Laser Pointers and Astronomy

Green laser pointers are useful astronomical tools. On public astronomy nights, the narrow beam from the laser pointer can be used to unambiguously point to celestial objects. The beam is bright and clearly visible for several reasons:

  • typical green laser pointers deliver at least 5 milliwatts (mW) of power
  • green light is scattered away from the beam direction by air molecules and dust particles (so you can see the beam from the side)
  • the eye is particularly sensitive to the green colour of the laser pointer.

Under the South Australian Summary Offences Act 1953, hand held laser pointers with an output greater than 1 milliwatt are prohibited weapons. This Guideline has been prepared to assist ASSA members using laser pointers to understand the changes to the use of laser pointers and is provided for information only and should not be regarded as legal advice.

Note: It is the responsibility of any person using a laser pointer to confirm that their use or possession is permitted by the relevant part of the Act. The Astronomical Society of South Australia makes no warrant as to the legality of any use of a laser pointer in South Australia. If using a laser pointer in other States, astronomers are recommended to seek local advice before operating a laser pointer.

South Australian Legislation

The South Australian legislation is typical of the state based legislation dealing with laser pointers. It applies to any hand-held laser pointer >1mW regardless of the wavelength of the beam. 

The legislation provides exemptions for persons in the course of conducting his or her business or for the purpose of or in the course of his or her employment plus for members of astronomical societies engaged in Astronomy. 

The legislation specifically recognises members of the Astronomical Society of South Australia as a class of people exempt from the prohibition but only when using a laser pointer for astronomy. The legislation deals harshly with people, including astronomers that misuse a laser pointer to endanger life or cause injury. 

What are the dangers of Laser Pointers?

Laser light from laser pointers can potentially burn the retina of the human eye. The danger is obviously greatest if the beam is aimed directly into the eye, rather than merely scattered from the beam and seen from the side. The danger is dependent on the wavelength of the laser light, the power of the laser pointer, the divergence of the laser beam, the distance of the person from the pointer, whether the beam is seen directly or via a reflection, how long the beam is viewed and whether the human eye's natural 'blink response' to bright light occurs.

The risk from a laser pointer is often also expressed by the 'class' of the laser pointer, although the definition is a little complicated and class definitions have changed in recent years. At one end of the scale, Class 1 laser pointers are safe for normal viewing.  Eye damage from directly viewing the beam of a Class 2 laser pointer is usually avoided by the blink response. Class 3 laser pointers can damage an eye before it has time to blink and have the potential to cause eye injury, especially in the hands of a careless or untrained operator. Class 4 lasers are even more dangerous, higher power devices.

The blink response should protect the human eye at any distance from any visible-light laser pointer beam with a power under 1 mW, typical of a Class 2 laser pointer. For laser pointers that are more powerful a greater distance is required to allow for blink response protection. For a given laser pointer beam, a quantity called the Nominal Ocular Hazard Distance (NOHD) can be calculated. Serious eye damage is probable within the NOHD and less likely at greater distances. The NOHD depends on the power, wavelength, divergence and diameter of the beam and the length of time the laser pointer beam will be viewed. For example, a 10 mW, collimated, continuous wave, green (532 nm) laser pointer beam with a diameter of 1 mm and divergence of 10-3 radian, being viewed directly for 10 seconds has a NOHD of 55 m. Clearly, this laser pointer, typical of many green laser pointers, is a potential hazard to someone close to it and should be used with care.

Damage to the eyesight of a pilot or driver is unlikely from medium power (5 mW to 20 mW) laser pointers given that the typical distances involved are considerably greater than the relevant NOHD. However, the dazzle caused by the beam scattering off dust or scratches on a windscreen, or the blink response itself could still lead to loss of control of a vehicle. A laser pointer beam could also potentially cause harm in other situations, for example by startling someone using a power tool.

Some amateur astronomers and small observatories have similar laser pointers permanently fixed to telescopes, although not always in use. While technically not hand held laser pointers, they should be used with similar safety guidelines in mind. 

Safety Guidelines

It is the view of the ASSA that the safe use of hand-held battery-operated laser pointers is possible in Astronomy by following the guidelines presented below:

  1. A laser pointer must only be used in accordance with the laws of the state or territory in which it is used.
  2. A laser pointer should be carried between observing sites deactivated [batteries removed].
  3. Laser pointers used for astronomy must require a button to be held continuously to activate the beam. If the laser pointer is dropped, the beam will automatically switch off.
  4. Before activating any laser pointer, astronomers must always check where people are located and ensure the beam is never directed in those directions.
  5. Always hold laser pointers overhead in an outstretched arm before activating the switch and release the switch before lowering the pointer.
  6. Never use a laser pointer to point out terrestrial objects. Aim the beam only at celestial objects. Do not aim the beam at any object on the ground, nor at aircraft, motor vehicles, any person or any animal.
  7. When the laser pointer is not being used to point at celestial objects return it to its case, place it in a pocket or cover the aperture from which the beam is emitted.
  8. Always cease using a laser pointer if an aircraft is heard and do not switch back on until the aircraft is clearly located and its flight path is confirmed to be well away from the patch of sky being identified with the laser pointer.
  9. Store the pointer deactivated in a secure place away from the reach of children and anyone with a potential to misuse the device.

To assist the police or other enforcement Agencies, astronomers must carry evidence of their current membership of an astronomical society at all times when the laser pointer is in their possession.