Figure 8 illustrates what happens when unpolarized light is reflected from a surface. Vertically polarized light is preferentially refracted at the surface, so that the reflected light is left more horizontally polarized. The reasons for this phenomenon are beyond the scope of this text, but a convenient mnemonic for remembering this is to imagine the polarization direction to be like an arrow. Vertical polarization would be like an arrow perpendicular to the surface and would be more likely to stick and not be reflected. Horizontal polarization is like an arrow bouncing on its side and would be more likely to be reflected. Sunglasses with vertical axes would then block more reflected light than unpolarized light from other sources.

(A) Planck’s law. Dependence of spectral radiant emittance (ωλ) for perfect blackbodies as a function of wavelength (λ). (B) Wien’s displacement law. The wavelength of maximal radiant exitance (λmax) as a function of the absolute temperature (T) for a perfect black body (dashed line) and different bodies.

When the intensity is reduced by 90.0% it is 10% or 0.100 times its original value. That is, I = 0.100 I0. Using this information, the equation I = I0 cos2θ can be used to solve for the needed angle.

To examine this further, consider the transverse waves in the ropes shown in Figure 3. The oscillations in one rope are in a vertical plane and are said to be vertically polarized. Those in the other rope are in a horizontal plane and are horizontally polarized. If a vertical slit is placed on the first rope, the waves pass through. However, a vertical slit blocks the horizontally polarized waves. For EM waves, the direction of the electric field is analogous to the disturbances on the ropes.

Polarisationmeaning in Physics

Medical FIR sources. (A) WS TY-301R® and (B, C) WS TY-101N® FIR lamps (both by WS Far Infrared Medical Technology Co., Ltd., Taipei, Taiwan).

In the IR radiation bands, only FIR transfers energy purely in the form of heat which can be perceived by the thermoreceptors in human skin as radiant heat [1]. Not only is FIR absorbed by the human body but it is also emitted by the body in the form of black body radiation (3–50 μm with an output peak at 9.4 μm).

The term “black body” was first used by Gustav Kirchoff in 1860. In essence, all matter absorbs electromagnetic radiation to some degree and an object that absorbs all radiation falling on it (at all wavelengths and frequencies) is called a black body, i.e., a perfect absorber. When a black body is at a uniform temperature state, it emits back this absorbed energy, and it is termed as “ black body radiation ”. This is a type of radiation and has continuous frequency/intensity which depends only on the black body’s temperature, and the type of spectrum it generates is called the Planck spectrum. In this type of spectrum, spectral peaks at characteristic frequencies are shifted to higher values (shorter wavelengths) with increasing temperature values. For instance, at room temperature most of the emission of the black body is in the infrared region of the electromagnetic spectrum. At a typical environmental background temperature, which is around 300 K, the peak emission is at about 9.7 μm (and the curve covers the FIR region as well); at around 1800 K (temperature of molten steel), the peak is shifted to 1.6 μm; at around 6000 K (surface temperature of the sun), the peak is shifting even further, 0.48 μm, which now is in the visible (blue) region of the spectrum. Peak shifts of some representative black body temperatures and the range of electromagnetic radiation they fall into are given in Figure 2A, B. This type of shift in the emission peaks of the black bodies (to shorter wavelengths at higher temperatures) is governed by Wien’s displacement law.

Examples of polarization in society

5: When particles scattering light are much smaller than its wavelength, the amount of scattering is proportional to 1/ λ4. Does this mean there is more scattering for small λ than large λ? How does this relate to the fact that the sky is blue?  Hint:  red light has a wavelength of about 650 nm while blue light has a wavelength of about 400 nm.

Linear polarization

In living systems, in addition to the water molecules association with the electromagnetic field and effects of that, one has to consider the “meso-structure” effect where proteins and charged groups (located at specific sites on the proteins) are crucial for the overall biological activity. These specifically located charged groups associate with the water molecules and by doing this influence the dielectric behavior of the whole molecular-assembly, which in turn effects its biologic functioning. Thus, the dielectric properties of tissues (even at cellular level) depend on and vary with the water content. In addition, the relaxation of these molecular “meso-structures” can show variations with frequency. For these reasons, water content is a critical factor in the interaction between FIR and living organisms.

(a) On a day when the intensity of sunlight is 1.00 kW/m2, a circular lens 0.200 m in diameter focuses light onto water in a black beaker. Two polarizing sheets of plastic are placed in front of the lens with their axes at an angle of 20.0o. Assuming the sunlight is unpolarized and the polarizers are 100% efficient, what is the initial rate of heating of the water in oC/s, assuming it is 80.0% absorbed? The aluminum beaker has a mass of 30.0 grams and contains 250 grams of water. (b) Do the polarizing filters get hot? Explain.

By now you can probably guess that Polaroid sunglasses cut the glare in reflected light because that light is polarized. You can check this for yourself by holding Polaroid sunglasses in front of you and rotating them while looking at light reflected from water or glass. As you rotate the sunglasses, you will notice the light gets bright and dim, but not completely black. This implies the reflected light is partially polarized and cannot be completely blocked by a polarizing filter.

