Infrared light (energy or heat, as it is commonly stated when referring
to infrared saunas) is part of the invisible light spectrum. Unlike
visible light, our bodies perceive this type of light as heat. Most
everything in the natural world produces infrared energy. Even things
that we think of as being very cold, like ice, radiate some infrared
energy. This energy can be felt when you hold your hand close to
your skin or by the warmth you feel from the sun when you
walk outside on cold but sunny day. Infrared light heats
up objects directly through a process called conversion, meaning
it can heat an object without having to heat the air in between.
WHAT MAKES THE HEAT?
Anything and everything produces infrared. The task of an infrared
heater is to produce infrared in a range that is beneficial to the
human body. The first thing to know is that there are a number of
different types of infrared heaters (ceramic, carbon/fiberglass, incoloy, mica and
aluminum). All infrared heaters are going to have some part of them
that is made of metal. This is absolutely necessary in order to
transfer the electricity from the power wires, and then to whatever
material is being used to produce the infrared heat.
IS ALL INFRARED THE SAME?
The short answer is no, it is not all the same. Remember that infrared
heat is a type of light, and one of the characteristics of light
is that it has a wavelength. One thing that varies among different
infrared saunas (and specifically their heaters) is the wavelength
of the infrared, which is usually expressed in a unit called microns.
To understand this more fully it's important to know that
the type and amount of infrared that is given off by an
infrared heater is based primarily on two things:
1.
The surface temperature of the source
2. The "emissivity" of the source
WHY IS TEMPERATURE IMPORTANT?
The temperature of a surface (the surface of the heater, for
example) plays the primary role in determining the wavelength
of the infrared.
The wavelength of the infrared in fact has a direct mathematical
relationship to the temperature, which is expressed in the formula
below:
Wien's Law: Wavelength = .2898 / (.56*(°F-32)+273)
- (modified for Fahrenheit, not Kelvin)
Using this formula, we can take a given temperature (in degrees
Fahrenheit) and determine a close approximation of the wavelength
of the infrared that is being emitted from the surface. Here are
two examples of heaters with surface temperature at 100° F and
300° F:
Temperature of 100 °F: .2898 / ( .56 * (100°F-32)
+ 273) = 9.32 microns
Temperature of 300 °F: .2898 / ( .56 * (300°F-32)
+ 273) = 6.85 microns
As you can see, the lower the surface temperature of the heater,
the longer the wave length. The reason this is important to understand
is that a lot of different infrared sauna companies try to differentiate
their products by talking about the "micron range" of
their heaters. Using this formula you can figure it out on your
own, if you choose to. You can even take it one step further by
asking, what is it that determines the temperature of the heaters?
The answer can often seem complicated, but ultimately it is a combination
of three factors: the surface area of the heater, the wattage of
the individual heater, and emissivity. The first two we'll cover
in our next section, all about infrared heaters, but first: on
to
emissivity.
WHAT IS EMISSIVITY?
In the simplest of terms, it is a measure of how much infrared
an object gives off, relative to how much energy is added to it
in the first place. Usually this is written as a fraction or percentage,
and is technically measured by comparing the actual surface to a
hypothetically "perfect" surface (called a black body).
So, when you're looking at the actual number, you can think of it
like a percentage that tells you how efficient a particular type
of surface is. For example, (remember: this is in simplified terms)
an emissivity of .91 can be thought of as being 91%. The breakdown
then, is that the higher the emissivity, the more efficient
that surface is at producing infrared from a given amount of energy.
For a really good technical definition of emissivity, you can go
here. Also, for the emissivity of specific materials, you can go
here. It's important to remember that Wien's equation above assumes
the use of a perfect black body, which is why it is only a close
approximation. However, the closer a surface's emissivity gets to
being 1.00, the more useful and accurate that surface is going to
be. For example, Wien's law would be more accurate in calculating
infrared for a surface with high emissivity (such as ceramic), than
for a surface with lower emissivity (such as aluminum or carbon).
PEAK WAVELENGTH
Using some of the methods described above, some infrared sauna
companies will measure the "peak wavelength" of their
infrared heaters. A peak wavelength is the highest occurrence of
any single wavelength produced by their infrared heaters. Though
it is certainly possible to measure this peak wavelength, the practice
is one that can be deceptive to potential buyers. Since many buyers
are seeking longer wavelength infrared, infrared sauna companies
sometimes seek to exaggerate the typical wavelength produced by
their infrared saunas.
Specifically, for anyone to claim that the “peak wavelength”
of their infrared sauna heaters are 9.7 or 9.4 microns, the average
surface temperature of those infrared sauna heaters would have to
be less than 100° F. Since this is very close to our natural
body temperature, you should be wary about the validity of this
claim. When you factor in that almost ALL infrared sauna heaters
run at several hundred degrees, it becomes hard to support claims
that peak wavelengths are really that high.
PLEASE NOTE: The information in this infrared
sauna guide is free to print and distribute as long as it is not
modified in any way. Any publishing of this information on the Internet
does require a link placed back to this site.
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