Class 1 to Class 4: Reading a Laser's Label for Real Power, Hazard Distance and Legal Status
The class marking tells you the accessible output band, not the distance the beam remains hazardous. A 5 mW Class 3R pointer at 1.5 mrad divergence stays above the exposure limit for about 10 metres; a 1 W Class 4 module at the same divergence stays hazardous for 149 m. Class also says nothing about eyewear, because optical density has to be matched to wavelength, not to power alone.
A laser class is a band of accessible output power. It is not a hazard distance, and the two get confused constantly because the class is printed on the housing and the hazard distance almost never is.
The number that matters for planning a bench, a garage or a back garden is the nominal ocular hazard distance — NOHD — the range beyond which the beam has spread enough that a direct hit no longer exceeds the maximum permissible exposure. For a visible continuous-wave beam it falls out of four inputs: optical power at the aperture, wavelength, beam divergence and the diameter of the beam where it leaves the housing. The calculator at the top of this page runs that arithmetic. The table below is its output for the seven classes you will actually encounter.
One thing to fix before anything else. The class is assigned to the product as sold, based on what a person can be exposed to. It is not assigned to the diode. That is why a fully enclosed engraver with an interlocked lid is a Class 1 product containing a Class 4 emitter, and why lifting that lid converts it, in one movement, into an unenclosed Class 4 workstation with no controlled area around it.
What each class actually restricts
Read the accessible-output column first, then the NOHD column. Everything else follows from those two.
The NOHD figures here assume the standard visible-light case: continuous wave, 400-700 nm, a 0.25 second exposure limited by the blink reflex, a maximum permissible exposure of 25.4 W/m², a 1 mm beam at the aperture and 1.5 mrad of divergence. That divergence is typical of a decent collimated pointer. Cheap units run 3-5 mrad and give shorter hazard distances; a tightly collimated module can hit 0.5 mrad and triple the number.
Class Accessible output, visible CW Does the blink reflex protect you NOHD at 1.5 mrad Minimum eyewear Required labelling and engineering controls Where you meet it Class 1 Under about 0.4 mW accessible, or any power sealed inside an interlocked enclosure Not relevant — no hazard in normal use Zero None Class statement on the housing; no hazard symbol required Barcode scanners, CD/DVD optics, enclosed engravers and cutters Class 1M Under 0.4 mW to the naked eye; can be far higher in a wide or fast-diverging raw beam Yes unaided. No through binoculars, a loupe or a collecting lens Zero unaided; hazardous the moment an optic collects the beam None unaided; OD 2 or better if you will look through optics Do not view directly with optical instruments Fibre-optic sources, some alignment and survey emitters Class 2 Up to 1 mW, visible 400-700 nm only Yes — the 0.25 s aversion response is the entire safety case About 4 m Not required for momentary exposure LASER RADIATION - DO NOT STARE INTO BEAM, plus class, wavelength and maximum output Laser levels, plumb bobs, distance measures, presentation pointers in most of Europe Class 2M Up to 1 mW to the naked eye; higher in the unmagnified raw beam Yes unaided, no through optics About 4 m unaided; much further through a collecting optic OD 2 if optics are anywhere in the workflow Do not stare into beam and do not view with optical instruments Line and rotary laser levels with wide fan angles Class 3R Above 1 mW up to 5 mW Marginally — a full 0.25 s blink can already exceed the exposure limit by up to 5x About 10 m OD 2-3 AVOID DIRECT EYE EXPOSURE, hazard symbol, class, wavelength, maximum output The US consumer pointer ceiling (FDA Class IIIa); brighter green astronomy pointers Class 3B Above 5 mW up to 500 mW No 33 m at 50 mW, 105 m at 500 mW OD 4-5 at the emitted wavelength Hazard symbol, key switch, emission indicator, remote interlock connector, beam attenuator OEM diode modules, laboratory sources, some laser light-show heads Class 4 Above 500 mW, no upper bound No — and a diffuse reflection off matte material can also exceed the limit 149 m at 1 W, 333 m at 5 W OD 5-7, matched to wavelength The full 3B control set plus fire-hazard warning; a defined controlled area Every diode and CO2 engraver module sold, before the enclosure goes round it Find the class marking on your device, then read across. The NOHD column is the distance to plan a workspace around — inside it, a direct hit exceeds the exposure limit; outside it, it does not. Two classes are widely misread. Class 3R gets treated as harmless because it is the consumer ceiling in the United States, but a 5 mW beam exceeds the permissible exposure by a factor of five during the very blink that is supposed to protect you. Class 1M gets treated as identical to Class 1, which it is — right up until somebody puts a finder scope, a loupe or a phone macro lens in front of it.
There is also Class 1C, which covers contact devices such as consumer hair-removal units. It is not a beam class in any useful sense and does not appear in the table because it is defined by skin contact rather than a projected beam.
