Spectral absorbance in frequency and spectral absorbance in wavelength of a material, denoted Aν and Aλ respectively, are given by[1]

A common expression of the Beer's law relates the attenuation of light in a material as: A = ε ℓ c {\displaystyle \mathrm {A} =\varepsilon \ell c} , where A {\displaystyle \mathrm {A} } is the absorbance; ε {\displaystyle \varepsilon } is the molar attenuation coefficient or absorptivity of the attenuating species; ℓ {\displaystyle \ell } is the optical path length; and c {\displaystyle c} is the concentration of the attenuating species.

When choosing a device, look for one with an irradiance zone between 20 and 200 mW/cm2 for the best results. Only devices with the right combination of energy density, irradiance, and wavelengths will be able to provide effective treatment.

When it comes to red light, some therapeutic wavelengths belong to the visible spectrum and some to those that are not visible to the human eye. In general, light from the visible spectrum usually has a more surface effect, whereas light from the invisible spectrum, such as near-infrared light, normally penetrates deeper into the tissue.

Near-infraredwavelength

Another group of researchers has been using various frequencies of red and near-infrared light to show that they can combine them together for bone and tooth regeneration. The examples of successful and exciting uses of combined frequencies are numerous.

If you have narrowed down your therapy of choice to red light therapy, there is still a world of options when it comes to different frequencies used for treatments. Here are some factors you should consider when deciding on the optimal red light wavelengths for your health.

Infrared wavelengthrange in m

If a(z) is uniform along the path, the attenuation is said to be a linear attenuation, and the relation becomes A = a l . {\displaystyle A=al.}

Some devices are in a form of face masks and their use is for purely cosmetic reasons. The most common and versatile type of device is red light therapy panels, which can range in size, features, and number of lamps.

Also, remember to hydrate and use the sauna in moderation, as excessive use can lead to dehydration or, in rare cases, even to thermal injuries.

Infraredfrequency

An Ultraviolet-visible spectroscopy#Ultraviolet–visible spectrophotometer will do all this automatically. To use this machine, solutions are placed in a small cuvette and inserted into the holder. The machine is controlled through a computer and, once it has been "blanked", automatically displays the absorbance plotted against wavelength. Getting the absorbance spectrum of a solution is useful for determining the concentration of that solution using the Beer–Lambert law and is used in HPLC.

For instance, one recent study has shown that red and near-infrared light together applied intranasally can be an effective treatment for allergies.

The roots of the term absorbance are in the Beer–Lambert law. As light moves through a medium, it will become dimmer as it is being "extinguished". Bouguer recognized that this extinction (now often called attenuation) was not linear with distance traveled through the medium, but related by what we now refer to as an exponential function.

Absorbance is a dimensionless quantity. Nevertheless, the absorbance unit or AU is commonly used in ultraviolet–visible spectroscopy and its high-performance liquid chromatography applications, often in derived units such as the milli-absorbance unit (mAU) or milli-absorbance unit-minutes (mAU×min), a unit of absorbance integrated over time.[6]

Most low-level laser therapy devices and LED red light therapy devices use visible red and near-infrared light. Visible red light has a wavelength between 600 and 650 nanometers. The wavelength of near-infrared light is between 650 and 1100 nanometers. Combining the two usually gives the best results.

When choosing your red light therapy device, the wavelengths of light are not the only factor you should be looking at. Here are some other important factors that are crucial in deciding which device is the best for you.

Φ e t + Φ e a t t = Φ e i + Φ e e , {\displaystyle \Phi _{\mathrm {e} }^{\mathrm {t} }+\Phi _{\mathrm {e} }^{\mathrm {att} }=\Phi _{\mathrm {e} }^{\mathrm {i} }+\Phi _{\mathrm {e} }^{\mathrm {e} }\,,}

Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)".[1] Alternatively, for samples which scatter light, absorbance may be defined as "the negative logarithm of one minus absorptance, as measured on a uniform sample".[2] The term is used in many technical areas to quantify the results of an experimental measurement. While the term has its origin in quantifying the absorption of light, it is often entangled with quantification of light which is "lost" to a detector system through other mechanisms. What these uses of the term tend to have in common is that they refer to a logarithm of the ratio of a quantity of light incident on a sample or material to that which is detected after the light has interacted with the sample.