There have been a few laboratory studies that have reported the biological effects of FIR. A recent important paper describes the in vitro use of an FIR generator (WS TY-301R®; M/s WS Far Infrared Medical Technology Co., Ltd., Taipei, Taiwan; see Figure 3) as a radiation source to irradiate human umbilical vein endothelial cells (HUVECs) [4]. In the study, FIR exposure (a low non-thermal irradiance) of 0.13 mW/cm2 for 30 min inhibited proliferation and the vascular endothelial growth factor (VEGF)-induced phosphorylation of extracellular signal-regulated kinases in HUVECs. Furthermore, FIR exposure induced the phosphorylation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) generation in VEGF-treated HUVECs. Both VEGF-induced NO and reactive oxygen species (ROS) generation was involved in the inhibitory effect of FIR. Nitrotyrosine formation increased significantly in HUVECs treated with VEGF and FIR together. Inhibition of phosphoinositide 3-kinase (PI3K) by wortmannin abolished both the FIR-induced phosphorylation of eNOS and serine/threonine-specific protein kinase in HUVECs. In addition to that, FIR exposure upregulated the expression of PI3K p85 at the transcriptional level. It was observed that FIR exposure induced the nuclear translocation of promyelocytic leukemia zinc finger protein in the cells. These data provide information on how FIR exposure could affect microcirculation, independent from thermal effects. The same group had previously shown that non-thermal FIR therapy increased skin blood flow in rats [5]. Toyokawa et al. [6] used home-made ceramic FIR emitters to stimulate full thickness excisional skin wound healing in rats. After constant exposure to FIR, wound healing was significantly quickened and transforming growth factor (TGF)-beta1 expressing myofibroblasts and collagen content were increased.

where Io is the intensity of the polarized wave before passing through the filter. (The above equation is known as Malus’s law.)

If you hold your Polaroid sunglasses in front of you and rotate them while looking at blue sky, you will see the sky get bright and dim. This is a clear indication that light scattered by air is partially polarized. Figure 11 helps illustrate how this happens. Since light is a transverse EM wave, it vibrates the electrons of air molecules perpendicular to the direction it is traveling. The electrons then radiate like small antennae. Since they are oscillating perpendicular to the direction of the light ray, they produce EM radiation that is polarized perpendicular to the direction of the ray. When viewing the light along a line perpendicular to the original ray, as in Figure 11, there can be no polarization in the scattered light parallel to the original ray, because that would require the original ray to be a longitudinal wave. Along other directions, a component of the other polarization can be projected along the line of sight, and the scattered light will only be partially polarized. Furthermore, multiple scattering can bring light to your eyes from other directions and can contain different polarizations.

In this regard, the dynamics of water-clusters has attracted considerable interest since there is a noticeable difference with respect to the dynamics of bulk-liquid-water, and this may have significant implications in biological environments. Local changes in the molecular environment (caused by solvation or confinement) are shown to affect substantially the translational and vibrational modes in FIR frequency range. It is found that water cluster size and temperature affect the FIR absorption spectrum significantly [3].

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In these cabins, the heating elements are typically heated to about 300– 400° C and the emission is in the FIR range, that is, the heat exchange between the body and the environment is almost purely radiative (radiant heating) with cabin air temperature being at around 40°C or less (Figure 4). Heating of the skin with FIR warming cabins is faster (in comparison with the conventional saunas) but higher irradiance of the skin must be applied in order to produce noticeable sweating. These cabins are frequently used in Japan where the practice is called “Waon therapy” [20, 21]. Waon therapy has been used extensively in Japan [22] and Korea [23] for cardiovascular conditions and diseases, particularly chronic heart failure [24, 25] and peripheral arterial disease [26, 27]. FIR sauna therapy has been used to improve cardiac and vascular function and reduce oxidative stress in patients with chronic heart failure [28]. Beever [29] asked whether FIR saunas could have a beneficial effect on quality of life in those patients with type II diabetes. The study consisted of 20 min, three times weekly infrared sauna sessions, over a period of 3 months. Physical health, general health, social functioning indices, and visual analogue scales (VAS) measurements for stress and fatigue all improved in the treatment group. A study of patients with rheumatoid arthritis and ankylosing spondylitis showed a reduction in pain, stiffness, and fatigue during infrared sauna therapy [30].

In flat screen LCD televisions, there is a large light at the back of the TV. The light travels to the front screen through millions of tiny units called pixels (picture elements). One of these is shown in Figure 12 (a) and (b). Each unit has three cells, with red, blue, or green filters, each controlled independently. When the voltage across a liquid crystal is switched off, the liquid crystal passes the light through the particular filter. One can vary the picture contrast by varying the strength of the voltage applied to the liquid crystal.

For FIR used as a therapeutic modality the alternative terms “biogenetic radiation” and “biogenetic rays” have been coined and widely used in the popular literature. FIR wavelength is too long to be perceived by the eyes, however, the body experiences its energy as a gentle radiant heat which can penetrate up to 1.5 inches (almost 4 cm) beneath the skin. FIR energy is sufficient to exert rotational and vibrational modes of motion in bonds forming the molecules (including the water molecules) as well as resonate with cellular frequencies. Resulting epidermal temperature is higher when the skin is irradiated with FIR than if similar thermal loads from shorter wavelengths are used. The prolonged erythermal response due to FIR exposure has been proposed to be due to increased epidermal temperatures associated with it, but levels of FIR that do not produce any detectable skin heating can also have biological effects.

4: Explain what happens to the energy carried by light that it is dimmed by passing it through two crossed polarizing filters.

1: What angle is needed between the direction of polarized light and the axis of a polarizing filter to cut its intensity in half?

Since the part of the light that is not reflected is refracted, the amount of polarization depends on the indices of refraction of the media involved. It can be shown that reflected light is completely polarized at a angle of reflection θb, given by

With respect to the complete electromagnetic radiation spectrum, the infrared radiation (IR) band covers the wavelength range of 750 nm–100 μm, frequency range of 400 THz–3 THz, and photon energy range of 12.4 meV– 1.7 eV. It lies between the long wavelength red edge of the visible and the short edge of the terahertz (starting at 3 THz) spectral bands (Figure 1).

