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Australia: Study shows inexpensive green laser pointers are mislabled and significantly over-powered
The researchers purchased eight laser pointers from sources including electronics stores and online stores. They bought four lasers with green beams and four with red beams. The cost of each laser was less than AUD $30 (USD $23).
All of the lasers were advertised to have a maximum output power of either less than 1 mW or less than 5 mW. The green laser pointers’ actual output power measured from 51 to 127 milliwatts. Dr. Fox said “At that upper level, the beam would cause catastrophic retinal damage.”
Apparently much of the green lasers’ power was in the infrared. These types of lasers work by generating non-visible infrared light which is then converted by a crystal into visible green light. A filter is normally used to block the infrared light, and only let the green light through. However, “[t]he research team found that imported laser pointers were poorly made, with manufacturers tempted to skip installing infrared-blocking filters to hold down costs.” The researchers did not measure how much of each lasers’ output was in the visible, and how much was in the infrared.
The 127 milliwatt green laser was labeled as a Class 2 device, with maximum output power of 1 mW. In a previous study from the U.S. NIST, the highest power output they measured was 66.5 mW from a green laser labeled as having a maximum output power of 5 mW.
Three of the four red laser pointers were found to be within the legal limit of 1 milliwatt. The fourth red pointer was about 8.5 milliwatts. The researchers felt that the red lasers’ spots were less focused than green lasers, meaning there was less risk of retinal damage. Also, red lasers use diodes. The maximum power output of these diodes is limited; excessive current will destroy the diode’s lasing capacity instead of providing a more powerful beam.
The researchers noted that “Our experiment raised two very pertinent concerns – first, why were class 3B lasers so easily purchased via the internet without licensing? This suggests that there are many loopholes in the importation of these products and more stringent processes need to be reinforced. Secondly, why did green lasers labeled as Class 2 reach up to a power output of 127mW, effectively attaining a class 3B classification? It is very likely that there is a significant infrared component. This drastic degree of non-compliance suggests that there needs to be more rigorous testing and quality control of these commercially available lasers – merely imposing a power limit of less than 1mW is insufficient.”
The researchers concluded by stating that “Authorities such as the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and medical authorities such as the Royal Australian and New Zealand College of Ophthalmologists (RANZCO) ought to advocate more strongly for stringent testing, quality control and licensing of green DPSS lasers.”
From an RMIT press release, “Over-the-counter laser pointers a threat to eyesight” and an advance copy of a paper, “Green lasers are beyond power limits mandated by safety standards,” which will be published in the Proceedings of the 2016 IEEE Engineers in Medicine and Biology Conference, online at the IEEE Xplore website. Thanks to Dr. Kate Fox for the paper.
The effort began when NIST physicist and laser safety officer Joshua Hadler worked with the U.S. Attorney’s office on a 2013 case in Fresno, California. Hadler already had devised a relatively simple and inexpensive way to accurately measure laser pointer powers. (His widely-reported study showed that a majority of pointers exceeded the U.S. limit of 5 milliwatts.)
But power is only one factor of the potential laser hazard. The beam spread, or divergence is another key factor. This is because a wide, high-divergence beam will have its energy spread out more, making it dimmer and less hazardous at a distance than an otherwise equivalent-power laser with a narrower, low-divergence beam.
To tackle this, Hadler used a pyroelectric laser camera to measure the laser’s divergence. From the power and divergence, and knowing the approximate distance to the aircraft from the Federal Aviation Administration incident reports, Hadler was able to calculate the irradiance, or laser power over a given area.
The information helped to get a conviction in the Fresno case. Hadler noted that in the past, “...the vast majority of prosecutions were failing, due in no small part to a basic lack of knowledge about the laser devices on the part of nearly everyone in the trial process, including lawyers, judges, and jury members. What they needed was to be able to acquire and present quantitative data about a device's power and its effects at a specified range that could be used in the judicial process."
Hadler will present a paper on February 21 2014 at the American Academy of Forensic Sciences meeting in Seattle, Washington. The paper, “Output Characterization of Handheld Lasers Used in Criminal Aircraft Illumination,” will discuss the needed measurements and will present ideas for having these measurements be done outside of NIST, in law enforcement forensic labs.
The findings were made public at a March 20 2013 meeting of the International Laser Safety Conference.
Researcher Joshua Hadler designed the measurement device to be accurate, inexpensive and easy-to-use. It would cost roughly $2000 in equipment costs to make a copy of the NIST device; plans are available from NIST for interested parties.
From a NIST press release, March 20 2013.
Click here for the full press release:Click to read more...
The NIST team came up with a simple “home test” so that interested persons can test their own laser pointers. The test requires a digital or cellphone camera, a compact disc used to spread out the wavelengths, a webcam to view infrared light, and an infrared TV remote control.
At top, light from a green laser pointer is diffracted (spread out) by a compact disc and viewed with a digital camera that can see only visible light. At bottom, a webcam with no infrared-blocking filter shows this laser also emits infrared laser light (white dots). For this unit, the invisible infrared light is more powerful than the visible green light. (NIST photo)
The unwanted and potentially hazardous infrared light is due to misaligned or missing filters in laser pointers that use infrared to generate visible green light. Low-cost pointers are at special risk, due to cutting corners in design, materials or manufacture to reduce costs.
The team warns that, whether or not a laser pointer emits dangerous levels of infrared, users should “never point the lasers at the eyes or aim them at surfaces such as windows which can reflect infrared light [as well as visible light] back to the user” or others in the area.
For more information:
- NIST press release summarizing the issue
- NIST technical note A Green Laser Pointer Hazard which includes instructions on how to test to see if a green laser pointer has unwanted or excess infrared light emission (PDF format)
UPDATE - March 2011: A laser expert has privately warned LaserPointerSafety.com that the CD technique requires caution. This is because when the laser light is diffracted, the infrared light is no longer co-linear (same path) as the visible light. Therefore, the viewer cannot know exactly where the IR light is going unless they are looking through an IR-sensitive camera or webcam.