Laser Safety Considerations for Laser Pointers
There are several considerations in order to ensure that laser pointers are used safely, particularly given that many laser pointers sold have power levels somewhat greater than the Class 2 maximum of 1 mW. This Class 2 is the maximum class of laser that the Health Protection Agency (HPA) in the UK recommends is acceptable to be sold to the general public.
In the UK the General Product Safety Regulations 2005 are sometimes used by the Trading Standards Authority to remove laser pointers of greater than Class 2 from sale to the general public, however dealing with many small internet purchases, particularly when they are mis-labelled, would be very difficult for any authority, and these products are readily available over the internet.
Eye (Retina) Hazard
Visible light is a hazard to the light sensitive retina at the back of the eye. An injury (burn) to this part of the eye can destroy some fo the light sensitive rods and cones such that the eye develops a blind spot. This type of injury is currently irreversible since the eye does not regenerate the rods and cones in the retina after injury. Depending on the location of the injury on the retina, the effects on eyesight can vary from being quite minor to extremely serious – even a small burn in the wrong place can drastically effect the sight in that eye!
Where the injury has caused a lesion, or bleeding in the eyeball, then this can heal and some improvement is eyesight will occur as the eyeball clears. It is however likely that some of the rods and cones will be destroyed.
People looking to purchase higher power laser pointers should consider that retinal eye injuries can be permanent.
Visibility (photopic response)
A key consideration for a laser pointer is that the light from the pointer is a visible wavelength, but not all wavelengths are seen equally by the human eye. The following table provides some visibilty data as a percentage of the human eye’s peak sensitivity at around 555 nm (green light) for an ‘average’ person.
|Violet 405 nm
|Blue 445 nm
|Green 532 nm
|Green 555 nm
|Red 632 nm
|Red 650 nm
|Red 675 nm
Clearly Blue lasers are not an ideal colour for laser pointers as they need to be of a much higher power in order to produce a spot of light appearing as bright as that from a lower power Green laser pointer. Users may consider the laser ‘not so powerful’ because it si not so bright, whilst in reality blue light can be more hazardous to the eye.
The greater visibility of Green laser pointers makes them a good bet for pointing out stars at night, but also means that they can be more of a threat in producting visual impairments – see below.
Visual Impairment Hazard:
Highly visible lasers such as many green laser pointers or extremely high power red and blue laser pointers can cause temporary blinding, particularly in dull ambient light conditions such as night time. The extent of the temporary blinding can vary depending on exposure from just for the duration of the exposure to lasting for second or in extreme cases minutes after the exposure.
When it is claimed that certain laser pointers can be deadly, it is generally this temporary visual impairment that can create the conditions for an aircraft pilot or car driver to have an accident. In effect the laser pointer is deadly due to it increasing the likelihood of a fatal accident from another activity.
For more details on the visual impairment hazard posed by laser pointers click here.
Laser Reflection Hazards:
There is a general belief that you can play with a powerful laser pointer and so long as you don’t look into it or point it at people then you and others will be safe. This is partly true, but higher power laser pointers can be a hazard to the eye over a significant distance, and the light can reflect of all manner or metal or smooth polished surfaces. Reflections can drastically alter the direction of a laser beam. When an injury can occur from only momentary exposure, the laser user must be very careful and aware of this issue.
Whilst some of the higher power laser pointers can cause skin burns, this is generally a slower process (it requires longer exposure) than eye injuries, and may therefore require both laser and skin to be still for some time (possibly seconds depending on the laser). Additionally, the skin is generally able to repair minor damage, so injuries are less serious.
With skin in particular, there is a wide range of exposures that might be hazardous depending on the part of the body and the colour of the skin. Some parts of the body have significantly thicker skin than others, as do some people, and darker skin colours are generally more sensitive to thermal burns from lasers, whereas fairer skin types are more at risk of photo-chemical (sunburn type) laser injuries that generally result from longer term exposure to lower power levels.
Setting Skin on Fire!
Claims that these laser pointers can set skin on fire are somewhat sensationalist. They imply flames, or at least a good dose of smoke from the skin almost instantaneously, but for this to happen the flesh would have to be dry. The reality is that a good deal of most people is water and to set the skin on fire would require the water in the flesh to be boiled away first. The reality is clearly that the skin will suffer a burn from a laser pointer long before there is any realistic possibility of flames developing!
Laser Hazard Distances
Because laser light from laser pointers is emitted in a narrow beam, the energy is concentrated into a small beam area, and it is this concentration of the light that makes lasers hazardous. What then makes them particularly hazardous is that the beam area from a laser pointer does not get much larger with distance, hence the hazard can be present at some distance from the laser pointer. This makes laser pointers quite different from many other hazards that people may be more familiar with.
Hazards from Laser Pointer Exposure at Long Distances
In the event of high power laser pointers, whilst the ‘power density’ does reduce with distance, there can still be more than enough power to damage the eye permanently, and the increased spot size can arguably result in a greater likelihood of accidental exposure being incident on the eye, and more specifically not just one but both eyes!
These considerations are provided for general information and lasers with Classes greater than Class 2 should ideally only be used by trained people who are responsible and aware of safety issues.