Imagine your Dad's oversized variable tint sunglasses and you'll get the idea. But Sage Electrochromics has taken this technology out of the lens frame and into the window frame.

I caught up with Bob Hayes of Sage Electrochromics who gave me a quick demo of the technology which is sweeping the green building industry.

Sage makes windows for both commercial and residential applications and they have storefront and insulated glass units. An electric current is triggered by a switch (that can be put on a timer) which controls the shading.

In addition to helping reduce glare during the sunny part of the day, the Sage windows take a huge dent out of a building's energy bill. A recent study at Lawrence Berkeley Labs indicates that electrochromic glazing can save as much as 40 percent on a building's total energy use.

When the afternoon sun shines through the windows, it adds a great deal of heat, making the air conditioning system work overtime to keep the interior temperature comfortable.

Tinting the windows during those hours cuts the heat gain off at the source, something that interior sun shades cannot do. This green building strategy, while costly up front, is partially paid back off the bat by a reduction in the overall size of the air conditioning system.

And in just a few years, the energy savings will pay for the units ... an example of how the cheapest energy is the energy you don't use. 

Auto-tinting windows can save 40% on energy costs
Sage's electrochromic glass tints during the hottest part of the day, reducing total energy loads.