Study of Laser Pointer Safety

A selection of 20 low cost (all under £14 and most under £7) laser pointers were purchased and tested for output power and divergence characteristics.

The results have been used to evaluate the correct classification of the laser pointers, the resultant hazard distances and the distances at which the laser pointers could constitute a ‘dazzle’ hazard to an aircraft pilot or car driver.

The study has shown that not only are high power laser pointers now available at very low prices, but they are also commonly advertised as much safer and lower power devices than their actual output. The mislabelling is a concern as users may be unaware of the true hazard posed by the laser pointer, which may also be treated trivially in any workplace risk assessment. Similarly, the low prices mean that these devices are now within the purchasing power of children, with a host of safety issues resulting.

Why?

The back ground for this work goes back to between November 2008 and March 2009, when our Technical Director, John Colton, was expert witness in a court case where a police helicopter had been exposed to the beam from a basic laser pointer. As part of this work John and some colleagues at Lucid used a variety of equipment and our own laser safety software package to measure the laser power level, divergence and other parameters of this laser pointer. It was labelled as <20 mW, and was in fact outputting 8.5 mW of green laser light at 532 nm.

Shortly after this and other similar incidents, trading standards applied pressure to UK internet sellers to restrict sales to relatively safe 1 mW Class 2 laser pointers.

In April 2010, John then bought a new green laser pointer for demonstrations on our laser safety courses. This was advertised as below 1 mW, and cost around £6 including postage over the internet. When it arrived, it was labelled as <1mW power, but it was so bright that John decided to measure it. This result was 125 mW, which rather shocked us for a laser at this price level, and prompted a decision to buy a number of low cost laser pointers and carry out a study to see if this mislabelling was a one-off.

The lasers in the study

Laser pointers are now available in several colours, or wavelengths, most commonly as follows:

• blue (405 nm): newer & more expensive
• green (532 nm): lower cost and far more visible as the eye is most sensitive to green
• red (650 nm): really cheap!

We purchased 20 laser pointers: 7 red, 11 green and 2 blue.

All cost under £14, most under £7 incl delivery.

Eleven of the twenty pointers tested were purchased from within the UK, whilst the remaining nine were supplied from the China, Hong Kong or Singapore. It appears that the UK and Far East supplied lasers are very similar and all are likely to originate from the far East.

Laser Classes

In UK and EU, lasers are classified according to the table below. The class, and hazard, of a laser depends on both wavelength, the power, the spot size and the divergence i.e. how much the beam spreads out.

For laser pointers where the wavelength is visible, the source size is small and the divergence is generally low, the upper power limits for each class of laser can be readily tabulated:

Laser Class	Maximum Power Level	Summarised key descriptive phrase
Class 1	0.39 mW	Safe to view with the unaided eye
Class 1M	NA	Safe to view with the unaided eye but not with optical aids (‘Magnifiers’)
Class 2	1 mW	Visible lasers where the blink reflex should ensure safety
Class 2M	NA	Visible lasers where using optical viewing aids could be hazardous
Class 3R	5 mW	Lasers were direct viewing could be hazardous, but safety requirements are ‘Relaxed’
Class 3B	500 mW	Direct ‘intrabeam’ viewing is always hazardous
Class 4	no upper power limit	Severe eye hazard, and also a potential diffuse reflection hazard, fire and skin hazards

This table shows the classification that is used in the UK , the EU and most of the rest of the world (IEC 60825:2007-1). The US now uses a very similar system with the same classes (Ansi Z136.1-2007). Prevously, the US had a different class system, where classes were denominated in lower case letters and roman numerals, such as class IIIa. There is no direct translation, but class llla corresponds roughly to class 2M in the UK system.

Many of the laser pointers in the study were labelled incorrectly against any known classification system (UK, IEC/international, new US and old US)

Measured Power Levels and Laser Classification

Red lasers – power

Red Laser	Description	Advertised as:	Output Power mW	Correct Classification
1	Pen style pointer	1 mW	0.8 mW	Class 2
2	Aiming pointer	3 mW	7.8 mW	Class 3B
3	Small key-ring type pointer	1 mW	2.7 mW	Class 3R
4	Pen style pointer	1 mW	3.2 mW	Class 3R
5	Pen style pointer	1 mW	2.4 mW	Class 3R
6	Pen style pointer	1 mW	7.6 mW	Class 3B
7	Pen style pointer	1 mW	10.9 mW	Class 3B

Only one of the seven red laser pointers was less than 1 mW as advertised, and hence the Class 2 that was advertised. Three of the seven red laser pointers are Class 3B

