MadSci Network: Physics

Re: Will the red light on a bar code scanner injure your eyes?

Date: Thu Oct 5 11:05:08 2000
Posted By: Kelly Dennison, Staff, Environmental Science/Industrial Hygiene, Earth Tech
Area of science: Physics
ID: 970677645.Ph

A bar code scanner, known as a POS, or point-of-sale scanner uses a laser 
to read the bar codes found on most every item available for purchase or 
for use in inventory.

A laser is an acronym for light amplification by stimulated emission of 
radiation.  It produces non-ionizing radiation in the form of light.  They 
pump electrons through a specific material and with energy and direction, 
emit a red beam of concentrated light.  This light beam, or wavelength, is 
measured in nanometers (nm) and is usually found in the visible range (400 
nm -760 nm).  By contrast, ultraviolet light (such as a black light) is 
315-400 nm.  

Lasers are classified hazardous by the power they are activated at and the 
wavelentth they are run at.  Lasers can be classified from Class 1 (non-
hazardous) to Class 4 (very dangerous).  Class 4 lasers are usually used 
by the military and in medical research.  POS lasers run somewhere in the 
vicinity of 650-675 nm in the visible light range and are operated with 
approximately 1 watt of power.

According to the American National Standards Institute (ANSI) Z136.1-1993, 
the POS laser is a Class 2a laser, meaning that it is not hazardous unless 
it is viewed directly for up to 1000 seconds (or 16.7 minutes).  This type 
of laser if viewed for this long would cause retinal burns, which may not 
be apparent for several hours after exposure. 

Since the bar code scanners are meant for only scanning bar codes and not 
for human viewing, there are no safety factors built in.  The user should 
be aware of the hazards of viewing the beam directly, and should use the 
item in the manner it was meant to be used.

I hope this answers your question!  

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