Lucent Technologies LambdaXtreme Alarm Messages And Trouble Clearing Manual page 22

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Lasers and Eye Damage
Light energy emitted by laser and high-radiance light-emitting diodes
(LEDs) in the 400 to 1400 nm range may cause eye damage if
absorbed by the retina. When a beam of light enters the eye, the eye
magnifies and focuses the energy, magnifying the irradiance. The
irradiance of the energy that reaches the retina is approximately 10
100,000 times that at the cornea, and if sufficiently intense, may cause
a retinal burn.
The damage mechanism at the wavelengths used in telecommunica-
tions is thermal in origin, for example, damage caused by heating.
Therefore, a specific amount of energy is required for a definite time
to heat an area of retinal tissue. Damage is not instantaneous. It
occurs only when one looks at the light sufficiently long enough that
the product of the retinal irradiance and the viewing time exceeds the
damage threshold. Light energies above 1400 nm would cause surface
and skin burns and do not affect the retina. The thresholds for injury
at wavelengths greater than 1400 nm are significantly higher than for
wavelengths in the retinal hazard region.
Classification of Lasers
Manufacturers of lasers and laser products in the United States are
regulated by the Food and Drug Administration's Center for Devices
and Radiological Health (FDA/CDRH) under 21 CFR 1040. These
regulations require manufacturers to certify each laser or laser product
as belonging to one of seven major Classes 1, 1M, 2, 2M, 3R, 3B,
and 4. The International Electro-technical Commission (IEC) is an
international standards body that writes laser safety standards under
IEC-60825. Classification schemes are similar with Classes divided
into Classes 1, 1M, 3R, 3B, and 4. Lasers are classified according to
the accessible emission limits and their potential for causing injury.
Lightwave systems are generally classified as Class 1, because, under
normal operating conditions, all energized laser transmitting circuit
packs are terminated on optical fibers which enclose the laser energy
with the fiber sheath forming a protective housing. Also, covers are in
place over the circuit pack shelves. The circuit packs themselves,
however, may be FDA/CDRH Class 1 or 3B, or IEC Class 1, 3R, or
3B.
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