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Common Glass Questions

Safety Glass Questions

Low-E Glass Questions


How is glass produced?

Almost all glass produced today in the developed countries is done so by the “float process”. The glass composition materials, mainly silica sand, soda ash and limestone, are melted in a furnace and then flowed on to a bath of molten tin. The glass is formed and gradually cools as it moves from the tin bath to an annealing lehr, which is a controlled cooling chamber. As it moves through this process, the glass is in the form of a continuous ribbon, which is cut to size and packaged at the final stage.

What are the most common types of glass?

All float glass as it is initially made in the above description is called annealed and is the most common. Float glass is made in a variety of colors or tints, in addition to basic clear glass. Annealed glass, the starting point can be further fabricated in many ways. Coatings of various types can be applied to achieve many visual effects and affect the optical properties. In addition the glass can be heat treated to increase its strength and give it safety glazing properties. Glass can be put into an insulating glass unit, meaning two or more pieces of glass are separated by a dry air space to improve the insulating properties.

What is the best glass product for the sunbelt areas of the country?

Proper window design in the south must account for solar heat gain in order to help reduce air-conditioning. Therefore glass products should have a low solar heat gain coefficient or low shading coefficient; the u-value, or insulating performance is of lesser importance.

What is the difference between long wave and short wave infrared?

  • Short wave infrared energy comes directly from the sun but is not felt as heat. It converts into heat when it strikes something.
  • Long wave infrared is the heat radiated from an object which has received short wave radiation, a hot automobile dashboard, for example, or a hot sidewalk or roadway where you can often see heat radiating from the surface.

What are the Shading Coefficient and the Solar Heat Gain Coefficient?

These terms are mathematically related and both describe the solar energy blocked from passing through a glass material. The shading coefficient is the ratio of solar energy that passes through a piece of glass relative to piece of 1/8” clear glass ( which has a shading coefficient of 1.0. Solar heat gain coefficient represents the solar gain through the glass relative to the incident solar radiation; it is equal to 86% of the shading coefficient. In either case, a lower number indicates improved solar control over the 1/8” clear glass baseline.

What is better, a high or low shading coefficient?

In colder, heating-dominated climates such as Canada or northern US, windows with higher shading coefficients generally are preferred and conserve energy. This so because in the longer heating season, more solar radiation, which becomes “free” heat is allowed to pass into a home.

In the south, with a long air-conditioning season, it is most important to reduce solar gain and therefore reduce air conditioning loads.

Does long wave infrared energy only come from the sun?

Any heat source, such as furnace or engine which consumes and combusts fossil fuel, release long wave energy. Any object, like a sidewalk or road or windowsill, which has been exposed to short wave solar radiation will also emit long wave infrared energy.


What is safety glazing?

Glass is a breakable material, which when broken into smaller sharp pieces often called shards can cause serious injury. Safety glazing material, usually tempered glass or laminated glass, reduces the risk of injury. This is accomplished in the case of tempered by the characteristic break pattern-many small pieces, and by the adhesion of the glass pieces to the inner plastic layer in the case of laminated glass.

What is security glazing?

Security glazing products usually involve multiple layers of glass, and in some cases acrylics, usually laminated, in order to achieve maximum impact resistance from explosions, ballistic assaults and even simple forced entry. There is a wide range of such specialty glass products.

What are the U.S. Standards for testing safety glazing materials?

ANSI Z97.1 and CPSC 16CFR, Part 1201.

Where should safety glazing be used?

The Federal safety glazing law stipulates that safety glazing be used in architectural applications ( homes and buildings ) in defined hazardous locations. Generally the hazardous location include doors, immediately adjacent sidelites, bath and shower enclosures and glazing adjacent to passages where there are walking surfaces adjacent to the glass and the bottom edge of the glass is within 18” of the floor. In addition to the Federal law, various local code authoritites have additional requirement.

Are there special safety glazing requirements in overhead glazing?

Many local building codes mandate special considerations for overhead glazing. It is common to require and use tempered glass in residential overhead applications. Laminated, often heat-treated glass is commonly required in commercial building applications. Often, when tempered glass is allowed in commercial building, some form of restraining screening is also required below the glass.

How is safety glazing marked for identification?

The Federal safety glazing law requires that all safety glazing products have a permanently identifiable marking on each piece. This marking cannot be removed without damaging or breaking the glass and is generally located in one of the corners of each piece.


Can you use PPG Low-E glass in a single-glazed window?

Sungate® 500 coated glass can be used single-glazed, provided that the coating is oriented toward the interior of the building. However, PPG does not recommend that the product be used in single glazing applications due to the increased difficulty in routine cleaning. The crystalline nature of the coating can cause dirt and other contaminants to become more difficult to remove, and normal cleaning solutions can leave streaks due to the increased difficulty in removing them before they evaporate.

Sungate® 100 coated glass and Solarban® 60 coated glass must be used only as a component of a sealed insulating glass unit.

In addition, all Low-E coated glasses yield their best energy performing characteristics when used in a sealed insulating glass units.

Is it better to have the coating on the #2 or #3 surface of an insulating glass unit?

