People install windows primarily for daylight and views. Windows allow natural light to flood into the spaces creating an airy and spaciuos feeling. Studies have shown that increased daylighting improves worker productivity, patient health and well-being.
The potential for daylighting buildings is directly related to the amount of fenestration area installed on the building envelope. It is also related to the amount of light allowed through those systems into the building. The ability of a fenestration product to transmit daylight is called Visible Transmittance. People install windows primarily for daylight and views, so the higher the percentage of visible light transmitted, the better.
Spectrally Selective Window Glazing
Houses with large amounts of sun exposure, will benefit from extra high efficiency forms of Low-E insulated glass that actually blocks damaging light from the sun, reducing solar gain through the windows, while maintaining high levels of visible light tramsmittance. Low-E glass is a technologically advanced, insulating glass that improves energy efficiency by reducing the transfer of heat or cold through windows, thus reducing heat loss but allowing the room to be warmed by direct sunshine. Daylighting can save anywhere between 30 to 60% in building energy usage when intergrated with appropiate lighting controls.
The way a window faces has a big impact on its contribution to comfort, heating and cooling loads and daylighting. Windows facing east and west get loe-angled sunlight in the mornings and afternoons, causing glare and overheating the house in summer. Windows facing south can get low-angle sun in spring, fall and winter, particularly the farther north you live. Shading of glass with overhanges, planting or shades will reduce glare, fading of furniture and localized overheating in rooms with south or west facing glass.