Researchers report that green laser pointer's light is brighter to the eye than red lasers, but its infrared light emitted by some cheap models can damage the retina of the eye.
Charles Clark, PhD, of the National Institute of Standards and Technology (NIST), led a research team to measure the output of various green laser pen pointers.
The investigators bought three cheap laser green pointers, which were advertised to have a power of 10 mw.
Researchers say that one of the units sent dim green light, but infrared levels of almost 20 mw.
That's enough to cause damage to the retina before a person is even aware of the invisible light.
Tests of several other laser pointers found intense infrared emissions in some but not all, units.
According to a press release NIST, the problem is the result of inadequate procedures in the manufacturing process.
The problem can be solved by building a cheap infrared filter at the end of the laser that would significantly reduce infrared emissions.
These filters exist in the modern digital cameras and the more expensive green laser pointers, but they are often omitted from the cheap models.
Owners of green laser pointers should never be among them at anyone's eyes or focus them on windows, which can reflect infrared light back to the user.
The research is described in a publication called NIST Technical Note 1668.
NIST is part of the Ministry of Commerce.
While maintaining a healthy weight is associated with a reduced risk of cardiovascular disease and diabetes, overweight could even some women against a form of glaucoma, Harvard onderzoekers say.
This new finding suggests that overweight women have a lower risk of developing primary open-angle glaucoma (POAG), one of the most common age-related eye diseases.
In particular, overweight women may be especially protected against a variant of POAG called normal tension glaucoma, the researchers say.