How much ultraviolet light can Low-E glass attenuate?

Ultraviolet (Ultraviolet), also known as ultraviolet radiation (sometimes referred to as UV), was discovered in the early 19th century and generally refers to light radiation with a wavelength of 100nm to 380nm. According to the different wavelengths, it can be divided into three types: long-wave ultraviolet (UltravioletA, UVA, wavelength 315nm～380nm), medium-wave ultraviolet (UVB, wavelength 280nm～315nm), and short-wave ultraviolet (UVC, wavelength 200nm～280nm). Ultraviolet radiation is a double-edged sword to human life. We cannot do without it, and there will be the harm in excess.

As people's requirements for the energy-saving performance of doors and windows increase, Low-E glass is more and more widely used, but people are more concerned about the blocking effect of Low-E glass on infrared radiation, and seldom care about its attenuation of ultraviolet rays. This article introduces the effects and effects of ultraviolet rays on the human body and objects, discusses the attenuation of Low-E glass to ultraviolet rays, and gives suggestions on whether it is necessary to consider the attenuation of ultraviolet rays when choosing Low-E glass.

The role and influence of ultraviolet light

In sunlight, ultraviolet radiation with a wavelength below 300 nm is almost completely absorbed by the atmosphere. The ultraviolet radiation reaching the surface generally only contains components with a wavelength of 300 nm to 380 nm, namely UVA and part of UVB. Almost all UVCs that can be touched in daily life come from lightning or artificial light sources, which are beyond the scope of this chapter.

1.1 The role and impact on human health

An appropriate amount of ultraviolet rays irradiate the human body, which has certain benefits to the human body, and the appropriate amount of UVB can promote the production of vitamin D. However, the human body is exposed to excessive ultraviolet radiation, which will cause a series of changes in the body, causing harm to human eyes, skin, immune system, etc. UVA can be absorbed by the lens, causing lens damage and causing non-congenital cataracts. In addition, excessive ultraviolet radiation can cause damage to the retinal macular area, cause macular degeneration, and even cause vision loss. The main components of ultraviolet rays that cause skin damage are UVA and UVB. Long-term exposure to ultraviolet rays can cause skin erythema, swelling and pain, itching, thickening of the epidermis, pigmentation, and photoaging, and even skin tumors. The skin is an important immune organ and the human body’s first line of defense. Ultraviolet rays can damage the skin and cause a series of inflammations, which reduce the body’s ability to resist external invasions. It also inhibits the vitality of immune cells and reduces human immunity.

Sun protection tips: Sunglasses should be worn outdoors in strong sunlight. In the case of long outdoor activities, eat less or no "photosensitive" vegetables and fruits, such as spinach and mango.

1.2 Impact on bamboo and wood materials

Bamboo and wood materials and their products are the most basic materials used in people's daily life. They are widely used in interior decoration, furniture, flooring, etc., and are also the basic raw materials for paper products such as books, calligraphy, and painting. The main components of bamboo and wood materials such as cellulose and hemicellulose absorb ultraviolet rays to a certain extent. After absorption, the molecular structure will be damaged to varying degrees, and its physical and chemical properties will also be seriously affected, which ultimately affects the stability of bamboo and wood materials. Performance, durability, aesthetics, etc. Cellulose can absorb light in the entire ultraviolet band, and the absorption tailband can be extended to 400nm [4], that is, UVA and UVB have different degrees of absorption, resulting in the phenomenon of cellulose aging, and hemicellulose has an effect on light energy. The absorption characteristics of cellulose are similar to those of cellulose.

1.3 Impact on polymer materials

Polymer materials include plastics, rubber, fibers, films, adhesives, and coatings, etc., which are widely used in indoor furniture and installations. When polymer materials are irradiated with light, the molecular chains of the materials are broken, the physical and mechanical properties have deteriorated, and the chemical structure is changed, thereby partially losing or losing its use-value, and appearing hard, sticky, brittle, discolored, and losing strength. It is the photo-aging of polymers. The shorter the light wave, the greater the energy of the light. It can be seen from Table 1 that the energy of ultraviolet radiation is generally higher than the energy required to cause chemical bond breakage, which can cut the chemical bond of most polymer materials. In addition, the actual use environment of polymer materials is mostly The presence of oxygen will also accelerate the photoaging process.

^{Table 1 Chemical bond energy and ultraviolet wavelength of similar energy}

Common glass attenuation of ultraviolet rays

The GlassSpec2500 building glass sunlight band spectrophotometer is used to measure the ultraviolet transmission of common glass. The measuring wavelength range of this instrument is 300nm～2500nm. It can directly measure the ultraviolet transmittance of hollow glass without destroying the hollow glass structure and has spectral data export. The function can meet the measurement requirements, the appearance of the instrument is shown in Figure 1.

^{Figure 1 GlassSpec2500 architectural glass sunlight band spectrophotometer}

2.1 Attenuation of ordinary architectural glass to ultraviolet rays

Ultraviolet transmission measurement of double-glass insulating glass made of ordinary and ultra-white float glass. The glass structures are (6mmClear+12Air+6mmClear) and (6mmSuperClear+12Air+6mmSuperClear). Table 2 shows the UV spectrum data derived from the instrument.

^{Table 2 Ultraviolet spectrum data of ordinary insulating glass and ultra-white insulating glass}

The instrument provides the ultraviolet transmittance of ordinary insulating glass and ultra-white insulating glass, and the surveyor calculated the transmittance of solar ultraviolet A band and solar ultraviolet B band according to the data in Table 2. The results are shown in Table 3. The ultraviolet transmittance of ordinary insulating glass is 47.44%, which can attenuate about 52.56% of ultraviolet rays. Ultraviolet rays less than 315nm (UVB) can hardly pass through ordinary insulating glass. In fact, consulting the glass database shows that ultraviolet rays in the UVB band are almost impossible. Through an ordinary single white glass, the UVB transmittance of ordinary single white glass is about 0.4%. Therefore, we can think that almost all ultraviolet rays passing through ordinary white glass are UVA, so when considering the effect of ultraviolet rays passing through ordinary white glass and coated glass based on ordinary white glass, there is no need to consider the effect of UVB. For example, the beneficial effects of UVB on health cannot be obtained indoors. If we stand in front of the window and bask in the sun, we cannot achieve the purpose of synthesizing vitamin D, thereby promoting the absorption of calcium, and UVB's damage to indoor items does not need to be considered.

Ultra-white insulating glass has an ultraviolet transmittance of 75.52%, which can attenuate about 24.48% of ultraviolet rays. Most of the transmitted ultraviolet rays are UVA and also contain a certain amount of UVB, which will not completely block UVB. When considering the transmission of ultra-white When the influence of ultraviolet rays of hollow glass is concerned, the influence of UVA and UVB needs to be considered.

^{Table 3 Ultraviolet transmittance of ordinary hollow glass and ultra-white hollow glass}

2.2 Low-E glass attenuation of ultraviolet rays

Measure single-silver, double-silver, and triple-silver Low-E insulating glass (structure 6mmLow-E+12Air+6mmClear) and export the corresponding ultraviolet spectrum data. The spectrum data is shown in Table 4.

^{Table 4 UV spectrum data of different Low-E insulating glass}

The instrument gives the UV transmittance of single silver hollow, double silver hollow, and triple silver hollow, and the surveyor calculated the solar ultraviolet A-band and solar ultraviolet B-band transmittance according to the data in Table 4. The results are shown in Table 5. The UV transmittance of Low-E insulating glass is roughly within 40%, that is, Low-E insulating glass can attenuate more than 60% of ultraviolet rays, which is consistent with the results given by experts in the industry. It's all UVA. Of course, the glass samples selected in this article do not represent all the insulating glass. The data in Table 3 and Table 5 are for reference only.

^{Table 5 UV transmittance of different Low-E insulating glass}

The UV spectrum transmittance data of all the glass samples in this article are summarized, and Figure 2 is obtained. It can be seen from Figure 2 that the attenuation ability of ultraviolet rays is ranked from strong to weak: three silver hollow> double silver hollow> single silver hollow> ordinary hollow> super white hollow. Compared with ultra-white insulating glass and ordinary insulating glass, Low-E insulating glass can attenuate more ultraviolet rays and reduce the incidence of ultraviolet rays into the room to a certain extent.

^{Figure 2 UV spectral transmittance of different insulating glass}

From the above analysis, it can be seen that single silver, double silver, and triple silver hollows with the same structure have different attenuation of ultraviolet rays. Why does this happen? Because the material of Low-E film is a metal or a conductive compound, such a material has a high density of free electrons, and its response to the light field (light is an electromagnetic wave, which generates an electromagnetic field) is related to the frequency of the light field. At low (longwave), the free electrons in the material will be accelerated by the electric field and collide, a small part of the light energy will be absorbed, and the polarized free electrons have a strong electromagnetic shielding effect on the light field, that is, the material is in the infrared The area has a high reflectivity. As the frequency of light increases, the absorption of light energy by the material increases, and the reflectivity of light decreases. Until the light frequency increases to a certain frequency, due to the existence of electronic inertia, the electrons can no longer follow the change of the light field. At this time, the absorption and reflection of light by free electrons are very weak, and light can be transmitted through the material, that is, the material It is already “transparent” to the light above this frequency, but in practical applications, we can change the transmittance of each waveband of the Low-E film by changing the thickness of the Low-E film, and then change the Low-E film. Low-E film attenuation of ultraviolet rays, the thicker the Low-E film, the stronger the attenuation of ultraviolet rays, that is, the attenuation of the Low-E film on ultraviolet rays is positively correlated with the film thickness.

^{The Insulating glass or Low-E glass to ultraviolet rays 1}

Some data show that silver has a high transmission and low attenuation to ultraviolet rays below 350nm, but the attenuation of Low-E glass to ultraviolet rays can be enhanced by increasing the thickness of the silver film. Therefore, in general, Low-E hollow glass has stronger attenuation of ultraviolet rays than ordinary hollow or ultra-white hollow, and triple silver hollow Low-E glass has stronger attenuation of ultraviolet rays, followed by double silver, and single silver is weaker.

Is it necessary to consider the attenuation of Low-E glass to ultraviolet rays?

Whether it is necessary to consider the UV attenuation of Low-E glass is related to the function of the building and the people and facilities inside.

For example: For ordinary residences, when indoor bamboo and wood materials and polymer materials (plastics, coatings, etc.) are used frequently, attention should be paid to the attenuation of ultraviolet rays when choosing Low-E glass, and the ultraviolet rays entering the room should be minimized. Many people worry that too few ultraviolet rays entering the room will reduce the benefits of the human body from ultraviolet radiation. In fact, except for the use of ultra-white original non-Low-E glass hollow glass, we cannot get UVB radiation indoors, that is Basking in the sun in front of indoor glass windows is far less effective than outdoors. The only ultraviolet radiation that can pass through Low-E glass is UVA. In the current scientific understanding, UVA has not found its direct benefits to the human body. That is, no matter how much Low-E glass attenuates ultraviolet rays, the human body cannot Benefits are obtained from the ultraviolet radiation passing through the glass. Some people say that too little ultraviolet rays entering the room can not play a role in sterilization. In fact, the UVC band that can kill bacteria and viruses is mainly in the UVC band, but the sunlight that reaches the surface does not have the UVC band. The short-wave part of UVB also has a sterilization effect. However, judging from the ultraviolet radiation transmission curve of various glasses, except for ultra-white hollow, the band that can play a role in sterilization is blocked by the glass, that is, no matter how much Low-E glass attenuates ultraviolet rays, the ultraviolet rays passing through the glass Neither can play a role in disinfection and sterilization.