The seemingly harmless laser pen has turned out to be a threat to flight safety after pilots expressed concerns about growing incidents of laser lights being flashed at planes flying in and out of Changi Airport.

Between January and March, the Civil Aviation Authority of Singapore (CAAS) received 16 reports of laser lights being flashed here, compared with 25 for the whole of last year. The CAAS has launched a public awareness campaign, targeting households in the east.

Here's a Q&A about laser pointers:

What are the different types of laser pointers?

Low-powered laser pens and pointers commonly used in presentations can be bought off-the-shelf in most stationery stores in Singapore. These pointers usually emit red light and usually cost around $20. There are more expensive ones that emit green or blue light which can cost more than $100.

The use of lasers comes under the Radiation Protection Act, administered by the National Environment Agency (NEA). Power output of laser pointers is measured in milliwatts (mW), and they come under different classes - from 1 to 4, with 1 being the lowest - based on how powerful they are. One milliwatt is equal to one thousandth of a watt.

Red laser pointers usually come under Class 1, 2 or 3A, with a power output of up to 5 mW. All class 3B and 4 laser apparatus, including laser pointers, are considered controlled items under Singapore rules. Owners and operators are required to have the necessary licences in order to legally possess and/or use these apparatus.

Is it true that laser pointers can be dangerous?

Yes, if they are not handled properly. This is because the eye can focus a laser beam to a very small, intense spot on its retina, which can result in a burn or blind spot.

Even at a very low power of 5mW, a laser pointer - if aimed directly at the eye - can cause temporary flash blindness. A split second brief exposure from such lasers is not likely to cause permanent injury immediately because the eye will blink and move to avoid the beam, but it can lead to visual loss in later years.

Can a laser beam reach a plane so far away?

Yes, even a low-powered laser pointer can be a distraction to aircraft at a distance of 2 miles, or about 10,560 ft.

For instance, a 5mW laser beam can be a distraction hazard to a pilot flying an aircraft at an altitude of about 11,700 ft. It can cause glare at an altitude of about 1,170 ft; temporary flash blindness at 262 ft and eye damage at 52 ft.

The beam, which may be just a millimetre-sized dot close up, is also much larger at long distances. Hence, this could affect flight safety, especially during the crucial stages of take-off and landing.

Is a green laser pointer more dangerous than a red one?

It really depends on the power output. But green laser pointers can be more dangerous in the sense that they fire off a considerable amount of infra-red signal in addition to visible light. The human eye is far less sensitive to infra-red, which means it can't protect itself by avoiding it.

Who uses laser pointers?

Besides those doing presentations, some astronomy enthusiasts use laser pointers for "star pointing" and for "drawing out" a constellation.

There are also laser hobbyists who make laser pointers the D.I.Y way, or study how to make these pointers more powerful.

Another group which is causing concern in some countries is the so-called laser pranksters. They aim laser pointers at buildings, aircraft, people and even football players in the field. For example, Olympique Lyon was fined 5,000 Swiss francs (S$7,146) after the French club's supporters used a laser to target Cristiano Ronaldo from the opposing team during a match in 2008.

Do other countries face the same problem?

Several countries have expressed concern over laser incidents which have resulted in cases of pilots suffering from burnt corneas.

In the United States, the number of aviation-related laser incidents hit an all-time high of 3,960 last year, from 283 in 2005. Cities with the most number of laser hits include Houston, Phoenix and Los Angeles, and Portland, Oregon.

The Federal Bureau of Investigation is offering reward money for tips leading to laser pranksters. It has detained mostly teenage boys and men in their 30s, who face a possible five years in prison and a US$250,000 (S$313,913) fine, reported CNN.

In February 2011, a 14-year-old boy was arrested for shining a laser pointer at an aircraft on approach to Los Angeles International Airport. In March last year, a 19-year-old man in California was sentenced to 30 months in jail for shining a laser pointer at a plane and police helicopter.

In Australia, the authorities have banned the import of laser apparatus that emit a beam stronger than 1 mW, citing a series of coordinated attacks on passenger jets in Sydney.

What are some safety measures you can take?

- Avoid looking directly into the laser beam of your laser or pointing the beam at any other person or animals. Note that not all laser beams are visible to the naked eye.

- Do not point the laser beam at mirror-like surfaces.

- Do not view a laser beam using optical instruments, such as binoculars.

- If you are using laser pointers for star pointing, do not point directly at a dim or unknown "star" which may be an aircraft. Instead, move in a circular motion around the object. When "drawing out" a constellation, keep the beam moving and keep it away from any stars.

Source: NEA, www.laserpointersafety.com