Any real measuring instrument has a limited range over which it can accurately measure absorbance. An instrument must be calibrated and checked against known standards if the readings are to be trusted. Many instruments will become non-linear (fail to follow the Beer–Lambert law) starting at approximately 2 AU (~1% transmission). It is also difficult to accurately measure very small absorbance values (below 10−4) with commercially available instruments for chemical analysis. In such cases, laser-based absorption techniques can be used, since they have demonstrated detection limits that supersede those obtained by conventional non-laser-based instruments by many orders of magnitude (detection has been demonstrated all the way down to 5×10−13). The theoretical best accuracy for most commercially available non-laser-based instruments is attained in the range near 1 AU. The path length or concentration should then, when possible, be adjusted to achieve readings near this range.

Ultraviolet light, which is harmful to the human skin, has the shortest wavelength, whereas red light has the longest wavelength.

A ν = log 10 ⁡ Φ e , ν i Φ e , ν t = − log 10 ⁡ T ν , A λ = log 10 ⁡ Φ e , λ i Φ e , λ t = − log 10 ⁡ T λ , {\displaystyle {\begin{aligned}A_{\nu }&=\log _{10}{\frac {\Phi _{{\text{e}},\nu }^{\text{i}}}{\Phi _{{\text{e}},\nu }^{\text{t}}}}=-\log _{10}T_{\nu }\,,\\A_{\lambda }&=\log _{10}{\frac {\Phi _{{\text{e}},\lambda }^{\text{i}}}{\Phi _{{\text{e}},\lambda }^{\text{t}}}}=-\log _{10}T_{\lambda }\,,\end{aligned}}}

Beyond the range of visible red light is the range of infrared light. This is light that ranges from 700 nm to 1 mm. Depending on the wavelength, infrared light can be on the spectrum of the near infrared, mid-infrared, and far infrared. The longer the wavelength, the deeper into the body the light penetrates. However, longer wavelengths also emit more heat.

Infrared wavelengthrange in nm

where μ {\displaystyle \mu } is called an attenuation constant (a term used in various fields where a signal is transmitted though a medium) or coefficient. The amount of light transmitted is falling off exponentially with distance. Taking the natural logarithm in the above equation, we get

A = log 10 ⁡ Φ e i Φ e t = − log 10 ⁡ T , {\displaystyle A=\log _{10}{\frac {\Phi _{\text{e}}^{\text{i}}}{\Phi _{\text{e}}^{\text{t}}}}=-\log _{10}T,}

Longer wavelengths is what far infrared saunas use. That is because infrared light doesn’t actually use its light energy to heal the body, but instead uses heat. Unlike regular saunas which use steam or hot stones as their heat source, an infrared sauna uses lamps that emit far infrared light.

Absorbance is a number that measures the attenuation of the transmitted radiant power in a material. Attenuation can be caused by the physical process of "absorption", but also reflection, scattering, and other physical processes. Absorbance of a material is approximately equal to its attenuance[clarification needed] when both the absorbance is much less than 1 and the emittance of that material (not to be confused with radiant exitance or emissivity) is much less than the absorbance. Indeed,

Infrareduses

For example, if the filter has 0.1% transmittance (0.001 transmittance, which is 3 absorbance units), its shade number would be 8.

S N = 7 3 A + 1 = 7 3 ( − log 10 ⁡ T ) + 1 . {\displaystyle {\begin{aligned}\mathrm {SN} &={\frac {7}{3}}A+1\\&={\frac {7}{3}}(-\log _{10}T)+1\,.\end{aligned}}}

If a size of a detector is very small compared to the distance traveled by the light, any light that is scattered by a particle, either in the forward or backward direction, will not strike the detector. (Bouguer was studying astronomical phenomena, so this condition was met.) In such case, a plot of − ln ⁡ ( T ) {\displaystyle -\ln(T)} as a function of wavelength will yield a superposition of the effects of absorption and scatter. Because the absorption portion is more distinct and tends to ride on a background of the scatter portion, it is often used to identify and quantify the absorbing species. Consequently, this is often referred to as absorption spectroscopy, and the plotted quantity is called "absorbance", symbolized as A {\displaystyle \mathrm {A} } . Some disciplines by convention use decadic (base 10) absorbance rather than Napierian (natural) absorbance, resulting in: A 10 = μ 10 d {\displaystyle \mathrm {A} _{10}=\mu _{10}d} (with the subscript 10 usually not shown).

