Class 4 (IV) laser safety information

Class 4 lasers are hazardous for eye exposure. They also can burn skin and materials, especially dark and/or lightweight materials at close range. They should be used with extreme care.

For visible-light lasers, Class 4 lasers' have an output power 500 milliwatts and above. There is no upper limit for Class 4 -- this is the most hazardous laser classification.

Class 4 is the same as the Roman numeral "Class IV" you may see on some lasers' labels. At this website, we primarily use the Arabic numerals, for convenience.
Class 4 visible-beam lasers are high-powered. A Class 4 laser can cause a significant eye injury if the beam, whether direct or reflected, enters the eye.

Even staring at the diffuse reflection of a laser "dot" on a wall or other surface, may cause an eye injury within a few feet of the dot. Do not stare at the laser "dot" when it is close to you.

To prevent eye exposure, always be aware of the beam location. Keep it away from people's eyes and heads. Watch out for reflected beams from glass and shiny surfaces.

Use of laser protective eyewear is recommended, as discussed elsewhere on this page.
Avoid exposure to skin and sensitive materials. A Class 4 laser can burn skin and materials, especially dark and/or lightweight materials at close range.
A Class 4 laser can be a distraction, glare or flashblindness hazard for pilots and drivers. It may also be a potential eye injury hazard for pilots at relatively close range. NEVER aim any laser towards an aircraft or moving vehicle. This is unsafe and is illegal -- you could be arrested and jailed.
This is not a toy. Children should never be permitted to use Class 4 lasers.

Any teenager using a Class 4 laser should be continuously supervised by a responsible adult. A number of teenagers have caused eye injuries to themselves or others by misusing Class 3B and Class 4 lasers.
Even if this laser looks like a pointer or flashlight, do not use this laser for pointing purposes. Class 4 lasers are too powerful to be used as pointers. Use a Class 2 (less than 1 mW) or Class 3R (less than 5 mW) laser for pointing purposes.
SAFETY NOTICE: This website 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 published by the American National Standard Institute.

The hazard distances listed below are intended only as general guidance. This is because 1) your laser may vary from the parameters (power, divergence) listed below, and 2) information on labels or marketing materials may not always be correct. For example, studies have shown that some laser pointers may be falsely labeled to avoid regulations -- the actual power may be 10 times or more what the label indicates.

Always err on the side of safety. If your laser has not been measured by a knowledgeable and trained Laser Safety Officer, assume it is more hazardous than the label or marketing materials would indicate.
Class 4 visible-light lasers are significantly hazardous for eye exposure. They can cause burns to the retina. A person cannot turn away or blink fast enough to prevent retinal eye injury from a Class 4 laser.

Prevent all eye exposure to beams from Class 4 lasers. This includes accidental exposures -- be careful to keep the beam away from eyes and faces.

Also, remember that reflections off mirrors, glass, and shiny surfaces can be just as hazardous as the direct beam. Avoid reflected Class 4 beams the same way you would avoid the direct beam.
Some Laser Safety Facts labels will list the laser’s specific eye injury hazard distance. If this is not listed, here are some example Class 4 lasers:

  • The Nominal Ocular Hazard Distance (NOHD) for a 1000 milliwatt (1 Watt) visible-beam laser with 1 milliradian divergence is 740 ft (225 m).
  • The NOHD for a 5 Watt laser with a 1 milliradian divergence is 1640 ft (500 m).
  • Additional types of Class 4 lasers are listed in the Laser hazard distance chart.
  • You can also use the online laser hazard distance calculator to precisely determine the NOHD and visual interference distances of this laser.

If you are closer than the NOHD distance to the laser, there is a possibility of retinal damage if the direct or reflected beam enters your eye. The closer you are to the laser and the longer the beam is in the eye, the greater the chance of injury.

Color indicates the relative hazard: Red = potential injury, green = unlikely injury. Beyond the Nominal Ocular Hazard Distance, the chance of injury is “vanishingly small” according to safety experts.

The scattered light from the laser "dot" as viewed on a surface, can be an eye hazard. Avoid looking directly at the laser dot for more than a few seconds. The light is too bright if you see a sustained afterimage, lasting more than about 10 seconds.

The more powerful the laser, and the closer your eye is to the laser dot, the greater the chance of injury. This can occur during certain actions, such as aligning the beam or trying to hold the laser dot on a fixed location in order to burn a material.