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It must be emphasized that the above remains a hypothetical explanation at present, but is clearly a testable hypothesis. One could ask whether exposure of cells to non-heating FIR can affect mitochondria by for instance increasing ATP, increasing oxygen consumption, producing NO and ROS, affecting MMP and calcium levels. One could also ask whether cells that are rich in mitochondria respond well to non-heating FIR, in the same way as they do to LLLT.

It cannot be excluded that FIR could itself have effects on CCO activity. A recent study has elucidated the existence of weakly H-bonded water molecules in bovine CCO that might change during catalysis [55]. Fitting with Gaussian components indicated the involvement of up to eight waters in the photolysis transition. The fact that Fourier transform infrared (FTIR) spectroscopy is extensively employed to study the structure, function, and dynamics of CCO [56, 57] suggests that it is possible that the same wavelengths (FIR uses comparable wavelengths to FTIR) could produce changes in conformation affecting enzyme activity or binding of NO to the CuB site.

While you are undoubtedly aware of liquid crystal displays (LCDs) found in watches, calculators, computer screens, cellphones, flat screen televisions, and other myriad places, you may not be aware that they are based on polarization. Liquid crystals are so named because their molecules can be aligned even though they are in a liquid. Liquid crystals have the property that they can rotate the polarization of light passing through them by 90o. Furthermore, this property can be turned off by the application of a voltage, as illustrated in Figure 12. It is possible to manipulate this characteristic quickly and in small well-defined regions to create the contrast patterns we see in so many LCD devices.

14: If θb is Brewster’s angle for light reflected from the top of an interface between two substances, and θb‘  is Brewster’s angle for light reflected from below, prove that θb + θb‘ = 90o..

5: At the end of Example 1, it was stated that the intensity of polarized light is reduced to 90.0% of its original value by passing through a polarizing filter with its axis at an angle of 18.4 degrees to the direction of polarization. Verify this statement.

In their most recent study the Leung group studied the repair effect of cFIR in human breast epithelial cells (MCF-10A) after H2O2 and after ionizing radiation from an X-ray source [19]. Their results show that in both, H2O2 toxicity and radiation exposure models, the cFIR treated cells demonstrated significantly higher cell survival rates than the control groups. In view of the experimental results and taking into account the relationship between indirect ionizing radiation and the oxidative stress-induced cell damage, and accumulation of free radicals, they proposed that the ionizing radiation protective ability of cFIR occurs predominantly through an antioxidant mechanism. They are suggesting that cFIR provides cells with a defensive mechanism during the irradiation process and promotes cell repair during post exposure period through hydrogen peroxide scavenging and COX-2 inhibiting activities.

Many crystals and solutions rotate the plane of polarization of light passing through them. Such substances are said to be optically active. Examples include sugar water, insulin, and collagen (see Figure 13). In addition to depending on the type of substance, the amount and direction of rotation depends on a number of factors. Among these is the concentration of the substance, the distance the light travels through it, and the wavelength of light. Optical activity is due to the asymmetric shape of molecules in the substance, such as being helical. Measurements of the rotation of polarized light passing through substances can thus be used to measure concentrations, a standard technique for sugars. It can also give information on the shapes of molecules, such as proteins, and factors that affect their shapes, such as temperature and pH.

7: When light is reflected at Brewster’s angle from a smooth surface, it is 100% polarized parallel to the surface. Part of the light will be refracted into the surface. Describe how you would do an experiment to determine the polarization of the refracted light. What direction would you expect the polarization to have and would you expect it to be 100 %?

What is polarization in Chemistry

Find Polaroid sunglasses and rotate one while holding the other still and look at different surfaces and objects. Explain your observations. What is the difference in angle from when you see a maximum intensity to when you see a minimum intensity? Find a reflective glass surface and do the same. At what angle does the glass need to be oriented to give minimum glare?

where n1 is the medium in which the incident and reflected light travel and n2 is the index of refraction of the medium that forms the interface that reflects the light. This equation is known as Brewster’s law, and θb is known as Brewster’s angle, named after the 19th-century Scottish physicist who discovered them.

What angle is needed between the direction of polarized light and the axis of a polarizing filter to reduce its intensity by 90.0 %?

2: The angle between the axes of two polarizing filters is 45.0 degrees. By how much does the second filter reduce the intensity of the light coming through the first?

Ishibashi et al. [8] did an in vitro study with five human cancer cell lines (A431, vulva; HSC3, tongue; Sa3, gingival; A549, lung; and MCF7, breast) to assess the effects of FIR irradiation. For that purpose, they used a tissue culture incubator with an imbedded FIR lamp that could continuously irradiate cells with FIR (lamp operating wavelength range being 4–20 μm with an emission peak height at 7 –12 μm). The overall observation was that the FIR effect varied in these five cancer cell line types, as can be expected. The study results showed that basal expression level of heat shock protein (HSP) 70A mRNA was higher in A431 and MCF7 cell lines in comparison with the FIR-sensitive HSC3, Sa3, and A549 cell lines. The study showed that the over expression of HSP70 inhibited FIR-induced growth arrest in HSC3 cells, and that HSP70 siRNA inhibited the proliferation of A431 cells after FIR treatment. A summary of the results of this study indicated that the proliferation-suppressing effect of FIR, in some cancer cell lines, is controlled by the basal expression level of the HSP70A. These findings suggest that FIR irradiation may be used as an effective medical treatment avenue for some cancer cells which have low levels of HSP70.

