The New Straits Times, November 2, 1998
First developed in 1960, the laser, an acronym for light amplification stimulated emission of radiation, has become a common device in industry, commerce, entertainment and medicine.
Laser pointers - the hand-held, pen-like devices that project a beam of laser night - are rapidly replacing the traditional wooden pointers used by lecturers during presentations.
However, these pointers can be misused, for example, by students in classrooms or by children at home, and this has generated safety concerns. There have been reports of temporary blindness, disorientation and headaches by bus drivers, airline pilots, police and teachers.
Manufacturers are now using similar low-powered laser devices in toys.
Two questions have been raised: should these products be available to the general public and how dangerous are they?
A recent World Health Organisation Fact Street (no. 202) provides information about the properties of laser radiation and different laser classes and summarises WHO's advice on the safe use of laser pointers.
Lasers produce radiation, more commonly referred to as light with unique properties that distinguish laser-produced light from light produced by more familiar sources such as the sun or common domestic lamps.
Domestic lamps emit light that is highly divergent, i.e. it spreads out almost equally in all directions from the lamp. This light has many different wavelengths (colours), which together give the characteristic colour of the lamp.
In contrast, a laser produces light in a very narrow wavelength band, so narrow that the laser is referred to as a monochromatic (one colour), or single wavelength, source. Lasers can also produce a very narrow beam that diverges little. This low divergence means that laser light is highly directional, forming a pencil-like beam and appears as a small spot when projected onto a surface, even at distances of hundreds of metres.
As a consequence, high power lasers can be hazardous to the eye over considerable distances. Because laser light is monochromatic and basically low-divergent, the beam is better focused by the lens of the eye than any other light source, thus producing images on the retina with much greater intensities than is possible with domestic lamps.
It appears that the output power of laser pointers currently available is generally less than 5mW. Although the risk of permanent eye injury from laser pointers may be small, a person receiving even a transient eye exposure will experience a bright flash, a dazzling effect which is likely to cause distraction and temporary loss of vision in the affected eye and possibly after-images.
The time taken to recover from these effects will vary for different people and will also be dependent on the ambient light level at the time of exposure. Medical attention should only be sought if after images persist for hours, or if a disturbance in reading vision is apparent.
Normally, laser pointers are classified as Class 1, Class 2 or Class 3B products reflecting an increasing output power that can cause more serious eye injury. However, national authorities making measurements of the power output of these lasers have noted that significant misclassification is occurring among manufacturers.
In many cases, lasers had been classified as Class 2 when they were really Class 3B.
Safety standards and classification of laser pointers
Laser pointers are classified according to the International Electrotechnical Commission (IEC) standard on laser safety. This standard specifies requirements for the laser to ensure that the risk of accidental exposure is minimised through the use of engineering control features and that there is product labelling and safety information.
The IEC also sets out five classes of laser - 1, 2, 3A, 3B and 4. This classification gives the user an indication of the degree of laser hazard.
Class 1 lasers have an output power that is below the output power of 1mW at which eye injury can occur.
Class 2 lasers emit visible light and are limited to a maximum output power of 1mW. A person receiving an eye exposure from a Class 2 laser will be protected from injury by his/her natural blink reflex, an involuntary response that causes the person to blink and turn his/her head, thereby avoiding eye exposure.
Class 3A lasers may have a maximum output power of 5mW. This limit restricts the power entering a fully dilated human eye (taken as 7mm aperture) to 1 mW. Thus, accidental exposure to a Class 3A laser should be no more hazardous than exposure to a Class 2 laser. However, Class 3A laser pointers are hazardous when viewed with an optical aid such as binoculars and are therefore not suitable for the general consumer.
Class 3B lasers have an output power up to 500mW, sufficient to cause eye injury. The extent and severity of any eye injury will depend on several factors including the laser power entering the eye and duration of exposure. Class 1, Class 2, Class 3A and Class 3B lasers do not have sufficient power to cause skin injury.
Class 4 lasers have an output power greater than 500mW and are capable of causing injury to both the eye and skin and will also be a fire hazard if sufficiently high output power is used.
The IEC provides advice on the use of the lasers for demonstrations, displays and exhibitions and states that only Class 1 or Class 2 devices should be used in unsupervised areas unless under the control of experienced well-trained operators.
Laser pointers used by, for example, professional lecturers in the workplace are considered to fall within this category. Training requirements are specified for operators using lasers of higher class for these purposes, as there is a risk of eye injury.
In the United States, a different laser classification exists for low-powered devices. A Class 3A laser classified by the IEC standard, and having powers up to 5mW, is classified as IIIA in the American standard. The use of Roman numerals should indicate that the laser has been classified according to the American standard. In practice, examples have occurred where an inappropriate 3A label has been substituted for the IIIA label.
WHO considers the professional use of a Class 1 or 2 laser pointer as a training aid to be justified and regards these classes of laser products as being adequate for such use. The use of Class 3B laser pointers may be justified for some applications in the workplace where the user has received adequate training.
There has been significant concern, however, that laser pointers are being used in children's toys. Lasers in toys should be restricted to Class 1, and Class 2 laser pointers should not be sold to children.
In general, the sale of laser products to the public should be restricted to Class 1 or 2 devices and should be sold with sufficient accompanying information to enable the user to operate the products in a safe manner. Laser pointers higher than Class 2 are considered too powerful for general use and present an unacceptable risk as they may cause eye injury.