Some Laser Safety Facts labels will list the laser’s specific diffuse reflection hazard distance. If this is not listed, here are some example Class 4 lasers:

  • Looking at the laser dot from a 1,000 milliwatt (1 Watt) Class 4 blue (445 nm) laser beam for more than 1 minute is an eye hazard within 1.5 ft (44 cm) of the laser.
  • Looking at the laser dot from a 10,000 milliwatt (10 Watt) Class 4 blue (445 nm) laser beam for more than 1 minute is an eye hazard within 4.5 ft (1.4 m) of the laser. Even just for 10 seconds, viewing the laser dot is a hazard within 1.8 ft (0.6 m).

If you must look at the laser dot for relatively long periods of time within the hazard distances, use laser protective eyewear as discussed elsewhere on this page.
A Class 4 laser beam can burn skin and some materials. The more powerful the laser, the faster the burn will occur. In some cases, the burn may be almost instantaneous.

Some Laser Safety Facts labels will list the laser’s specific skin injury distance. If this is not listed, here is an example Class 4 laser:

  • A 1000 milliwatt (1 Watt) Class 4 laser beam is a skin injury hazard within 39 in (1 meter) of the laser.

Avoid skin exposure to a Class 4 laser beam
, especially at close range. A skin burn can be very painful, can take long to heal, and can leave a permanent scar.
A Class 4 laser beam can cause materials to smolder or burn, especially at close range. Keep the beam moving to avoid burning materials at close range. Dark materials which absorb heat, and lightweight materials such as paper and fabric, are most easily burned by visible laser beams.

  • A 1000 milliwatt (1 Watt) Class 4 laser beam is considered a burn hazard within 26 inches (67 cm) of the laser.
NEVER aim any laser towards an aircraft or vehicle that is in motion. The bright light can flashblind, cause glare, or distract the pilot or driver. This is why aiming any laser towards an aircraft is illegal.

Some Laser Safety Facts labels will list the laser’s specific visual interference hazard distances. If these are not listed, here is an example Class 4 laser:

  • A 1000 mW (1 Watt) Class 4 laser beam can temporarily flashblind a pilot or driver, causing afterimages, within 0.7 miles (1.1 km) of the laser.
  • It can cause glare, blocking a pilot or driver's vision, within 3.1 miles (5 km) of the laser.
  • It can cause distraction, being brighter than surrounding lights, within 31 miles (50 km) of the laser.

The above calculations are for a 555 nanometer green laser with 1 milliradian divergence. These parameters are very conservative and thus result in the longest visual interference distances for a 1 Watt consumer laser.

  • The more the beam spreads out, the shorter the hazard distances. For example, for a 1 Watt 555 nm green laser pointer with a beam spread of 2 milliradians, divide the above numbers by 2 to find the visual interference distances.
  • Green is the most visible color to the human eye. It will appear brighter and more distracting than other colors of equal power. For red, divide the above numbers by about 5 to get an approximation of the visual interference distances. For blue, divide the above numbers by about 20.

Visual interference distances for other Class 4 lasers are listed in the Laser hazard distance chart. You can also use the online laser hazard distance calculator to precisely determine the NOHD and visual interference distances of this laser.

Never aim a laser at or near aircraft or vehicles, no matter what its color or power.
In the U.S., aiming a laser at or near the flight path of an aircraft is a federal felony, punishable by up to 5 years in jail and a fine of up to $250,000. Other countries, and U.S. states have similar laws for interfering with safety; such laws may be used to arrest, fine or imprison a person for aiming at aircraft and vehicles.

The power of the laser does not matter. Even if a laser's power is relatively weak, aiming ANY laser beam at an aircraft or vehicle is illegal.

Persons aiming higher-powered beams are especially likely to be caught, because the beam is very visible from the air. It is easy for police helicopters to trace the beam back to the perpetrator's location.

See this page for a selected list of the many persons who have been jailed and/or fined for aiming lasers at aircraft.
Laser glasses or goggles should be used when working with Class 4 lasers, especially at close range (within a few yards or meters). They should be selected to protect against the laser's power and wavelength.

The eyewear should not block out all of the laser's light. This is because it is necessary to see where the laser "dot" is, to safely work with the laser. Because the eyewear is blocking some or perhaps all of the laser's light (for example, a hazardous reflection) you still should use caution even when using laser protective eyewear.

As you are using the laser, any other persons in the area should also have the same type of laser protective eyewear as you.
Sunglasses are NOT laser protective eyewear. They are not rated (e.g., with Optical Density) to ensure light-attenuating protection. Most will not block enough laser light to significantly reduce hazardous exposures.

In January 2018, B.H. wrote to for advice. He had a full-color laser projector emitting a total of 3 watts of red, green and blue light. He asked what eyewear would be appropriate. Below is the answer, kindly provided by Greg Makhov of LSDI, Safety Committee chair for the International Laser Display Association.

A laser projector with 1.1 W of Red, 1.1 W of Green, and 800 mW of Blue is likely a Class 4 product, and is a hazard for skin burns as well as eye injury.