Polarization by reflection

Since the principle chromophore at FIR wavelengths is not CCO but rather water, we must ask ourselves how can the biological effects of red and NIR absorption be so similar to those seen with FIR ? Perhaps some clue can be obtained by considering the difference between the two types of FIR therapy (heating and non-heating). While heating FIR therapy is reported to increase blood flow, this result may be the simple response of increased thermoregulation that is known to occur when tissue is warmed. However, it is possible that the increase in blood flow, seen in non-heating FIR therapy, may be similar in nature to that seen in LLLT, in other words, a vasodilation due to NO release from stores in CCO [48] as well as from NO bound to hemoglobin and myoglobin [49]. How are we to explain cellular responses from low fluences of FIR that are insufficient to produce bulk heating of water in the tissue ? Perhaps the answer lies in the concept of nanostructured water layers [50]. These are thin (nano meters) layers of water that build up on hydrophobic surfaces such as cellular membranes, and they can be considered as “concentrated water ” [51]. If this description is correct, it is reasonable to assume that relatively small amounts of vibrational energy delivered by non-heating FIR could perturb the structure of the membrane underlying the nanoscopic water layer without bulk heating. Small perturbations in membrane structure could have big effects at the cell level if the membrane contains an ion channel. Ion channels (many kinds for both cations and anions [52]) are present in all cell membranes, but are particularly common in mitochondrial membranes (both inner and outer [53]). If mitochondrial ion channels (particularly calcium channels [54]) could be opened by non-heating FIR, thus increasing mitochondrial respiration, it would explain how the overall therapeutic outcomes of LLLT and non-heating FIR therapy are so similar.

If a polarizing filter reduces the intensity of polarized light to 50.0 %  of its original value, by how much are the electric and magnetic fields reduced?

Belts made out of these fabrics have been used for weight reduction. In one study, Conrado and Munin [37] investigated whether the use of a garment made with synthetic fibers embedded with powdered ceramic led to a reduction in body measurements. The study population comprised 42 women divided into two groups: active and placebo. The volunteers used clothing either impregnated or not impregnated with ceramic powder for at least 8 h/day for 30 days. The experimental data showed a reduction in body measurements, which may be a consequence of an increment in microcirculation and peripheral blood flow, and these changes might promote improved general health.

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FIR application in medicine requires understanding and knowledge of the interactions of electromagnetic radiation at FIR range with biological structures (including cells, cell membranes, cell fluids – especially water, DNA/proteins) and functioning of the living systems in general. At the cellular level, the underlying biophysical mechanisms of the interaction of electromagnetic radiation with living cells can be framed in terms of altered cell membrane potentials and altered mitochondrial metabolism [2]. FIR energy (photons with quantum energy levels of 12.4 meV –1.7 eV) is absorbed by vibrational levels of bonds in molecules. There are six vibrational modes covering symmetric and antisymmetric stretching, scissoring, rocking, wagging and twisting. Considering the high concentration of water in biological systems, association of water molecules with ions (solvation effect), the dielectric properties of the water and the large dipole moment that this effect generates, this will be a dominant factor in biological solutions. It is known that at lower frequencies water molecules are able to rotate freely in an oscillating electric field with little or almost no energy loss. However, if the frequency of the electric field reaches 108 Hz levels, the rotational mode becomes hindered (due to “dielectric friction ” effect) and the absorbed energy starts dissipating by collision or nearest neighbor interactions in the media [2]. The dielectric relaxation of water at 310 K is around 25 GHz where the rotational response of the dipoles to the electromagnetic field is spread over a broad frequency range.

Along the same lines, Akasaki et al. [7] studied in vivo the effects of repeated FIR irradiation on angiogenesis in a mouse model of hindlimb ischemia. Following reports that FIR therapy upregulated the expression of arterial eNOS in hamsters (and it is known that NO constitutively produced by eNOS plays an important role in angiogenesis) they took a step further to investigate whether the FIR therapy increases angiogenesis in mice with the hindlimb ischemia. In their study, unilateral hindlimb ischemia was induced in apolipoprotein E-deficient mice and the group to receive the FIR irradiation was placed in a FIR dry sauna at 41°C for 15 min and then at 34°C for 20 min once daily, with total duration of the experiment of 5 weeks. Laser-Doppler perfusion imaging demonstrated that at the ischemic limb, blood perfusion ratio in the irradiated group increased significantly in comparison with the control group (0.79±0.04 vs. 0.54±0.08, p<0.001). Also, in the treated group, significantly greater capillary density was observed (757±123 per mm2 vs. 416±20 per mm2, p<0.01). Western blotting showed that thermal therapy has increased markedly the hindlimb eNOS expression. Furthermore, to study possible involvement of eNOS in thermally induced angiogenesis, the same FIR therapy was given to mice with hindlimb ischemia with or without N(G)-nitro-L-arginine methyl ester (L-NAME) administration for the duration of 5 weeks. It was observed that L-NAME treatment eliminated angiogenesis induced using the FIR thermal therapy and that the therapy did not increase angiogenesis in eNOS-deficient mice. The study led to the conclusion that angiogenesis can be induced via eNOS using FIR thermal therapy in mice with hindlimb ischemia.

Circular polarizationexample

Far infrared (FIR) radiation (λ = 3–100 μm) is a subdivision of the electromagnetic spectrum that has been investigated for biological effects. The goal of this review is to cover the use of a further sub-division (3– 12 μm) of this waveband, that has been observed in both in vitro and in vivo studies, to stimulate cells and tissue, and is considered a promising treatment modality for certain medical conditions. Technological advances have provided new techniques for delivering FIR radiation to the human body. Specialty lamps and saunas, delivering pure FIR radiation (eliminating completely the near and mid infrared bands), have became safe, effective, and widely used sources to generate therapeutic effects. Fibers impregnated with FIR emitting ceramic nanoparticles and woven into fabrics, are being used as garments and wraps to generate FIR radiation, and attain health benefits from its effects.

