beam aimed into an unmoving eye under laboratory conditions will cause the smallest medically detectable change to the retina. Such small changes can heal — just as small skin cuts and burns can heal with no adverse effect.

Between the ED50 distance and the NOHD, there would be even less of a chance of the laser beam causing the smallest medically detectable change to the retina. Beyond the NOHD, it is considered safe or “a negligible probability of damage.”
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Visual interference results
The visual interference distances depend not only on the laser’s power and divergence, but also on the Visual Correction Factor of the laser’s wavelength. That’s because the human eye is more sensitive to greens and yellows, and less sensitive to blues and reds.

These three visual interference distances are used by the U.S. Federal Aviation Administration to determine how far a laser beam can travel before it falls below the irradiance limits in a Sensitive, Critical or Laser Free zone.
( ( 32.8 / [mrad] ) * ( sqrt ( 12.7 * [mw] * [vcf] ) ) ) * [units]
Beyond the SZED, the laser light is not expected to cause temporary flash blindness or an afterimage.
( ( 32.8 / [mrad] ) * ( sqrt ( 12.7 * [mw] * [vcf] ) ) ) * 4.47 * [units]
Beyond the CZED, the laser light is not expected to cause significant or blinding glare. Even if the light is bright, it will be possible to see objects past the light.
( ( 32.8 / [mrad] ) * ( sqrt ( 12.7 * [mw] * [vcf] ) ) ) * 44.7 * [units]
Beyond the LFZED, the laser light is not expected to be distracting. It will not be brighter than other city or airport lights seen outside the cockpit window.
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To calculate beam diameter and irradiance at a specified distance, use the calculator here.
SAFETY NOTICE: The calculator above is intended for the educational, instructional and informational purposes of the user and is not to be considered a substitute for a knowledgeable and trained Laser Safety Officer (LSO) with the duties and responsibilities as defined in the ANSI Z136 standard. Consult with an LSO for safety-critical usage or special cases. While care has been taken to ensure accurate calculations, we are not responsible for errors. (If you do find errors please contact us with details.)

Additional laser hazard calculators

For a full-featured hazard distance calculator, with the NOHD, ED50, and FAA visual interference distances, click here.

To calculate beam diameter and irradiance at a specified distance, use the calculator here.

We also have information about other calculators and dedicated programs. These can analyze complex situations involving multiple simultaneous colors, pulsed lasers, non-visible lasers, and/or atmospheric attenuation.

If you are a member of the International Laser Display Association, you can use ILDA’s free online Skyzan professional laser hazard calculator.