Chemical Education Today

30 Journal of Chemical Education • Vol. 80 No. 1 January 2003 • JChemEd.chem.wisc.edu

Letters

Take Care When Using That LaserPointer

In the experimental procedure of the Tested Demonstra-tion, “The Use of an Inexpensive Laser Pointer To PerformQualitative and Semiquantitative Laser Refractometry” (1),the authors give the following warning: “Avoid looking di-rectly at the laser beam.” This warning is insufficient.

A year ago I was working in the lab trying to test for thepresence of CO2 by bubbling a gas mixture supposedly con-taining this gas into limewater. Since the precipitate producedwas extremely scarce (it looked more like a colloidal suspen-sion), I thought of using a laser pointer to take advantage ofthe Tyndall effect and thus visualize it. I was using a conical-bottom vial (Ace Glass) and a commercial laser pointer. Af-ter using the laser for this purpose for a few minutes, andeven though I never looked at it directly, I realized that per-haps the reflections and refractions from the vial had some-what hurt my vision. For the next few days, I was very oftenseeing large “white spots” and this so worried me that I wentto see an ophthalmologist. After careful examination, he saidthat nothing of consequence had happened to my vision. Un-fortunately, my retina became very sensitive to bright lightfor several months. I have recovered, but I wanted to warnusers of laser pointers for purposes such as those mentionedabove, that in spite of not looking directly at the laser light,some side effects may derive from inadvertent reflections andrefractions at glassy or other materials.

Literature Cited

1. Neder, A. F.; García, E.; Viana, L. N. J. Chem. Educ. 2001,78, 1481–1483.

Jorge G. IbanezCentro Mexicano de Quimica en MicroescalaDepartamento de CienciasUniversidad IberoamericanaProlongacion Paseo de la Reforma 880Delegacion Alvaro Obregon01210 Mexico, D.F., Mexicojorge.ibanez@uia.mx

The Tested Demonstrations Editor replies:

The concerns expressed by Jorge G. Ibanez are real, ac-cording to an apparently authoritative and very informativeessay, “Safety Recommendations of Laser Pointers” by R. J.Rockwell, Jr., W. J. Ertle, and C. Eugene Moss, available onthe Web (1). This article notes that Class IIIA laser pointersare available in the U.S., even though they are banned in theUK. These lasers may be hazardous even if viewed for a veryshort time, and little research has been done on the chronicexposures like those reported by Ibanez. Lasers are classifiedfrom I (least dangerous) to IV, which requires strict controlmeasures. Up to class II are allowed as laser pointers in theUK. According to the Laser Institute of America cited byMetrologic (2), a Class II laser is defined as follows:

A Class II laser or laser system must emit a visible laserbeam. Because of its brightness, Class II laser light willbe too dazzling to stare into for extended periods. Mo-mentary viewing is not considered hazardous since theupper radiant power limit on this type of device is lessthan the MPE (Maximum Permissible Exposure) formomentary exposure of 0.25 second or less. Intentionalextended viewing, however, is considered hazardous.

Literature Cited

1. Rockwell Laser Industries: Safety Recommendations. http://www.rli.com/resources/pointer.asp (accessed Oct 2002).

2. Metrologic Instruments Inc. http://www.metrologic.com/corpo-rate/techfaq.htm (accessed Oct 2002).

Ed VitzDepartment of ChemistryKutztown UniversityKutztown, PA 19530vitz@kutztown.edu