FIR emitting garments and fabrics manufactured from fibers impregnated with ceramic nanoparticles (Celliant®, Hologenix, Santa Monica, CA, USA). (A) fibers, (B) yarns, (C) fabrics, (D) knee bandage brace, (E) socks, (F) gloves, (G) elbow bandage brace, (H) multi-purpose bandage, (I) performance apparel, (J) mattress, and (K) puppy blanket.

Ting-Kai Leung and colleagues have studied the effect of FIR-emitting ceramic powders in a range of biological studies [14 –19]. In one set of studies, they cultured murine myoblast cells (C2C12) with bags of ceramic powder under the culture plates and found that FIR irradiation improved cell viability and prevented lactate dehydrogenase release under hydrogen peroxide (H2O2)-mediated oxidative stress, and also elevated the intracellular levels of NO and calmodulin [14]. In the study, they used electro-stimulation of amphibian skeletal muscle and found that FIR emitting ceramics delayed the onset of fatigue, induced by muscle contractions [14]. In another set of studies, they showed that ceramic-emitted FIR (cFIR) could increase the generation of intracellular NO in breast cancer cells [15] and inhibit growth of murine melanoma cells [16]. Similarly, they found that cFIR increased calmodulin and NO production in RAW 264.7 macrophages [17]. cFIR also has been shown to increase the viability of murine macrophages with different concentrations of H2O2 [15]. In this study [15] it was shown that cFIR significantly inhibited intracellular peroxide levels and lipopolysaccharide (LPS)-induced peroxide production by macrophages. In the same study, it was also demonstrated that cFIR blocked ROS-mediated cytotoxicity (shown by measurements of cytochrome c and the ratio of NADP+/NADPH) [15].

All we need to solve these problems are the indices of refraction. Air has n1 = 1.00, water has n2 = 1.333, and crown glass has  n’2  = 1.520. The equation   can be directly applied to find θb in each case.

Rao et al. [40] used garments made out of bioceramic-coated neoprene in conjunction with a “topical cream” to treat cellulite of the legs. Each subject was randomized to receive occlusion by the garment on either the right or left leg, with the contralateral side serving as a control with no occlusion. Of the 17 subjects who completed the study, 76% noticed an overall improvement in their cellulite, with 54 % reporting greater improvement in the thigh that received garment occlusion. Further, the evaluators found the occluded thighs to show greater improvement than the non-occluded thighs in 65 % of subjects. Bioceramic-coated neoprene garment occlusion potentiated the effect of the topical agent in cellulite reduction. A follow up two-center, double-blinded, randomized trial found similar results [41].

We analyzed the peer-reviewed applications of therapeutic FIR delivery systems and realized that there are three main techniques for FIR radiation delivery: i) FIR saunas, ii) FIR ray devices and iii) FIR emitting ceramics and fabrics.

Despite all these different uses of FIR in medical applications, the exact mechanisms of the hyperthermic effects and biological activities of FIR irradiation are still poorly understood. It is clear that two kinds of FIR therapy may exist. The first type (FIR saunas and some FIR generators powered by electricity) uses irradiances or power densities (tens of mW/cm2) that are sufficient to heat up the tissue, while others such as ceramic discs, powders, and fabrics (that use no external power but rely on energy from the body) have such low irradiances that they do not heat the tissue (0.1–5 mW/cm2). The question arises to what extent are the fundamental mechanisms of these two forms of FIR therapy the same, and to what extent are they different ? Furthermore, the question may be posed as to what degree of similarity that FIR therapy has with the reasonably well-established therapy called low level laser (light) therapy (LLLT) also known as photobiomodulation (PBM). Pertinent to this question is the fact that many devices used to deliver therapeutic visible or NIR light were approved by the US Food and Drug Administration as being equivalent to an “ infrared heat lamp ”. The cellular and molecular mechanisms of LLLT/PBM are to some extent understood and involve absorption of red or NIR light by mitochondrial chromophores such as cytochrome c oxidase (CCO, unit IV of the mitochondrial respiratory chain) [43]. This photon absorption activates the enzyme possibly by photo-dissociating the inhibitory molecule, NO, from the copper B (CuB) site [44]. This loss of NO allows electron transport, oxygen consumption, and adenosine triphosphate (ATP) to rapidly increase and results in a marked rise in mitochondrial membrane potential (MMP) that gives rise to a brief burst of ROS [45]. Signaling pathways are activated by ATP, NO, and ROS and these lead to activation of transcription factors (such as NF-κB) [46] that lead to the long-term effects on tissue (healing, anti-inflammatory and pain relief [47]) seen after relatively transient periods of illumination.

Keywords: far infrared radiation, radiant heat, blackbody radiation, biogenetic rays, FIR emitting ceramics and fibers, infrared sauna

Light reflected at these angles could be completely blocked by a good polarizing filter held with its axis vertical. Brewster’s angle for water and air are similar to those for glass and air, so that sunglasses are equally effective for light reflected from either water or glass under similar circumstances. Light not reflected is refracted into these media. So at an incident angle equal to Brewster’s angle, the refracted light will be slightly polarized vertically. It will not be completely polarized vertically, because only a small fraction of the incident light is reflected, and so a significant amount of horizontally polarized light is refracted.

Discs and garments manufactured of FIR emitting ceramic material have been applied to the human body (Figure 5). For instance, a blanket containing discs has been reported to improve quality of sleep [34] and single discs were applied to the breasts of women who encountered difficulty in producing sufficient breast milk during lactation [35]. Gloves have been made out of FIR emitting fabrics and there have been reports that these gloves can be used to treat arthritis of the hands and Raynaud’s syndrome [36].

