Jeober:
There are many types of coatings some of which work like you described, while others work the entire season to block heat travel (either direction).
Window Radiation Transfer
Clear glass vs. High-transmission low-e vs. Spectrally selective low-e
UNTREATED:
1 Most solar heat enters window
2 Most long-wave radiation is transmitted out window
HIGH TRANSMISSION:
3 Most solar heat enters window
4 Most long-wave radiation is reflected back by low-e coating, reducing winter heat loss
SPECTRALLY SELECTIVE:
5 Most solar heat is reflected by spectrally selective coating, reducing summer heat gain
6 Most long-wave radiation is reflected back by low-e coating, reducing winter heat loss
The graphic didn't paste well, but you can search on the internet for more information...
The stuff at Real Goods may only stop heat gain (not heat loss) but you can check it out at
http://www.realgoods.com/shop/shop2....&kw=window