The problem with broad band visible lasers is challenging. For a red laser, we can use a blue green filter, and see in that spectrum, while blocking the red portion. For a blue laser, an orange filter will do the same.

But for an RGB laser, we can’t block red AND blue AND green simultaneously — we wouldn’t be left with much incoming light. The best we can do is attenuate (reduce) the amount of red, green, and blue to a lower level.

The level of attenuation is important. If the filter is too dark, you will not be able to see to perform adjustments, and if it is not dark enough, it will not protect your eyes.

Typical filters we have used have an attenuation of about 100 times, also called Optical Density 2 or OD2. This would reduce a 200 mW beam to about 2 mW, which is reasonably safe for 1/4 second accidental exposure. To reduce from your 3 watt laser to a similar level, we would need 1000 times attenuation. But now you are looking at something like welding glass (that is very hard to see through).

I think the best approach is to work with reduced laser power when doing adjustments, service, etc. Use lower density filters that can protect against this lower level.

I can recommend the NOIR ND1 filters - these are available with several frame styles, and are cost effective. They are polycarbonate, and with a 1% transmission, they will protect against about 200 mW laser power.

Also consider the Kentek KXL-065C filters. They are more expensive, but have glass filters instead of polycarbonate, so may be more scratch-resistant. They have the same optical density.
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Some lasers may have built-in lenses or screw-on accessories, in order to make the laser "dot" sharper or fuzzier.

Any device that can focus the dot to be sharper, or the beam to be tighter than its normal width, will increase the hazard range and the risk of injury. Use extra caution when the beam is focused.
If this laser product is a projector for displays or laser shows, please be aware of the following:
Scanning the laser beam, by moving it quickly in various patterns such as lines or circles, does NOT significantly reduce hazards.

Do not aim this laser projector directly at any person or audience area. Deliberate scanning onto an audience with a Class 3B or 4 laser is inherently hazardous.

Because the labels on consumer lasers may give incorrect information -- the wrong Class or the wrong power -- do NOT rely on the label for any safety-critical calculations. Any laser aimed into an audience-accessible area must be measured with appropriate equipment by a qualified Laser Safety Officer. The LSO will determine the laser's Nominal Ocular Hazard Distance. The audience must be further than this distance. The LSO will also determine any other safety measures to be taken; for example, continuous supervision of the area, emergency stop buttons, etc.

In addition, in the U.S. and many countries and venues, special permission is required before ANY human access to Class 3B or 4 laser beams is allowed -- even if the audience is further than the NOHD. For example, the U.S. Food and Drug Administration (FDA) requires submission and FDA approval of an audience scanning variance, before any public performance can take place.
Lasers used for demonstrations, shows, displays and entertainment are highly regulated in the U.S. Both the laser projection device and the way in which it is used (the laser show) must be certified to the Food and Drug Administration. This is for ANY laser show even if the laser beam is kept away from audience areas. Generally, shows in a private home with friends and family are not covered but all other demonstrations, shows, displays, etc. done with a Class 3B or 4 laser would require the user to submit a variance, and get FDA approval in advance before the show can proceed.

Do not perform any public demonstration, show, display or entertainment with this laser projector, without having a variance from FDA. More information is available from FDA or the International Laser Display Association.

In addition to federal laws, some states and jurisdictions also regulate laser equipment and/or usage. Contact information for state agencies is available from Rockwell Laser Industries.
At the national level, laser show safety advice is given by Public Health England, formerly the Health Protection Agency. On their website they give the following guidance (as of 27 March 2014):

The NRPB, now the Radiation Protection Division of the Health Protection Agency, has undertaken considerable research into the use of lasers in the entertainment industry. Some situations have given cause for concern, mainly because the potential or actual exposure of people, including the audience, has not been properly assessed. The use of lasers may be covered by conditions on the premises under the Licensing Act, which is enforced by the local council (district, unitary or other authority). HPA advice to such councils is that a risk assessment should be carried out to demonstrate that people are not exposed to unacceptable risks. Assessment of laser display effects used for intentionally scanning the audience is time-consuming and complex. HPA experience is that such assessments are rarely satisfactorily undertaken and the practice should not routinely take place.
Many other countries and jurisdictions have regulations regarding laser show and display usage. Venues such as concert halls may have their own requirements.

Contact all appropriate authorities to ensure your laser show meets venue and government requirements.
  • General information about laser hazards and classes (Classes 1, 1M, 2, 2M, 3R, 3B and 4)
  • A page with additional links and resources on consumer laser safety, what to do if you are injured, lasers and aviation safety, a laser pointer safety website, and laser industry groups.