There are several different types of double glazed replacement windows.

Double-glazed Clear:

Double-glazed clear glass windows have inner and outer layers of clear glass that are separated with an air gap. Double-glazing reduces the amount of heat loss to half. This is because the air space between the layers of glass acts as an insulator. Also, the, double-glazed windows with clear glass, permits the maximum amount of visible light into a room as well as high solar heat gain.

Double-glazed with Bronze/Gray Tint:
This is double-glazed window with the outer glass layer tinted with either bronze or gray tinting, while the inner glass layer remains clear. Just as with the double-glazed clear glass windows, double-glazed bronze or gray tinted windows have two layers of glass separated with an air gap. Double-glazing reduces heat loss because air space between the layers glass acts as insulation. There is no difference in energy performance between the bronze and gray tinting on the glass products. The tinting
is for solar heat gain reduction, but it also reduces the amount of visible light permitted into the room. Glass tinting helps to cut glare, but you may also be cutting the solar heat gain as well as the amount of visible light permitted into the room. Tinting does not affect the U-factor, however it will reduce the solar heat gain. This is a benefit in the summer and in areas that have mild winters, such as in the southern most states, however this could be a problem in very cold climates.

Double-glazed with High Performance Tint:
If you could take the best of tinted glass and clear glass then merge them together you would come up with high performance tint. This glass tinting cuts solar heat gain below that of bronze or gray tinted windows, however, it permits visible light to enter the room almost at the level of that of clear glass. High-performance or spectrally selective tinted glass windows have a pale green or light blue coloration. Tinting does not affect the U-factor, however it will reduce the solar heat gain. This is a benefit in the summer and in areas that have mild winters, such as in
the southern most states, however this could be a problem in very cold climates.

Double-glazed with High-Solar-Gain Low-E, Argon Gas:
Low-E glass reduces the amount of heat loss at the same time permitting solar gain. High solar gain Low-E glass windows work best in homes and buildings in heating-dominated climates. Windows that have a high solar gain glazing work best in winter, or cold climates while low solar gain windows do best in the summer and warmer climates.

Double-glazed windows with Moderate-Solar-Gain Low-E, Argon Gas:
These windows cut heat loss at the same time permit a sufficient quantity of solar gain. Double-glazed windows with moderate-solar-gain Low-E, Argon gas are fantastic for climates with heating and cooing concerns.

Double-glazed with Low-Solar-Gain, Low-E, Argon Gas:
Low-E windows occasionally referred to as spectrally selective Low-E glass, reduce the amount of heat loss in the wintertime, as well as cut the heat gain during the summer. When compared to most tinting and reflective glazings, double-glazed with low-solar-gain, Low-E, argon gas windows present a greater level of visible light permitted into a room for a given amount of solar heat reduction. These windows are perfect for homes and buildings in cool-dominated climates.

Variations on low solar gain Low-E coatings have been used to reduce the solar gains even moor. These variations however, also reduce the amount of visible light permitted into the rooms. These coatings slightly tint the windows and are for use in climates where cooling is the leading aspect and where a tinting is desired, for instance in such area as sunrooms, or beach home.