Green lasers

Green Laser	Description (all pen style pointers)	Advertised as:	Output Power mW	Correct Classification
1	<5 mW Class IIIA label	1 mW	125	Class 3B
2	<1 mW Class CII label	1 mW	96	Class 3B
3	<1 mW Class II label	1 mW	215	Class 3B
4	<5 mW Class III label	1 mW	9.1	Class 3B
5	<1 mW	1 mW	56	Class 3B
6	<5 mW Class III label	1 mW	145	Class 3B
7	<5 mW Class III label	1 mW	83	Class 3B
8	<5 mW Class IIIb label	5 mW	137	Class 3B
9	<1 mW	1 mW	82	Class 3B
10	<5 mW Class III label	1 mW	59	Class 3B
11	<5 mW Class III label	1 mW	175	Class 3B

All eleven green (532 nm) laser pointers were found to be well into Class 3B, a class were direct exposure of the human eye to the laser beam is hazardous, with the potential for permanent retinal injuries.

The lowest power green laser tested appeared to be faulty, with intermittent operation and the odd brighter flash indicating that this laser might well be higher power if functioning correctly.

Only green laser 8 was labelled as IIIb, and this is an older US style label rather than a UK or international label.Many of the other lasers are labelled with classes of laser that do not actually exist, and can therefore be of limited use, particularly when they state power levels that bear no relation to the measured power output.

Blue lasers

Blue Laser	Description (all pen style pointers)	Advertised as:	Output Power mW	Correct Classification
1	<5mW Class III label	1 mW	10.7	Class 3B
2	<5mW Class III label	1 mW	18.6	Class 3B

These are one of the newest colours of laser pointer, with wavelengths at 405 nm which is only just in the visible spectrum. In consequence, these lasers appear less bright which can make users feel they are not as big a threat to the eye as they are.

Hazard Distances

The classification of lasers is based on the risk of injury.

Since laser output is typically in a narrow beam of light, the hazard can exist for a long distance along that beam. An important parameter in the risk assessment and management of lasers is the Nominal Ocular Hazard Distance (NOHD). This is the distance from the laser aperture within which direct intrabeam exposure of the eye would exceed the Maximum Permissible Exposure (MPE) level. Beyond the NOHD any exposure to the laser beam is normally regarded as being safe in that it will not result in any injury to a normal person.

Calculated hazard distances

Any Laser with of a class above Class 1, will have an NOHD greater than 100 mm, but the laser standard dictates that the NOHD is normally calculated for an exposure duration of 100 s, whereas for exposure to a visible laser pointer such an exposure duration would require deliberate effort. Exposure would most likely be a short duration, with the eyeball moving rather than remaining still. In order to indicate the potential for accidental injury, we have calculated the MPE for a 0.1 s exposure, and then used this limit to calculate the “0.1 s NOHD”. In other words this is the distance within which an expose of just 0.1 s to the direct beam from the laser could cause a retinal eye injury.

Red Lasers

Red Laser	Output Power mW	NOHD (100 s) /m	0.1 s NOHD /m
1	0.8	6.2	0
2	7.8	30	15
3	2.7	16.8	8
4	3.2	12.3	6
5	2.4	22.6	10
6	7.6	22.8	12
7	10.9	23.9	13

The 0.1 s exposure NOHD demonstrates that the Class 2 laser represents a reasonably low hazard for accidental exposure by producing an NOHD of 0 m.

Green Lasers

Green Laser	Output Power mW	NOHD (100 s) /m	0.1 s NOHD /m
1	125	139	77
2	95.6	136	75
3	215	114	63
4	9.1	108	57
5	55.7	75	41
6	145	168	93
7	83	92	51
8	137	163	90
9	82	92	50
10	58.5	94	52
11	175	247	137

Blue Lasers

Blue Laser	Output Power mW	NOHD (100 s) /m	0.1 s NOHD /m
1	10.7	192.5	31
2	18.6	509	85

 

Visual Interference Distances

There are other distances where hazards exist for other reasons. In the case of the exposure of aircraft pilots or car drivers, there is also a ‘dazzle’ hazard due to the temporary, possibly only momentary, loss of vision. A similar hazard could apply to any worker performing a critical task where temporary loss of vision or even distraction, could affect safety. In this circumstance the most appropriate standard would be the US ANSI Z136.6 standard as there is not yet a UK or international equivalent.

