Safety Laser Diode Pointer

The use of laser diode pointers that operate in the visible radiation region (400 to 760 nanometers [nm]) is becoming widespread. These pointers are intended for use by educators while presenting talks in the classroom or at conventions and meetings. They are also useful in any situation where one needs to point out special items during any instructive situation. The pointers can be purchased in novelty stores, mail-order magazines, office supply stores, common electronics stores, and over the Internet. The power emitted by these laser pointers ranges from 1 to 5 milliwatts (mW).

Many of these devices are low cost, operated with AAA batteries, produce a beam that can be seen easily hundreds of meters away yet are small enough to be carried in the pocket or on a key chain. One design is available where the laser pointer is co-housed with a functional writing pen. Pointers are now being manufactured that can project patterns of a star, circle, square, as-well-as the conventional circular dot pattern. Although most of these devices contain warning labels, as required by FDA regulations, many have been erroneously advertised as "safe". At present there are no limitations on purchases and anyone can now buy a laser pointer that could be potentially hazardous if handled carelessly. The number in use today easily number in the millions.

The potential for hazard with laser pointers is generally considered to be limited to the unprotected eyes of individuals who might be exposed by a direct beam (intrabeam viewing). No skin hazard usually exists. The natural aversion response or blink reflex of the eye to a bright light (t=0.25 s) would usually limit the intrabeam exposure to a safe level for devices emitting at Class II levels (ANSI Z136.1 Standard "For the Safe Use of Lasers" [1] would, however, suggest that an intentional intrabeam exposure with a 5mW visible diode laser could require an eye filter of Optical Density (OD) of 0.7 for exposures in the order of 0.25 s. Longer exposure would require higher OD's. Diffuse viewing conditions would need no eye protection.

There are, however, even more powerful laser pointers now appearing. The units are imported into the USA often without a proper manufacturer certification or labeling. One such pointer (reportedly imported from Russia) emits a green beam from a diode-pumped frequency-doubled Nd:YAG laser operating at 532 nm. The beam is the envelope of a series of 40 ns pulses of 0.5 J/pulse energy emitted at approximately 1.7 KHz. This equates to an average power of about 0.85 mW. This pointer emission is a factor of 12 times higher per pulse than the MPE limit allowed by the ANSI Z136 Standard - and therefore, this type of pointer presents a significant potential for an eye hazard if viewed directly!

Another diode-pumped frequency-doubled Nd:YAG laser operating at 532 nm is imported from China and emits 5 mW in a CW beam as detailed in the data given in Appendix A. The pointer has no labeling and unscrewing the front end cap removes the 1064 nm blocking filter. In this case, the combined 1064 nm and 532 nm beams exceed 15 mW; clearly a Class IIIB emission. This design does not meet FDA criteria for a Class IIIA laser pointer.

Other concerns with these low power laser include ocular effects such as flash-blindness, afterimage, and glare. Persons exposed to the beams from pointers can be subject to such effects which could lead to temporary vision dysfunction and cause possible physical dangers if the exposed person is engaged in a vision-critical activity such as driving, flying or operating machinery.

The potential for hazards with these devices is not well understood by the general public and numerous exposure incidents have been recorded by the authors [2]. Users of these products need to be alerted to the potential hazards and be encouraged to follow appropriated safety recommendations. These factors will be discussed and safety recommendations for laser pointers will be presented

LASER POINTERS: CLASSES, DEFINITIONS AND CONCERNS

Laser pointers are today, usually Class IIIA (1-5 mW) devices as defined by the ANSI Z136.1 standards. Class IIIA lasers are moderate power lasers which could be hazardous even if viewed for a very short time. Until about 1993, most pointers were Class II ( The FDA would include laser pointers under the definition of a demonstration laser product which is included in the U.S. Federal Laser Product Performance Standard: 21 CFR Part 1040.11 in the definitions for a Specific Purpose Laser Products [3]. That section indicates:

Demonstration Laser Products: Each demonstration laser product shall comply with all of the applicable requirements of 1040.10 for a Class I, IIa, II, or IIIa laser product and shall not permit human access to laser radiation in excess of the accessible emission limits of Class I and, if applicable, Class IIa, Class II, or Class IIIa.

Hence, by this definition, laser pointers are technically limited to a Class IIIa (5 mW) outputs. The detailed specification of one 5mW laser pointer device is given in Appendix B.

SAFETY ISSUES AND LASER BIOEFFECTS:

Concerns for the eye: Retinal Burns

The endpoint of various research studies determined the lowest laser eye exposure level needed to cause a "minimal" retinal lesion ("burn") using an ophthalmoscope to view the damage effects. Maximum Permissible Exposures (MPEs) were established in the late 1970's by the Z136 Committee of the American National Standards Institute (ANSI) "about a factor of ten" below the eye damage threshold level. It should be stressed that a retinal burn is unlikely result from a laser pointer exposure. Recently, a group of distinguished scientists and physicians warned that light induced damage was often mistakenly blamed for a patient's visual problems when, in reality, other causes were frequently a more likely cause [4].

The major potential hazard from pointers is limited to the unprotected eyes of individuals who look at the direct beam emitted from the laser since no skin hazard usually exists. The natural aversion response or blink reflex (~0.25 sec.) of the eye from the bright laser light normally limits exposure to a safe level for those devices.

The ANSI Z136.1 Standard bases the "blink reflex" MPE on an exposure on 0.25 second exposure. This yields an MPE of 2.5 mW/cm2. When this irradiance is spread over a "worst case" 7mm pupil opening (0.4 cm2), the total power entering the eye can be then computed as follows: Power = (2.5 mW/cm2) x (0.4 cm2) = 1.0 mW. This suggests that laser pointer type devices might be limited to an output of 1 mW (Class II).

In some darkly lit environments, and at some wavelengths, a 1 mW pointer power is perhaps an option, but in rooms with a high ambient light level and if operation is at the longer 670 nm wavelength, 1 mW is just marginal for visibility and, therefore, 3-5 mW is generally required for better visibility. Note that if the exposure is raised to a maximum of 5 mW (Class IIIA), then an eye filter with an optical density of 0.7 would be required for protection in the event of an intrabeam exposure of 0.25 seconds. This suggests that caution is needed when the pointer emits near the 5 mW power level!

WAVELENGTH CONCERNS

An evaluation of various laser pointers by the authors suggests that one needs to examine the photopic response curve of the eye (Figure 1) to better understand the laser pointer visibility factors: That data suggests:

Pointers at 670 nm emit a "dark red" - and require 3-5 mW (Class IIIA) in order to be to be "visible"

Pointers at 635 nm emit a "brighter orange" - and require only about 1 mW (Class II) to be "visible"

Some new "pointers" are diode pumped - frequency doubled Nd:YAG lasers that emit at 532 nm and emit in the power range of 5 mW AND HIGHER! Note the eye response is much higher at this wavelength.
Some may argue that the more recently purchased laser pointers do not pose as much of an occupational or consumer risk as the earlier laser pointers because the wavelength has been shifted from the "original" 670 nm (dark red) to the "new" 635 nm ("bright" orange-red). [Figure 1 illustrates this fact] In this case, the older 670 nm pointers usually emitted a radiant power ranging from 3 to 5 mW (Class IIIA), while the new 635 nm pointers often emit less than 1.0 mW (Class II) and are perceived as "brighter". It is concluded that the 635 nm pointers will not be as great a concern if one is pointed at someone's eye because of the lower power rating.

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