The Specturm of Light
The sun is a source of electromagnetic energy including
radio waves, infrared, visible light, ultraviolet, x-rays, gamma rays,
and cosmic rays. Each band has its own characteristic wavelengths and
properties as a result of wavelength.
Visible light is "visible" because its wavelengths can be
detected as various colors by the human eye. Ultraviolet, although invisible,
also has various wavelengths and properties.
Learm more about the UV Specturm. |
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UV-A, UV-B, and UV-C are part of the ultraviolet spectrum and we are usually exposed to some of each every day. UV exposure can be harmful or harmless depending on the type of UV, the type of exposure, the exposure duration, and individual differences in response to UV.
Is ultraviolet light harmful?
The difference has to do with the ability
of UV rays to penetrate body surfaces.
UV-A is also known as "blacklight" and
is generally harmless. It results in skin tanning and is used in
medicine to treat certain skin disorders.
UV-B has a very high
penetrating ability and prolonged exposure is responsible for some
types of skin cancer, skin aging, and cataracts (clouding of the
lens of the eye).
UV-C has extremely low penetrating
ability and is nearly completely absorbed by the outer, dead layer
of skin where it does little harm. It does reach the most superficial
layer of the eye where overexposure can cause redddening and painful
but temporary irritation, but it cannot penetrate to the lens of
the eye and cannot cause cataracts. UV-C is also known as "germicidal
UV."
Germicidal UV
Germicidal UV has a specific wavelength of 253.7 nanometers (253.7 billionths
of a meter) and is known to deactivate (break the DNA of) germs contained
in tiny airborne droplets (droplet nuclei) that transmit diseases such
as measles, tuberculosis, and influenza from person to person.
Once the DNA of a microbe is broken it loses its ability to reproduce.
Bacteria and viruses that can not reproduce are rendered harmless.
Germicidal
UV has been used safely and effectively in hospitals, clinics, laboratories,
and industry for more than 50 years. |
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Improvements in the technology
Electric lamps, resembling ordinary flourescent lamps, are especially
designed to emit germicidal UV and include a glass envelope to filter out
harmful, ozone forming radiation. The lamps are available in a variety
of sizes and shapes and must be mounted in special housings and located
so that people are not exposed to direct irradiation.
The newer, compact
tubes are technologically more advanced and provide higher UV-C output
and increased reliability. The shorter tubes also permit a variety of
special application fixture designs to maximize UV-C in a room by mounting
the units from the ceiling, from walls, and in corners and corridors.
Lumalier features a complete line of application specific fixtures using
the newer, more effective, compact lamps. |
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Installation
Fixtures for upper room air irradiation provide a high
intensity beam of germicidal UV while shielding the lower part of the
room. Highly reflective parabolic reflectors and louvers focus the rays
into a wide but narrow zone while minimizing energy loss and stray irradiation.
The shape and placement of the louvers is critical.
Underneath the zone, where the people are, the National Institute for
Occupational Safety and Health (NIOSH) recommends that the UV-C intensity
should not exceed 0.2µw/cm2 below the six foot level. The recommendation
is based on eight hours continuous exposure of the eye, the body's most
sensitive tissue, and includes a margin of safety. |
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Air mixing is the key
Air mixing is vitally important to provide disinfection of total
room air. Normal convection between upper and lower room air may
be adequate to move total room air and its airborne microorganisms
through the zone. However, if normal convection is not sufficient,
it should be supplemented with some method of forced air.
People spread germs
Anywhere people congregate there is a risk that an infected person
will exhale droplet nuclei carrying disease. Since the droplets
are very small (about 2,000,000 would fit on the head of a pin)
they can hang suspended or be carried on air currents. The infection
can then be dispersed throughout confined environments such as
buildings as the infected person moves about. Other people then
inhale the airborne droplets and contract the disease. Germicidal
UV should be installed throughout buildings where a significant
hazard of airborne infection has been identified. Hospitals, clinics,
prisons, treatment centers, and similar institutions are especially
susceptible. |