In their recent clinical study, Liau et al. [39] looked into the benefits of using an FIR emitting belt for managing the discomfort of primary dysmenorrhea in female patients. Taking into account several parameters, such as body temperature, abdominal blood flow, pain assessment, and heart rate variability, they showed that FIR belts used increased the local surface body temperature as well as the abdominal blood flow; in addition to reducing the pain and the discomfort from it. In this particular study, a THERMEDIC FIR belt (LinkWin Technology Co., Ltd., Taiwan) with the capability to generate 11.34 mW/ cm2 at 50°C was used.

12: Light reflected at 55.6o from a window is completely polarized. What is the window’s index of refraction and the likely substance of which it is made?

Small particles (nanoparticles and microparticles) of FIR-emitting ceramic material have been incorporated into fibers that are then woven into fabrics. These fabrics can be manufactured into various garments that can be worn on different parts of the body.

Another interesting phenomenon associated with polarized light is the ability of some crystals to split an unpolarized beam of light into two. Such crystals are said to be birefringent (see Figure 15). Each of the separated rays has a specific polarization. One behaves normally and is called the ordinary ray, whereas the other does not obey Snell’s law and is called the extraordinary ray. Birefringent crystals can be used to produce polarized beams from unpolarized light. Some birefringent materials preferentially absorb one of the polarizations. These materials are called dichroic and can produce polarization by this preferential absorption. This is fundamentally how polarizing filters and other polarizers work. The interested reader is invited to further pursue the numerous properties of materials related to polarization.

Polaroid sunglasses are familiar to most of us. They have a special ability to cut the glare of light reflected from water or glass as shown in the figure below.  Polaroids have this ability because of a wave characteristic of light called polarization. What is polarization? How is it produced? What are some of its uses? The answers to these questions are related to the wave character of light.

A belt containing FIR-emitting sericite mineral (a fine grained mica) was used to study the relief of menstrual pain [38]. In this study, 104 patients with primary dysmenorrhea were randomized to wear a sericite or placebo belt during sleep for three menstrual cycles, and then followed up for two additional menstrual cycles with no belt. Hot packs were used to heat the ceramics and ensure slight pain relief in both groups. Although the severity of dysmenorrhea decreased during the treatment period in both groups, it was found that during the follow-up period, the decreased VAS (pain) score was maintained in the experimental group, whereas the VAS score gradually returned to baseline in the control group, which resulted in significant difference between the groups (p = 0.0017).

Polarizing filters have a polarization axis that acts as a slit. This slit passes electromagnetic waves (often visible light) that have an electric field parallel to the axis. This is accomplished with long molecules aligned perpendicular to the axis as shown in Figure 9.

The classification of the International Commission on Illumination (CIE) has three sub-divisions for the IR radiation as given in Table 1. An alternative classification provided in ISO 20473 standard for the sub-division of the IR ranges is given in Table 2.

6: Show that if you have three polarizing filters, with the second at an angle of 45o to the first and the third at an angle of 90.0o to the first, the intensity of light passed by the first will be reduced to 25.0% of its value. (This is in contrast to having only the first and third, which reduces the intensity to zero, so that placing the second between them increases the intensity of the transmitted light.)

FIR sauna. (A, B) Comparison of FIR sauna with conventional heated sauna. (C) Cabin incorporating FIR emitting “cold” unit(s) (Anhui Hi-Tech Electronic Commerce Co., Ltd., Hefei, China).

Fatma Vatansever, Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; and Department of Dermatology, Harvard Medical School, Boston, MA, USA.

FIR emitting ceramics have been known for some time [9, 10]. All ceramics have the property of emitting IR radiation depending on their temperature. In the age of gas lighting, ceramic mantles were heated by gas flames to emit both IR and visible radiation depending on the temperature attained. The exact chemical composition of the ceramic material governs the relationship between the temperature and the amount of IR radiation. The radiated energy follows the Stefan-Boltzmann law which says that the total energy radiated per unit of surface area per unit of time is directly proportional to the fourth power of the black body’s absolute temperature. The wavelength range also depends strictly on the temperature according to Wien’s displacement law [11].

The same research group went on to study a rabbit model of rheumatoid arthritis in which rabbits received intra-articular injections of LPS to induce inflammation that mimics the rheumatoid arthritis [18]. Fluorodeoxyglucose(18F) coupled with positron emission tomography (FDG-PET) scans were used to monitor the inflammation in 16 h and 7 days after the LPS injection. Rabbits to be treated with cFIR were placed in a cage surrounded by paper sheets impregnated with a thin layer of the ceramic powder, while the control group was surrounded by the same sheet without the material. Comparison of the final and initial uptakes of FDG isotopes in the LPS-injected left knee-joints of the rabbits indicated larger decreases in the cFIR exposed group than in the control group indicating that FIR reduced inflammation.

Circular polarization

There is a range of optical effects used in sunglasses. Besides being Polaroid, other sunglasses have coloured pigments embedded in them, while others use non-reflective or even reflective coatings. A recent development is photochromic lenses, which darken in the sunlight and become clear indoors. Photochromic lenses are embedded with organic microcrystalline molecules that change their properties when exposed to UV in sunlight, but become clear in artificial lighting with no UV.

Photographs of the sky can be darkened by polarizing filters, a trick used by many photographers to make clouds brighter by contrast. Scattering from other particles, such as smoke or dust, can also polarize light. Detecting polarization in scattered EM waves can be a useful analytical tool in determining the scattering source.