A ν = τ ν ln ⁡ 10 = τ ν log 10 ⁡ e , A λ = τ λ ln ⁡ 10 = τ λ log 10 ⁡ e , {\displaystyle {\begin{aligned}A_{\nu }&={\frac {\tau _{\nu }}{\ln 10}}=\tau _{\nu }\log _{10}e\,,\\A_{\lambda }&={\frac {\tau _{\lambda }}{\ln 10}}=\tau _{\lambda }\log _{10}e\,,\end{aligned}}}

The energy density is almost as important as the wavelength of light. Optimal energy density allows for the best results even when the device is used for relatively short treatments. Energy density is expressed in J/cm2 and should be no higher than 100 J/cm2. The exact energy density used for a particular treatment depends on the type and duration of the treatment.

− ln ⁡ ( T ) = ln ⁡ I 0 I s = ( μ s + μ a ) d . {\displaystyle -\ln(T)=\ln {\frac {I_{0}}{I_{s}}}=(\mu _{s}+\mu _{a})d\,.}

Infrared light wavelengthand frequency

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Nowadays, red light therapy devices come in all shapes and sizes. Doctors’ offices usually have stronger devices that are not that common in other places and require medical professionals to handle them. Home-use devices are optimized for daily use.

When it comes to treatments, there is not just one magic wavelength with therapeutic properties. For instance, even UV light has the potential for the treatment of some conditions like seasonal depression.  However, people usually avoid it because of the associated health risks.

The term absorption refers to the physical process of absorbing light, while absorbance does not always measure only absorption; it may measure attenuation (of transmitted radiant power) caused by absorption, as well as reflection, scattering, and other physical processes. Sometimes the term "attenuance" or "experimental absorbance" is used to emphasize that radiation is lost from the beam by processes other than absorption, with the term "internal absorbance" used to emphasize that the necessary corrections have been made to eliminate the effects of phenomena other than absorption.[3]

Modern red light therapy devices for home use are optimized to offer the most effective wavelengths. For example, FlexBeam uses a combination of red light at 610-650nm and near-infrared light at 800-850nm.

Infraredenergy

Even though this absorbance function is very useful with scattering samples, the function does not have the same desirable characteristics as it does for non-scattering samples. There is, however, a property called absorbing power which may be estimated for these samples. The absorbing power of a single unit thickness of material making up a scattering sample is the same as the absorbance of the same thickness of the material in the absence of scatter.[5]

Photobiomodulation or light therapy consists of a rich array of treatments that all work through different mechanisms to solve various health problems. If you want to boost your overall health or support your body in its healing efforts you should be looking into red light wavelengths and how they can help. You might be wondering how exactly to choose the right type of light therapy for you.

For samples which scatter light, absorbance is defined as "the negative logarithm of one minus absorptance (absorption fraction: α {\displaystyle \alpha } ) as measured on a uniform sample".[2] For decadic absorbance,[3] this may be symbolized as A 10 = − log 10 ⁡ ( 1 − α ) {\displaystyle \mathrm {A} _{10}=-\log _{10}(1-\alpha )} . If a sample both transmits and remits light, and is not luminescent, the fraction of light absorbed ( α {\displaystyle \alpha } ), remitted ( R {\displaystyle R} ), and transmitted ( T {\displaystyle T} ) add to 1: α + R + T = 1 {\displaystyle \alpha +R+T=1} . Note that 1 − α = R + T {\displaystyle 1-\alpha =R+T} , and the formula may be written as A 10 = − log 10 ⁡ ( R + T ) {\displaystyle \mathrm {A} _{10}=-\log _{10}(R+T)} . For a sample which does not scatter, R = 0 {\displaystyle R=0} , and 1 − α = T {\displaystyle 1-\alpha =T} , yielding the formula for absorbance of a material discussed below.