Where the hazard distance number comes from
NOHD is a geometry problem. A beam of power P leaves an aperture of diameter a and spreads at divergence φ. Its irradiance falls as the spot grows, and NOHD is simply the range at which irradiance drops to the maximum permissible exposure.
The working form is NOHD = (√(4P ÷ π·MPE) − a) ÷ φ, with P in watts, a in metres, φ in radians and MPE in W/m². For visible CW light and a 0.25 s aversion exposure, MPE is 25.4 W/m². The calculator on this page takes those four inputs and returns metres; the table below is what it produces across the power range consumer and shop devices actually cover.
Optical output 0.5 mrad (tightly collimated) 1.5 mrad (typical pointer) 3 mrad (budget module) 5 mrad (wide, uncollimated) 1 mW 12 m 4 m 2 m 1 m 5 mW 30 m 10 m 5 m 3 m 50 mW 98 m 33 m 16 m 10 m 100 mW 140 m 47 m 23 m 14 m 500 mW 315 m 105 m 52 m 31 m 1 W 446 m 149 m 74 m 45 m 5 W 999 m 333 m 167 m 100 m Read down your device's optical output, then across to its divergence. If the divergence is not on the spec sheet, assume 1.5 mrad for a pointer and 3 mrad for an unbranded module, and treat the result as a floor. Divergence moves this number more than power does. Going from 1.5 mrad to 0.5 mrad triples the hazard distance at every power level, which is why a well-collimated 5 mW pointer is genuinely more dangerous at range than a sloppy 50 mW module — the sloppy one has thrown its energy away by 10 metres.
Two adjustments matter for invisible beams. There is no blink reflex at 808 nm, 1064 nm or 10.6 µm, so the assumed exposure time rises from 0.25 s to 10 s and the permissible exposure drops accordingly. And the wavelength correction factors in the standard shift the MPE around across the near-infrared. If your beam is invisible, do not use the visible-light table — feed the actual wavelength into the calculator and let it apply the correction. Then assume the answer is optimistic, because you will not know you are in the beam.
Optical density has to match the wavelength, not just the power
Laser eyewear works by absorbing a specific band. A pair of orange goggles that gives OD 6 at 445 nm may give OD 0 at 1064 nm, and will happily let a fibre laser through while you feel protected. This is the single most common safety mistake in a home laser shop, and it is entirely avoidable by reading the two numbers printed on the frame arm: the wavelength band and the OD within it.
OD is a base-10 log of attenuation. OD 4 cuts the beam by 10,000x, OD 6 by a million. The requirement is log₁₀(irradiance ÷ MPE), so it climbs slowly with power — which is why a 5 W blue diode needs only one more OD step than a 500 mW one.
Wavelength Typical device at that wavelength Optical output band Minimum OD Lens appearance The trap 405 nm violet Violet pointer, some resin-cure sources 1-5 mW OD 2-3 Orange or amber Looks dimmer than it is — the eye is poorly sensitive here, so perceived brightness understates the hazard 445-450 nm blue Diode engraver and cutter modules 1-10 W optical OD 5, use OD 6 Deep orange or red-brown The goggles bundled with a machine are often unrated novelty items with no OD or wavelength printed at all 520 nm green diode Direct-diode green pointer, green laser level 1-5 mW OD 2-3 Red or magenta Green looks roughly 30x brighter than red at the same power, so people assume the green one is stronger when it usually is not 532 nm green DPSS Astronomy pointer, older green pointers 5 mW-1 W OD 3 at 5 mW, OD 5 at 1 W Red or magenta Cheap DPSS units skip the infrared filter and leak substantial invisible 808 nm and 1064 nm alongside the green. Eyewear must block those too 635-660 nm red Red pointer, red alignment modules, laser levels 1-100 mW OD 2-4 Blue or blue-green 660 nm reads much dimmer than 635 nm at identical power; brightness is a terrible proxy for hazard 808 nm infrared DPSS pump diodes, some illuminators Varies OD 4-5 Usually near-clear or pale green Completely invisible. No aversion response, so the exposure assumption rises from 0.25 s to 10 s 1064 nm infrared Fibre laser marking heads 20-50 W OD 6-7 Near-clear or pale green Passes straight through ordinary safety glasses and through the front element of any camera or phone you point at the work 10.6 µm CO2 CO2 tube cutters and engravers 40-150 W OD 5-6 Clear polycarbonate or acrylic Far infrared is absorbed by common plastics, which is why the enclosure window is clear. Ordinary spectacles help; the eyewear question here is mostly about the reflected pilot beam, not the CO2 line Match the row to the emitted wavelength, buy at or above the stated OD, and confirm both figures are permanently marked on the eyewear itself. Anything sold without a printed wavelength band is a tinted lens, not laser eyewear. A shop running both a 10 W blue diode and a 50 W fibre marker needs two separate pairs, or one dual-band pair explicitly rated for both. There is no single lens that covers 450 nm and 1064 nm at high OD while leaving enough visible transmission to see the workpiece.
Your Class 1 engraver contains a Class 4 laser
This is the part that catches out hobby owners. Classification applies to accessible emission. Put a Class 4 diode inside a sealed box with an interlocked lid and a filtered window, and the product classifies as Class 1 — genuinely, correctly, and with no safety sleight of hand, because nobody can get at the beam.
Remove the lid to fit a taller workpiece and the classification is void. So is the assumption behind every safety decision made around that machine. The module has not changed; the controlled area has vanished.
Open-frame engravers, which most entry diode machines are, never had the enclosure in the first place. They ship as Class 4 devices with a pair of tinted glasses in the box and a sticker on the gantry. That is legal in most markets. It is also why the hazard distance in the table above is the relevant number for anyone with one on a garage bench near a window.
The site's Delivered Light Index treats an unenclosed machine and an interlocked one as fundamentally different products even when the emitter is identical, because the delivered hazard is what is being scored, not the part number.
While we are here: the wattage on the box of a diode engraver is almost never optical output. A machine advertised as 20 W is typically quoting electrical input to the module, with optical output at the workpiece nearer 4-5 W. For classification and NOHD, only the optical figure counts. Feed the optical number into the calculator, not the marketing one.
What a missing label tells you
Compliant devices carry a permanent explanatory label giving the class, the maximum output, the emitted wavelength or wavelengths, and the standard the classification was made against. Class 3R and above add the hazard symbol. Class 3B and 4 add a set of engineering controls that cost money to implement: a key switch, an emission indicator that lights before the beam appears, a remote interlock connector, and a beam attenuator or shutter.
Those controls are the useful tell. A seller who has genuinely classified a 500 mW module has paid for a key switch. A seller who ships a 500 mW module with a push-button and a sticker reading Class 3R has not classified anything; they have guessed, or copied the label from a different product.
If the housing carries no class marking at all, treat the device by measured output. Below 1 mW, handle it as Class 2. Between 1 and 5 mW, as Class 3R. Above 5 mW, as Class 3B, and above 500 mW as Class 4 with all that implies for eyewear and beam termination.
- Class, maximum output in mW or W, and wavelength in nm — permanently marked, not on a peel-off sticker
- The classification standard referenced (an IEC 60825-1 edition, or the US 21 CFR 1040.10 equivalent)
- Hazard symbol on anything Class 3R and above
- Key switch, emission indicator, interlock connector and beam stop on anything Class 3B and above
- An aperture label marking where the beam exits, on 3B and 4 devices
- For anything sold as eye-safe: a stated NOHD in metres, or the power, wavelength and divergence needed to compute one
That last bullet is the one to insist on. Eye-safe is not a classification, not a measurement and not a claim that means anything on its own. Ask for the divergence figure. A seller who cannot supply it has never measured the beam.
Legal status moves more than the physics does
The classes are international. What you are allowed to buy, own or carry under each one is not, and the gap between jurisdictions is wide enough that the same pointer is an ordinary retail item in one country and a seized parcel in another.
Broadly: the United States permits pointers up to 5 mW under the FDA's Class IIIa designation, and above that a device may not be marketed as a pointer at all. Much of Europe expects consumer pointers to sit at Class 2, meaning 1 mW. Australia restricts importation of handheld laser devices above 1 mW without a permit. Several other markets have tightened towards the 1 mW line following aviation incidents.
None of that is legal advice and all of it changes. The practical rule: if a listing offers a 1 W handheld green pointer with free shipping and no class marking, the physics in the table above are real regardless of what the customs form says, and the NOHD is 149 metres.
If the device arrived with nothing on it
Work in this order. It takes twenty minutes and produces the two numbers you need.
First, establish optical output. A laser power meter is the only honest route; if you are buying modules regularly, a cheap thermopile head pays for itself the first time a 5 W module measures 2.8 W. Failing that, use the seller's optical figure and discount it by a third.
Second, establish divergence. Measure the beam diameter at 1 m and again at 10 m, both across the same axis. Divergence in milliradians is roughly the diameter difference in millimetres divided by the distance difference in metres. A beam that grows from 2 mm to 17 mm across 9 metres is running about 1.7 mrad.
Third, run both through the calculator with the actual wavelength. Buy eyewear one OD step above the result. Then terminate the beam — a matte black anodised plate or a firebrick at the end of the path — so the hazard distance never leaves the bench.
The single habit worth building: never assume the number on the box is measured at the end of the optical train you are standing in front of. On this site that is the whole premise, and lasers are where it bites hardest, because the gap between the advertised figure and the delivered one is measured in metres of hazard.