Light is one type of electromagnetic (EM) wave. As noted earlier, EM waves are transverse waves consisting of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation (see Figure 2). There are specific directions for the oscillations of the electric and magnetic fields. Polarization is the attribute that a wave’s oscillations have a definite direction relative to the direction of propagation of the wave. (This is not the same type of polarization as that discussed for the separation of charges.) Waves having such a direction are said to be polarized. For an EM wave, we define the direction of polarization to be the direction parallel to the electric field. Thus we can think of the electric field arrows as showing the direction of polarization, as in Figure 2.

Figure 6 shows the effect of two polarizing filters on originally unpolarized light. The first filter polarizes the light along its axis. When the axes of the first and second filters are aligned (parallel), then all of the polarized light passed by the first filter is also passed by the second. If the second polarizing filter is rotated, only the component of the light parallel to the second filter’s axis is passed. When the axes are perpendicular, no light is passed by the second.

17: (a) 2.07 x10-2 o C/s (b) Yes, the polarizing filters get hot because they absorb some of the lost energy from the sunlight.

There have been many attempts to use FIR as a therapeutic intervention where devices known as “infrared heat lamps” that emit more or less FIR are been used. Unfortunately, “ pure ” FIR emitting lamps are expensive, and thus, in some instances lamps that have “mixed” emission, i.e., emit in shorter (mid infrared, MIR; near infrared, NIR and even visible light) wavelength ranges are been used. A common type of specialized infrared heat lamp emits 2–25 μm radiation. IR saunas are often used and the most effective types have ceramic FIR emitting panels that remain cool to the touch. However, most IR saunas on the market do not use the expensive FIR panels, which can be touched since they remain always cold.

Suppose you put on two pairs of Polaroid sunglasses with their axes at an angle of 15.0o. How much longer will it take the light to deposit a given amount of energy in your eye compared with a single pair of sunglasses? Assume the lenses are clear except for their polarizing characteristics.

All living organisms are subjected to the natural electromagnetic radiation reaching the earth from the sun. Living organisms experience the beneficial as well as adverse effects of it at all levels, starting from sub-cellular organelles and ending with the whole body. Thermal radiation (or infrared) is a band of energy in the complete electromagnetic spectrum and it has been used effectively for millennia to treat/ease certain maladies and discomforts. Heated saunas are only one of the avenues (and perhaps the oldest) to deliver the radiation in a controlled environment and within a convenient treatment time. With the development of better technology to deliver pure far infrared radiation (FIR), the benefits from its effects have widened. Nowadays, specialty FIR emitting heat lamps and garments made up of filaments (fibers) impregnated with FIR emitting nanoparticles are becoming used to deliver these thermal radiation effects. In this paper we explore the use of FIR as a promising treatment modality for certain medical conditions. We cover both traditional applications and novel applications, and survey the latest technological advancements and most recent scientific studies in the field.

Common devices are WS TY-101N® and WS TY-301R® (made by WS Far Infrared Medical Technology Co., Ltd., Taipei, Taiwan; see Figure 3). A report from Hu and Li [31] describes the treatment of allergic rhinitis. A WS TY-101N® FIR emitter was placed 30 cm from the patient’s nasal region. The treatment was performed for 40 min every morning for 7 days. Every day, patients recorded their symptoms in a diary before and during treatment. Each symptom of rhinitis was rated on a 4-point scale (0–3) according to severity. During the period of FIR therapy, the symptoms of eye itching, nasal itching, nasal stuffiness, rhinorrhea, and sneezing were all significantly improved. Smell impairment was improved after the last treatment. Lin et al. [32] used a WS TY-101N® FIR emitter to treat vascular access malfunction with an inadequate access flow (Qa) in hemodialysis (HD) patients. This randomized trial demonstrated that FIR therapy could improve access flow and potency of the native arteriovenous fistula (AVF) in a total of 145 HD patients (73 in the control group and 72 in the FIR-treated group). FIR was used for 40 min, and hemodynamic parameters were measured by the HD02 monitor (M/s Transonic System Inc.), during the hemodialysis. In comparison with control subjects, patients who received FIR therapy for 1 year had a lower incidence (12.5 vs. 30.1%; p<0.01) and relative incidence (one episode per 67.7 vs. one episode per 26.7 patient-months; p = 0.03) of AVF malfunction. Hausswirth et al. [33] showed that FIR therapy reduced symptoms of exercise-induced muscle damage in athletes after a simulated trail running race.

Celliant® (Hologenix, Santa Monica, CA, USA) is a polyethylene terephthalate (PET) fiber that incorporates FIR emitting ceramic nanoparticles. York and Gordon [42] studied socks manufactured from Celliant® fiber material in patients with chronic foot pain resulting from diabetic neuropathy or other disorders. A double-blind, randomized trial with 55 subjects (38 men, 17 women, average age 59.7 ± 11.9 years) enrolled 26 patients with diabetic neuropathy and 29 with other pain etiologies. Subjects twice completed the VAS, brief pain inventory (BPI), McGill pain questionnaire (MPQ), and a multipurpose, short form health survey with 36 questions (SF-36) a week apart [W(1+2)] before receiving either control or Celliant® socks. The same questionnaires were answered again 1 and 2 weeks later [W(3+4)]. The questionnaires provided nine scores for analyzing pain reduction: one VAS score, two BPI scores, five MPQ scores, and the bodily pain score on the SF-36. Mean W(1+2) and W(3+4) scores were compared to measure pain reduction. More pain reduction was reported by Celliant® subjects for eight of the nine pain questions employed, with a significant (p = 0.043) difference between controls and Celliant® for McGill question III. In neuropathic subjects, Celliant®; caused greater pain reduction in six of the nine questions, but not significantly. In non-neuropathic subjects eight of nine questions showed better pain reduction with the Celliant® socks.

(a) At what angle will light traveling in air be completely polarized horizontally when reflected from water? (b) From glass?