The answer to this question is really dependent on the specific design conditions of your application. The light transmittance and U-Value of the unit will be the same whether the coating is on the #2 or #3 surface; however, the Solar Heat Gain Coefficient will be lower when the coating is on the #2 surface.

In general, if you are concerned about reducing solar heat gain (typically in a cooling climate), then using the coating on the #2 surface would best meet the requirement. On the other hand, if you are interested in utilizing passive solar heat gain (typically in a heating climate) then using the coating on the #3 surface would best meet the requirement.

What are the differences between PPG Low-E coated glass products?

PPG manufactures a variety of low-e coated glasses using two different manufacturing processes. The following table identifies the PPG product and associated manufacturing process.

PPG Low-E Coated Glass Products


Manufacturing Process

SUNGATE 500 Coated Glass


SUNGATE 100 Coated Glass


SOLARBAN 60 Coated Glass


In the Pyrolytic manufacturing process, the coating is applied to the glass ribbon while it being produced on the float line and the coating then “fuses” to the hot glass surface. The glass is then cut into stock sheets of various sizes for shipment to fabricators. As a pyrolytic coating, the Sungate 500 coating is very durable, both mechanically and chemically. And, while Sungate 500 coated glass offers reduced emissivity and some solar control, it is not as good a performer as PPG’s MSVD coated glasses.

In the MSVD (Magnetic Sputtering Vapor Deposition) process, the coating is applied to pre-cut glass (usually in stock sheets for further fabrication) in a vacuum chamber at relatively low temperatures. MSVD coatings, such as Sungate 100 and Solarban 60 offer lower emissvity and superior solar control than pyrolytic low-e coatings, such as Sungate 500 glass. However, MSVD coatings are not as durable as pyrolytic coatings, either mechanically or chemically, and must always be used as a component of an insulating glass unit with the coating located within the sealed airspace.

Do all Low-E coated glasses look the same?

No, they do not. Color differences between various low-e coatings are due to the use of different coating materials, the thickness of the various coating layers, as well as differences in manufacturing processes.

Will Low-E glass work only in northern climates?

No, low-e coated glass can work in all climates.

Low-e coatings reduce heat loss from the interior through windows, thus reducing the energy used to heat buildings and associated heating costs.

And, low-e coatings also offer solar control that reduces heat gain due to both the transmitted solar energy and conducted heat caused by indoor – outdoor temperature difference. This reduces cooling loads and consequently the energy and costs associates with cooling the building.

What is required to maintain a PPG Low-E glass product?

Since all PPG MSVD low-e coatings must be sealed within an insulating glass unit, no maintenance is required. If Sungate 500 low-e glass is used in a single glazing application, or as a storm window, then normal cleaning with a mixture of 50% water and 50% isopropyl alcohol is recommended.

Do Sungate Low-E coatings work as well at night (when the sun isn't shining)?

Sungate Low-E coatings work 24 hours a day. In the winter, they reflect the heat (long-wave infrared energy) back into the interior, day and night. Low-E coatings do not differentiate between furnace heat and heat created by solar energy, as they are both absorbed and re-radiated as long-wave infrared energy.

How do SUNGATE and SOLARBAN coated glasses reflect the heat?

First, heat is transferred in three ways: Conduction, convection, and radiation. SUNGATE and SOLARBAN coatings directly affect only the radiated component of the heat transfer. The coatings incorporate an extremely thin metallic layer that reflects the radiated energy (heat), similar to the way a mirror reflects light.

How can PPG Low-E work both in the summer and winter?


  • In the winter, PPG Low-E glass keeps more heat inside by reducing the amount escaping though the glass and therefore reduces heating bills.
  • Some heat (long wave infrared) is not permitted to enter the home, but this is outweighed by the benefits of the amount of extra heat kept inside (much less heat escapes).
  • Some short wave infrared is still allowed to enter the home and is converted into heat.


  • In the summer, PPG Low-E glass reduces the amount of heat that enters through the glass thus reducing the solar heat gain and decreasing cooling costs.

In General

  • It's a matter of where the most heat is coming from, in summer it is outside, and in winter it is inside. PPG keeps the heat where you want it.

How much does PPG Low-E glass reduce the transmission of ultraviolet (UV) energy?

The reduction in the transmittance of UV energy is dependent on the specific PPG low-e coating and the make-up of the insulating glass unit, i.e., glass thickness, glass type, etc. Please refer to the product performance charts elsewhere on the PPG Website for specific information.

Will PPG Low-E glass affect my plants?

First, in addition to the glass and low-e coating, other factors such as the available solar energy and angle of incidence (season of the year, latitude) and specific plant type need to be considered. Also, environmental factors such as temperature, relative humidity, and potential contaminants are important factors. A horticultural specialist is best suited to address specific issues and plants.

However, the following is offered to help with your decision:

The wavelength of radiant energy used during photosynthesis is between 320 and 700 nm.

