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The ABCs Of UV Light
By Barb
Checket-Hanks / Service/Maintenance and Troubleshooting Editor. Portions of an
article written by Barb Checket-Hanks. E-mail her at barbarachecket-hanks@achrnews.com.
For many contractors and
service techs, ultraviolet (UV) lights have become a much more common system
accessory. They have certainly piqued the interest of residential and commercial
consumers.
Most of these people do some
preliminary searching online when they are looking into indoor air quality (IAQ)
solutions. When they find information on UV lights, they will come across what
may be unfamiliar scientific terminology — nanometers, UVV, UVC, and the light
spectrum. They may find some basic information on UVC, but there isn’t much
out there about UVV, and UVV is one of the best weapons in the arsenal against
poor IAQ.
So, before the customer’s
nerdy kid shows up both his own parents and you, here are the basics of UV light
— the science, the technology, UVV, and some facts from the National
Aeronautics and Space Administration (NASA).
The Light Spectrum
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UV is part of the light
spectrum. According to NASA, the full spectrum includes radio waves, infrared,
visible light, UV, X-rays, gamma rays, and cosmic rays.
Let’s take a trip down
memory lane. Remember the light prism on the cover of Pink Floyd’s “Dark
Side of the Moon” album? When white light goes through a prism, it is broken
down into its component colors. (See Figure 1.)
Visible (white) light is
made up of colors that range from violet, to blue, to green, to yellow, to
orange, to red. Red light has the least energy of these light bands; blue is the
most energetic.
Beyond the red end of the
spectrum are the infrared (literally “beneath red”) lightwaves and radio
waves. We know that infrared light can be used as a form of heat. Radio waves
are harnessed to carry TV and radio transmissions.
Ultraviolet (literally
“beyond violet”) light, X-rays, and gamma-rays are beyond the blue/violet
end of the visible spectrum.
UV light (as well as X-rays
and gamma rays) is a form of radiation that is invisible to the human eye.
Radiated energy is given off by many objects, such as light bulbs, fire, and
stars. X-rays, gamma-rays, and UV light emitted by stars are absorbed by the
Earth’s atmosphere.
The UV Spectrum
UV light has shorter
wavelengths than visible light. It has four natural types of energy bands of its
own, though not all penetrate the upper atmosphere.
UVC
is shortwave UV; it includes germicidal UV. Like all lightwaves, it is measured
in nanometers (nm). UVC’s 220- to 290-nm wavelength can be used for air,
surface, and water disinfection. Overexposure to UVC causes skin redness and eye
irritation, but does not cause skin cancer or cataracts.
UVB
(290 to 315 nm) is the part of sunlight that leads to sunburn and skin cancer.
Most of the solar UVB is absorbed by the stratospheric ozone layer; however,
exposure can be dangerous.
UVA
(315 to 400 nm) is longwave UV, also known as blacklight. (For those of us who
had blacklight posters, or whose brothers had blacklight posters, it’s another
trip down memory lane.) UVA is responsible for safe skin tanning and is used to
treat certain skin disorders.
UVV
is also called vacuum UV; its wavelength is 187 nm. 187 nm is a naturally
occurring wavelength but it doesn’t usually penetrate the upper atmosphere.
UVC and UVV
UVC destroys the DNA of
microbial contaminants, rendering them sterile. If microbes are irradiated with
a large enough dose of UVC, they can no longer reproduce and over time disappear
from the indoor environment.
UV rays are made
artificially in UV lights by basically passing an electric current through a gas
or vapor. These lamps resemble ordinary fluorescent tubes. Sometimes these lamps
use a reflector for the UV rays; other models provide direct air and surface
sterilization by irradiating the air and surfaces in direct view of the lamp.
Some models provide indirect
air irradiation by enclosed UV lamps; these irradiate air as it passes through
the UV unit. These units are not used for surface irradiation. HVAC airstream
irradiation uses powerful, high-output UV lamps designed specifically for the
cold, moving air in ductwork. In-room, stationary UV may be used for surface and
indirect air irradiation in hospital operating rooms and laboratories. Extreme
care must be used in placing these so as not to shine them directly at
occupants.
“UVC’s primary uses are
for the destruction of bacteria and other microorganisms that pass through the
aluminum chamber.”. “The Centers for Disease Control recommends this method
for destroying viruses such as tuberculosis.
“UVV is primarily used for
oxidization; this is the portion of the lamp which will neutralize odors in the
air. Both UV wavelengths work together to destroy the contaminant,” the
company said. “UVC penetrates the cell’s membrane, destroying the cell’s
DNA. UVV destroys the chemicals of the dead cell.”
More Cool Stuff
When properly designed and
applied, HVAC coil irradiation units are said to produce a 99-percent kill rate
(according to a McGill University study using UV object cleaners). The most
effective practice is to combine coil irradiation with airstream irradiation.
However, is this necessary for all cases?
As you might expect, the
efficiency of UV Germicidal Irradiation (UVGI) decreases farther away from the
UV lamp. “A common misconception is that a UV lamp installed in a duct will
treat all the air passing by it. In fact, at just 2 inches from the surface of
the glass of the lamp, the UV efficiency drops more than 80 percent, and the
decline is exponential.
“This is true for all types of glass and lamps; this is a fundamental principle of UVC light.”
Call: Richard Fix 1-888-218-1146
Email: info@TheEscapeSystem.com