Low-E glass is short for low-emissivity glass. It is more energy-efficient than regular glass. To make low-E glass, regular glass is coated with an ultra-thin layer of metal oxide (either tin or silver). This treatment allows virtually all the visible spectrum of light to come through the window but blocks some of the ultraviolet (UV) and infrared (IR) light. UV light can cause fading damage to furniture and carpets, as well as contribute to sunburn. IR light causes heat buildup. Because the visible spectrum of light is most important to plants, you should see little effect on the growth of your houseplants. In fact, they may grow better because the temperature may be more moderate.