During summer heat-gain into homes is a big issue, especially when air-conditioning is used to regulate the temperature. It's far more efficient to prevent heat ingress than trying to pump it out afterwards!
Windows, of course, exhibit the "greenhouse effect" whereby light passing through the glass is converted to heat inside the structure. Heat, being long-wavelength, cannot pass through the glass as did the light and is so trapped - the greenhouse.
West and east-facing windows can be a boon in cold weather, allowing direct solar gain during morning and afternoon which can be a welcome brightener during gloomy winter weather. However these windows are prime culprits in admitting unwanted energy during hot weather.
Westerly windows are more noticeable as they admit sun during the afternoon when the house is already warm, the additional heat increasing internal temperatures to uncomfortable levels. However reducing heat gain from eastern windows is just as significant, helping to keep interiors cooler for longer.
Depending on site and geographical specifics, deciduous trees shading windows on east and west sides are very effective, also because they allow sunlight in during winter when the foliage has dropped.
Another option is external blinds which, with opacity of 80-90%, reduce heat load while still allowing some light through the windows. The impinging light heats up the blind but, being external, the energy dissipates without affecting the house.
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