In particular, the ANSI Z136.6 standard defines visual interference limits for ‘flight zones’ depending on the potential hazard within each zone. The standard effectively takes account of the fact that during more safety critical stages of flight, such as landing, a distraction alone could prove hazardous, whereas during ‘normal flight’ a dazzling light level, whilst undesirable, may not be hazardous if its effects are only momentary.

Laser Beam Distances	Description	Irradiance limit
Nominal Ocular Hazard Distance (NOHD)	The beam is an eye hazard (irradiance above the MPE) from the laser source to this distance. Risk of eye injury. Beyond this distance the MPE is not exceeded.	Maximum Permissible Exposure (MPE)
Sensitive Zone Exposure Distance (SZED)	The beam is bright enough to cause temporary vision impairment from the source to this distance. Beyond this distance the beam irradiance is less than the SZED irradiance limit.	100 μW/cm 2
Critical Zone Exposure Distance (CZED)	The beam is bright enough to cause a distraction, interfering with critical task performance, from the source to this distance. Beyond this distance the beam irradiance is less than the CZED irradiance limit.	5 μW/cm 2
“Laser-Free” Exposure Distance (LFED)	The beam is dim enough that it is not expected to cause a distraction. Beyond this distance the beam irradiance is less than the LFED irradiance limit.	50 nW/cm 2

The Laser Free Zone, for example, is the area immediately above the airfield extending to a height of 2000 feet, where aircraft landing or taking-off could be at risk if the pilot is distracted, or worse panics, for even a brief time. Indeed any sudden bright light could be taken to be the navigation light of another aircraft on a collision course!

Similar principles can be applied to other tasks, most obviously driving a vehicle, where dazzling light levels could be hazardous, but also to some other workplace tasks. The visual interference zones are designed for exposure during periods of low ambient lighting, since the ability to produce ‘glare’ or ‘dazzle’ is highly dependent on the state of adaptation of the eye. For example car headlights that dazzle at night will not be a dazzle hazard in normal daylight conditions.

Visual Interference Distances for Green Lasers

The ‘dazzle’ distances for green lasers corresponding to the Sensitive Zone and the Critical Zone have been calculated for the green laser pointers as shown in the following table and plot. The distances for red and blue laser pointers are somewhat shorter as these lasers are far less visible to the human eye, whereas the 532 nm green lasers are much closer to the eye’s maximum sensitivity at around 555 nm.

Green Laser	Sensitive Zone Exposure Distance /m	Critical Zone Exposure Distance /m
1	442	1981
2	435	1949
3	475	2126
4	355	1601
5	241	1082
6	536	2401
7	294	1321
8	521	2334
9	293	1313
10	302	1355
11	785	3516

These values have not been corrected for the Photopic Luminous efficiency of the eye, or for atmospheric absorption and scattering effects (they are considered ‘vacuum distances’). These corrections will make only a small difference to the figures quoted above, but would, for example, yield SZ distances approximately 7 or 8% shorter than those quoted in the table above. In practice the corrections are not linear and so a simple percentage value can not be quoted for all values.

Conclusions

Of the 20 low-cost laser pointers tested, only one had a power of less than 1 mW as required for Class 2 laser pointers. 16 of the 20 laser pointers, including all of the green ones, had outputs above the 5 mW maximum level for Class 3R devices. All of the green laser pointers (except one that appeared faulty) had outputs above 50 mW, more than 10 times the Class 3R limit and more than 50 times the Class 2 power they were sold as.

In effect the attempts to limit the sale of high-power laser pointers to the general public appear to have resulted in a deliberate mis-labelling so these pointers can be sold without impairment. This selling and mis-labelling of hazardous, high power laser pointers as relatively safe Class 2 devices is a concern as many users are unlikely to realise the hazards posed by the device they are using.

Private users, who are unlikely to have any means of testing the devices, will likely have no idea that what is labelled as safe to use in classrooms, playing with cats and star watching, could in fact cause permanent eye injuries, or imprisonment for interference with flights. The low cost of these devices compounds the problem, as people simply do not expect to pay under £10 for a 1mW laser pointer and get one with 50-200 times higher power than they have paid for!

Companies who have to carry out risk assessments in order to comply with the new Artificial Optical Radiation Directive (AORD) could also be caught out, as very few will have the equipment to actually test lasers, rather than just trusting the label.

Of even wider ranging concern is the whole principle of manufacturers deliberately mislabelling devices with safety information rather than just designer logos. This study demonstrates that private and commercials consumers must be aware that safety labels can’t automatically be trusted, particularly when the supplier is not a known or reputable seller.

Link to a page discussing Laser Pointer control.