While green laser pointers deliver brighter light than their red cousins, a team of researchers at the National Institute of Standards and Technology (NIST) found that inexpensive versions of the green variety can produce excessive infrared light levels that could be dangerous to the user.
Late last year the NIST group purchased three low-cost green laser pointers advertised to have a power output of 10 milliwatts (mW). Subsequent measurements showed that one unit emitted dim green light but delivered infrared levels of nearly 20 mW—powerful enough to cause retinal damage to an unaware individual.
The NIST researchers repeated the tests with several other laser pointers (results can be found in NIST Technical Note 1668, July 2010) and found similarly intense infrared emissions in some but not all units.
The problem stems from inadequate procedures in manufacturing quality assurance, according to the research team. The NIST team says this problem could be solved by incorporating an inexpensive infrared filter at the end of the laser, which could reduce infrared emissions by 100-1000 times depending on quality and cost. Although these filters exist in modern digital cameras and more expensive green laser pointers, they often are left out of the inexpensive models.
To ensure safe use of laser pointers these devices should never be pointed at the eyes or aimed at surfaces such as windows, which can reflect infrared light back to the user—a particularly subtle hazard because many modern energy-saving windows have coatings designed specifically to reflect infrared energy.