A fairly large angle between the direction of polarization and the filter axis is needed to reduce the intensity to 10.0% of its original value. This seems reasonable based on experimenting with polarizing films. It is interesting that, at an angle of 45o, the intensity is reduced to 50% of its original value (as you will show in this section’s Problems & Exercises). Note that 71.6o is 18.4o from reducing the intensity to zero, and that at an angle of 18.4o the intensity is reduced to 90.0% of its original value (as you will also show in Problems & Exercises), giving evidence of symmetry.

Corresponding author: Michael R. Hamblin, Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA, hamblin@helix.mgh.harvard.edu

Michael R. Hamblin, Department of Dermatology, Harvard Medical School, Boston, MA, USA; and Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, USA.

Glass and plastic become optically active when stressed; the greater the stress, the greater the effect. Optical stress analysis on complicated shapes can be performed by making plastic models of them and observing them through crossed filters, as seen in Figure 14. It is apparent that the effect depends on wavelength as well as stress. The wavelength dependence is sometimes also used for artistic purposes.

Polarization of light notes PDF

4: What angle would the axis of a polarizing filter need to make with the direction of polarized light of intensity 1.00 kW/m2 to reduce the intensity to 10.0W/m2?

3: If you have completely polarized light of intensity 150 W/m2 what will its intensity be after passing through a polarizing filter with its axis at an 89.0o angle to the light’s polarization direction?

3: No light passes through two perfect polarizing filters with perpendicular axes. However, if a third polarizing filter is placed between the original two, some light can pass. Why is this? Under what circumstances does most of the light pass?

If it can be proved that non-heating FIR has real and significant biological effects, then the possible future applications are wide ranging. Not only could bandages and dressings made out of NIR emitting fabrics be applied for many medical conditions and injuries that require healing, but there is a large potential market in lifestyle enhancing applications. Garments may be manufactured for performance enhancing apparel in both leisure activities and competitive sports areas. Cold weather apparel would perform better by incorporating FIR emitting capability and sleeping environments could be improved by mattresses and bedding emitting FIR.

The Sun and many other light sources produce waves that are randomly polarized (see Figure 4). Such light is said to be unpolarized because it is composed of many waves with all possible directions of polarization. Polaroid materials, invented by the founder of Polaroid Corporation, Edwin Land, act as a polarizing slit for light, allowing only polarization in one direction to pass through. Polarizing filters are composed of long molecules aligned in one direction. Thinking of the molecules as many slits, analogous to those for the oscillating ropes, we can understand why only light with a specific polarization can get through. The axis of a polarizing filter is the direction along which the filter passes the electric field of an EM wave (see Figure 5).

13: (a) Light reflected at 62.5o from a gemstone in a ring is completely polarized. Can the gem be a diamond? (b) At what angle would the light be completely polarized if the gem was in water?

Only the component of the EM wave parallel to the axis of a filter is passed. Let us call the angle between the direction of polarization and the axis of a filter θ. If the electric field has an amplitude E, then the transmitted part of the wave has an amplitude Ecosθ (see Figure 7). Since the intensity of a wave is proportional to its amplitude squared, the intensity I of the transmitted wave is related to the incident wave by

The boron-silicate mineral, tourmaline (known as a gemstone in its crystalline form) when milled into fine powders also emits FIR [12] and the characteristics of the FIR emission depend on the particle size. Preparations containing tourmaline powder have been applied to the skin with the aim of affecting the blood flow [13]. In a similar manner discs of FIR emitting ceramics have been attached to the skin with the intent of producing a beneficial effect (see later).

When FIR emitting ceramics or fabrics are employed as therapeutic devices, it is pertinent to analyze the thermodynamics of the process. The first law of thermodynamics states that energy can neither be created nor destroyed. Heat (molecular vibrational energy) is transferred from one body to another in three forms: radiation, convection and conduction. Thus, it is clear that the principle source of energy needed to power the FIR emission from the garments comes from the human body, since it is at a significantly higher temperature than the surrounding air. So energy from the human body is transferred to these ceramic particles, which are acting as “perfect absorbers”, maintain their temperature at sufficiently high levels and then emit FIR back to the body. It is plausible that FIR emitted from the skin is absorbed by the ceramic particles, which then re-emit the same FIR back to the skin. Although this may appear to be an energy neutral process and to cancel itself out, this is not in fact the case because the FIR emitting material will prevent the loss of FIR that would otherwise have escaped through normal clothing. However the same effect could have been achieved with a FIR reflective foil suit or suchlike. Other sources of heat that can transfer energy from the body to the ceramic particles with a net gain of FIR are either convection, conduction, or both. The balance between conduction and convection will depend on how close the contact is between the garment and the skin. If the garment is skin tight, then conduction may be important, while if it is loose fitting then convection (heating up a layer of air between the skin and the garment) may be important.

Figure 10 illustrates how the component of the electric field parallel to the long molecules is absorbed. An electromagnetic wave is composed of oscillating electric and magnetic fields. The electric field is strong compared with the magnetic field and is more effective in exerting force on charges in the molecules. The most affected charged particles are the electrons in the molecules, since electron masses are small. If the electron is forced to oscillate, it can absorb energy from the EM wave. This reduces the fields in the wave and, hence, reduces its intensity. In long molecules, electrons can more easily oscillate parallel to the molecule than in the perpendicular direction. The electrons are bound to the molecule and are more restricted in their movement perpendicular to the molecule. Thus, the electrons can absorb EM waves that have a component of their electric field parallel to the molecule. The electrons are much less responsive to electric fields perpendicular to the molecule and will allow those fields to pass. Thus the axis of the polarizing filter is perpendicular to the length of the molecule.