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.

NOTE: If all results below are “.0”, then the calculator does not work with your browser, which is probably Internet Explorer. Please use a different, up-to-date browser.
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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 blue. 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.
( 32.8 / [mrad] ) * ( sqrt ( 0.5 * [mw] ) ) * [units]
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Laser beams slowly spread out. At the Nominal Ocular Hazard Distance (NOHD), the beam has spread enough so that the light intensity (irradiance) directly entering the eye is at the Maximum Permissible Exposure (MPE).

Within the NOHD, the irradiance will be above the MPE, which is potentially hazardous. However, 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 potential hazard — as shown by the colors in the diagram.
( ( 32.8 / [mrad] ) * ( sqrt ( 0.5 * [mw] ) ) / 3.16 ) * [units]
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The ED50 distance is 0.316 times the NOHD (a little less than 1/3 the NOHD distance).

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.”
Click for more details
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]
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The animation above shows a flashblinding exposure that can cause an afterimage.

To avoid this, within the SZED the irradiance would be below 100 μW/cm2 (0.1 mW/cm2).

Further than the SZED, the laser light is not expected to cause temporary flash blindness or an afterimage — but it will cause glare.
( ( 32.8 / [mrad] ) * ( sqrt ( 12.7 * [mw] * [vcf] ) ) ) * 4.47 * [units]
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The photo above shows glare, where it is difficult or impossible to see the runway as long as the light stays in the pilot's eye.

To avoid this, within the CZED the irradiance would be below 5.0 μW/cm2 (0.005 mW/cm2).

Further than the CZED, the laser light is not expected to cause significant or blinding glare — but it will be distracting.
( ( 32.8 / [mrad] ) * ( sqrt ( 12.7 * [mw] * [vcf] ) ) ) * 44.7 * [units]
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The photo above shows distracting laser light. It is not interfering with vision, but it can be a mental distraction for the pilot.

To avoid this, within the LFZED the irradiance would be below 50 nanowatts/cm2 (this is 0.05 μW/cm2 or 0.00005 mW/cm2).

Further than 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.
Click for more details
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.