The maximum % energy transmitted by SOLARBAN 60 coated glass, for example, is between 400 and 700 nm, the same energy range as that primarily used by plants. For comparison, the total visible light (380 to 770 nm) transmitted by a 1” clear insulating glass unit (2 lites of ¼”clear glass with a ½” airspace) is 79% versus 69% for a similar unit with a SOLARBAN 60 coating. While this is a decrease in useful solar energy being transmitted, it is less of a decrease than going from unobstructed outdoor growth to growing behind clear glass, or the reduction that may occur simply by placing plants further from the windows.

In general, most plants that can be grown behind a clear glass window would also be expected to grow behind SOLARBAN 60 coated glass units.

What is the payback on PPG Low-E windows?

The amount of time that it takes to recover the cost of using low-E in windows from heating and cooling fuel bill savings varies. A number of factors affect the period of time:

  • The quality of installation of the window
  • The quality of workmanship of the window
  • How warm or cold the seasons are compared to usual, especially winter
  • Whether windows are kept open in the winter
  • The amount of shading from large trees or from blinds
  • Geographic location
  • One thing that you can count on is that PPG Low-E windows will make the home a more comfortable one.

Does a window with PPG Low-E glass appear any different from a regular window?

There is a slight difference in appearance, but this difference is extremely difficult to see between windows in different parts of a home or building. If you install a lite of low-e glass directly next to a lite of clear glass, you will most likely notice a slight difference. If you install all low-e glass on a particular building, it is a low probability that the typical observer will know that it is any different than clear glass.

Will I notice a difference in the amount of sunlight through my windows if I replace clear glass with Low-E glass?

Initially you may be aware of a slight reduction in the intensity of light coming into your building compared to your old windows. When sunlight is coming directly through windows in which clear glass has been replaced with low-e glass, most people say that the low-e is more comfortable because they feel less heat and glare from the sun. An insulating glass unit with Solarban® 60 solar control low-e glass, transmits about 13% less visible light than an insulating unit with all uncoated clear glass, and about 48% less total solar energy.

What is ultraviolet (UV) light?

The sun’s energy, or solar energy, includes ultraviolet, visible, and infrared energy. Ultraviolet light or UV is short wavelength energy with wavelengths from 290 to 380 nanometers. It is invisible and accounts for approximately 2 percent of the solar energy that reaches the earth. A 1” insulating glass unit with Solarban® 60 solar control low-e glass allows only about 14% of the UV that reaches the earth to pass through the insulating glass unit.

Do blinds, shades, trees, and awnings affect the way that my windows perform?

The answer is yes and no. These items may restrict the amount of heat and light that enters the home through the windows, but they do not change the functional properties of PPG low-e glass.

Should I put PPG Low-E glass in my windows on all exposures and not others?

  • PPG Low-E glass can improve window performance for all exposures all year round.
  • In the winter, PPG Low-E is a benefit because it retains heat no matter which direction the window is facing.
  • Therefore, PPG Low-E is especially useful on north-facing windows in winter because they resist heat loss.
  • PPG Low-E is useful for east, west, and south facing windows because it will reduce solar energy transmission.
  • At the same time, the PPG Low-E is a benefit for these exposures because at night the window is saving money by preventing heat from escaping

Can tinted glass be used with Low-E glass?

Yes it can. Tinted glass can be used as the outdoor lite in an insulating glass unit, with PPG Low-E as the indoor lite. The low-e coated glass improves the insulating properties of the insulating glass unit, while the tinted glass reduces the influx of solar energy through the insulating unit.

How effective is tinted glass with PPG Low-E coatings?

  • Tinted glass is very effective when used in conjunction with PPG Low-E glass. This combination will reduce excess heat gain and lower cooling costs.
  • The tinted glass reduces the amount of excess heat gained on east, west, and south exposures

Is it any harder to clean windows that contain PPG Low-E glass?

No. If your windows have PPG low-e glass, the low-e coating is glazed inside a sealed insulating glass unit. The coating is not exposed to the atmosphere. The indoor and outdoor surfaces of the insulating glass in your windows are plain uncoated glass surfaces, and will clean like normal glass.

How do I know that my window actually has Low-E glass?

Low-e glass is plain sheet of glass that has a coating put onto one of its two surfaces. To improve the insulating properties of windows, that plain sheet of glass is put together with another piece of glass to make a sealed insulating glass unit. The low-e coating goes inside the insulating unit.

You can test for the low-e coating in a window by doing the following:

  • Hold a match or a pen light up in front of the window. You will see four reflections of the flame from the match or the light from the penlight when you look at the glass.
  • If you have low-e, one of the images will be a different color than the rest of the images.
  • If your window has no low-e, the four reflected images will be the same color.

How does argon gas work?

Insulating glass can be made with air between the lites of glass or it can be made with other gases between the lites of glass. Putting argon inside the insulating glass in a window improves the insulating value of the IG unit and the overall window. The bottom line is, less heat flows through a window with argon between the lites of glass than through a window with air between the lites.

Is Argon Gas Dangerous?

Argon gas is an inert gas and it exists in small quantities in the atmosphere around us. We breathe it everyday, and it is harmless. It is not toxic nor is it poisonous to humans. However, you could not breathe only argon. Your body needs other components of the atmosphere to live. Argon gas that is inside insulating glass units is not dangerous.