For scattering media, the constant is often divided into two parts,[4] μ = μ s + μ a {\displaystyle \mu =\mu _{s}+\mu _{a}} , separating it into a scattering coefficient μ s {\displaystyle \mu _{s}} and an absorption coefficient μ a {\displaystyle \mu _{a}} , obtaining

In optics, absorbance or decadic absorbance is the common logarithm of the ratio of incident to transmitted radiant power through a material, and spectral absorbance or spectral decadic absorbance is the common logarithm of the ratio of incident to transmitted spectral radiant power through a material. Absorbance is dimensionless, and in particular is not a length, though it is a monotonically increasing function of path length, and approaches zero as the path length approaches zero.

Within a homogeneous medium such as a solution, there is no scattering. For this case, researched extensively by August Beer, the concentration of the absorbing species follows the same linear contribution to absorbance as the path-length. Additionally, the contributions of individual absorbing species are additive. This is a very favorable situation, and made absorbance an absorption metric far preferable to absorption fraction (absorptance). This is the case for which the term "absorbance" was first used.

It is essential to do your research when you are buying your red light therapy device for home use and find the one with optimal performance and features for your particular health concerns. However, don’t focus too much on the details.

Although absorbance is properly unitless, it is sometimes reported in "absorbance units", or AU. Many people, including scientific researchers, wrongly state the results from absorbance measurement experiments in terms of these made-up units.[7]

The amount of light transmitted through a material diminishes exponentially as it travels through the material, according to the Beer–Lambert law (A = (ε)(l)). Since the absorbance of a sample is measured as a logarithm, it is directly proportional to the thickness of the sample and to the concentration of the absorbing material in the sample. Some other measures related to absorption, such as transmittance, are measured as a simple ratio so they vary exponentially with the thickness and concentration of the material.

Infraredradiation examples

Light is a wave and, simply put, light wavelength is the distance between two peaks in the wave. The bigger the distance – the longer the wavelength. Wavelength determines certain properties of the light, for instance, whether it belongs to the visible spectrum or what color it is.

If I 0 {\displaystyle I_{0}} is the intensity of the light at the beginning of the travel and I d {\displaystyle I_{d}} is the intensity of the light detected after travel of a distance d {\displaystyle d} , the fraction transmitted, T {\displaystyle T} , is given by

Typically, absorbance of a dissolved substance is measured using absorption spectroscopy. This involves shining a light through a solution and recording how much light and what wavelengths were transmitted onto a detector. Using this information, the wavelengths that were absorbed can be determined.[8] First, measurements on a "blank" are taken using just the solvent for reference purposes. This is so that the absorbance of the solvent is known, and then any change in absorbance when measuring the whole solution is made by just the solute of interest. Then measurements of the solution are taken. The transmitted spectral radiant flux that makes it through the solution sample is measured and compared to the incident spectral radiant flux. As stated above, the spectral absorbance at a given wavelength is

At the end of the day, the most important thing is the convenience of use. Consistent use will yield the best results, regardless of the finer details.

Whereas there are benefits to saunas that use far infrared light, there are also certain risks that you should bear in mind. Before using an infrared sauna, you should consult your doctor, especially if you have pre-existing medical conditions.

A λ = log 10 ( Φ e , λ i Φ e , λ t ) . {\displaystyle A_{\lambda }=\log _{10}\!\left({\frac {\Phi _{\mathrm {e} ,\lambda }^{\mathrm {i} }}{\Phi _{\mathrm {e} ,\lambda }^{\mathrm {t} }}}\right)\!.}

*FlexBeam is not intended to diagnose, cure, or prevent specific diseases or medical conditions. The recharge.health website is for education and information purposes only and not intended as medical advice. For treating any serious medical condition, professional medical attention should be sought.

Some devices, like FlexBeam, are portable, and can be wrapped around or pressed against the affected body part for targeted treatments. This ensures better and faster results.

The color of the light is determined by its wavelength, and research shows that lights of different colors produce different results. For example, one study showed that red and green light promoted the proliferation of human umbilical vein cells, whereas blue light inhibited metabolic activity in the cells.

Sometimes the relation is given using the molar attenuation coefficient of the material, that is its attenuation coefficient divided by its molar concentration: