Things About Low-e Glass

things about low e glass

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Glass Products Types

There are mainly tempered glass, semi-tempered/heat-strengthened glass, laminated glass, coated glass, double glazing, and different combinations of them. For example, tempered coated insulating glass, coated laminated insulating glass, etc.

About SC

SC (Shading Coefficient): the ratio of solar radiation energy through the glass to solar radiation energy through 3mm clear glass under the same conditions. The solar radiation energy through 3mm clear glass is 630w/m2.

SC = direct solar radiation energy ÷ 630 w/m2
Direct solar radiation energy = 630 w/m2 × SC.

The shading coefficient reflects the heat transfer of direct solar radiation through the glass.

Higher or Lower SC?

Glasses with different shading coefficients are suitable for different climatic regions.

A high shading coefficient allows more solar radiation to enter the room through the glass window, thus reducing the heating cost in winter. This type of glass is suitable for use in northern regions with long winters.
Low shading coefficient, good blocking effect on direct solar radiation, which can reduce the direct solar radiation energy entering into the room. This kind of glass is suitable for use in the southern region with long summer.

U Value

U value reflects the heat energy transmitted through the glass due to convection conduction, which includes the transmission of heat energy absorbed by the glass and then radiated to the outside. Therefore, the emissivity E of the glass is low, and the U-value is correspondingly low. Convection transfer heat energy = U value × (Tout – Tin) Tout & Tin are outdoor and indoor temperature respectively.

Total Heat Energy Transfer

It consists of two parts: direct solar heat transfer and convective heat transfer. It is expressed by the formula: Q total = 630 × Sc + U × (Tout – Tin)

Solar Radiation Compositions

It consists of three parts: ultraviolet radiation, wavelength range 0.01 to 0.38 microns.

Visible light wavelength range 0.38 to 0.75 microns. Near-infrared radiation, wavelength range 0.75 to 3 microns.

Far-infrared thermal radiation

Far infrared heat radiation is indirectly from the sun, this part of the energy is thermal energy, is irradiated by the sun to the object is absorbed by the object and then radiation, its wavelength range distribution in 3 ~ 40 microns.

In summer, the far-infrared heat radiation emitted from outdoor roads and buildings under sunlight is one of the main heat sources from outdoor.

Is there far-infrared heat radiation indoors

Yes, far-infrared heat radiation indoors comes from heaters, household appliances, furniture irradiated by sunlight, fireplaces, and the human body, and is the main heat source from indoors in winter.

How does far-infrared heat radiation pass through glass?

Far-infrared heat radiation cannot directly transmit through ordinary glass, but can only be absorbed or reflected by the glass.

The glass absorbs this part of the energy, the temperature will rise, and through the convection and air conduction to both sides and then send out thermal radiation and dissipate this part of the energy, so this part of the energy is ultimately through the glass, but first absorbed and then radiated through the way.

How to distinguish Far-infrared heat radiation and Near-infrared radiation?

Near-infrared radiation comes directly from the sun, and its heat sensation is not obvious, but it can be converted into heat after being absorbed by objects.

Far-infrared heat radiation, as a result of solar energy conversion or artificial production, is heat itself.

When observing a road under the sun in summer, you can see waves of heat radiation rising from the ground (i.e. solar energy is being converted into heat radiation).

In winter, when you are near a heater, you can feel the heat radiation directly.

What is Low-E glass?

Low-E glass is formed by coating the glass surface so that the emissivity E of the glass is reduced from 0.84 to less than 0.15.

Characteristics of Low-E Glass

Low-E glass has the following characteristics:

★ High infrared reflectivity, which can directly reflect far-infrared heat radiation.

★ Low surface emissivity E, which absorbs little external energy and thus re-radiates less thermal energy.

★ Wide range of shading coefficient Sc, which can control the amount of solar energy transmission according to the need to adapt to the needs of different regions.

Why Low-E can reflect heat?

The Low-e film layer is coated with silver, which can reflect more than 98% of the far-infrared heat radiation, thus directly reflecting heat like a mirror reflects light.

Low-E shading coefficient can range from 0.2 to 0.7 so that the direct solar energy entering the room can be regulated according to needs.

What is heat reflective glass?

Heat-reflective glass is commonly known as coated glass, which is formed by coating the glass surface so that the shading coefficient Sc of the glass is reduced from 0.98 (6mm clear glass) to 0.2 to 0.6.

Difference between heat-reflective glass and Low-e glass?

Heat-reflective glass is to reduce the shading coefficient of glass to limit the direct solar radiation through the glass into the room, so as to reduce air conditioning costs and save energy.

Low-E glass is to reduce the U-value of glass to limit the far-infrared heat radiation through the glass, so as to reduce the convective heat transfer through the glass. At the same time Low-E glass shading coefficient Sc adjustment range is large, can be effective control of the direct solar radiation into the room.

Coating Technology

Online coating and Offline coating

Online coating glass is manufactured on a float glass production line, which has a single variety of glass, poor heat reflection properties, and low manufacturing costs. Its only advantage is that it can be processed by heat bending. Window and door empire, the largest free resource platform for the window and door industry.

The coated glass manufactured by the vacuum magnetron sputtering process is colorful, with excellent heat-reflective properties and obvious energy-saving characteristics. 

Can Low-E glass used as a single piece?

Low-E glass made by vacuum magnetron sputtering process can not be used as a single piece, but only synthetic insulating glass or laminated glass.

However, its emissivity E is much lower than 0.15 and can be as low as 0.1 or less.

Low-E glass manufactured by the in-line coating process can be used in a single piece.

But its emissivity E = 0.28, which strictly speaking can no longer be called Low-E glass (scientifically speaking, objects with emissivity E £ 0.15 are called low-emitting objects). low-E glass is most effective in the similarly closed space formed in sealed insulating glass, because this closed space eliminates the Low-E surface airflow, thus allowing Low-E glass to function better.\

Does Low-E glass perform the same?

From a technical standpoint, all Low-E glass is treated in the same way for spectral curves, but not all perform the same.

Do all Low-E glasses look the same?

No! Some Low-E appears to be highly transparent, with transmittance above 60%, and light in color. Some Low-E looks less transparent, with transmittance below 55%, and is relatively dark.

Does Low-E glass still work at night?

Yes! Low-E glass works both day and night. In winter, the heat (far-infrared heat radiation) is reflected back into the room both day and night, because both the heat generated by heating and the heat converted from solar energy is in the form of far-infrared heat radiation.

How does Low-E glass work in summer and winter?

In winter, the indoor temperature is higher than the outdoor temperature, and the far-infrared heat radiation mainly comes from the indoor, and Low-E glass can reflect it back to the indoor to keep the indoor heat from escaping. For some solar radiation from outside, Low-E glass can still allow it to enter the room, and this part of the energy is absorbed by indoor objects and then transformed into far-infrared heat radiation and left indoors.

In summer, the outdoor temperature is higher than the indoor, far-infrared heat radiation mainly from outdoor, Low-E glass can reflect it out to prevent heat into the room. For solar radiation from outside, Low-E glass with a low shading coefficient can be chosen to limit its entry into the room, thus reducing the cooling cost (air conditioning cost).

On which surface of IGU is the Low-e layer most suitable?

Insulating glass has 4 surfaces, #1, #2, #3, and #4, counting from outside to inside.

In areas where the heating demand exceeds the cooling demand (northern areas), the Low-E film layer is located on surface #3.

Conversely, in areas where the cooling demand exceeds the heating demand (southern areas), the Low-E film layer should be located on surface #2.

What is the role of argon gas in IGU?

Argon is an inert gas, its heat transfer is worse than air, so it can reduce the U-value of insulating glass and increase the heat insulation of insulating glass when filled into the insulating glass.

For Low-E insulating glass, argon gas also has the function of protecting the Low-E film layer.

The negative effect of ultraviolet light

UV is short-wave radiation, invisible to the naked eye, and it accounts for about 2% of the total energy of solar radiation. UV radiation can kill bacteria, but prolonged exposure can burn human skin and eyes, and can also cause furniture and clothing to fade.

How much UV light can Low-E glass attenuate?

Low-E glass reduces UV light by 25% compared to ordinary single-piece clear glass. Low-E glass cannot completely prevent fading of furniture, but it can slow it down.

Effect of Low-E glass on indoor plants

There is no adverse effect on most common plants. For the effect on special and rare plants, please consult the relevant florist.

Do shades, trees and awnings affect the performance of Low-e glass?

These objects limit the amount of heat and light entering the room through the window, i.e., they block some solar energy from passing through, but they do not affect the performance of Low-E glass.

Which direction is the best to install Low-E glass?

In winter, no matter which direction Low-E glass is facing, it does not affect its performance because it mainly reflects the heat of the room.

However, the best effect is to install it facing north, after all, Low-E glass prevents indoor heat dissipation and also restricts solar radiation more or less.

In summer, Low-E mainly reflects outdoor heat, so it is suitable to install it facing either direction, but the best effect is to install it facing east, west and south because it can also reduce the solar energy transmission.

How long does the Low-e layer last?

The duration of its coating layer is the same as the duration of the insulating glass space layer seal.

What is the effect of combining Low-E glass with tinted glass?

There are three combinations: Low-E coating on tinted glass, insulating glass with tinted glass, and laminated glass with tinted glass.

Tinted glass further reduces the shading factor of the combined glass product, thus limiting more direct solar radiation into the room.

Therefore, the combined use of these three ways is very effective and more suitable for use in the southern temperate tropics.

Combined use with tinted glass can also greatly increase its decorative effect.


Low-e glass is essential not only for windows and doors but only widely used for commercial building facades,  canopies, roofs, blinds systems. Wherever solar control and energy-saving needed places. 

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