But, on a Pacific Northwest winter day, light levels may be only 30 percent of what they are on a sunny summer day. When thinking about light levels for houseplants, consider light intensity, duration and quality, recommends Ross Penhallegon, horticulturist with the Oregon State University Extension Service. For instance, a geranium grown in low light tends to be spindly with light green leaves. A similar plant grown in bright light would tend to be shorter, better branched and have longer, darker green leaves. The distance the plant is from the light source and the direction the windows in a home face determine the light intensity a houseplant receives.
Southern exposures have the most intense light.
Western and eastern exposures receive about 60 percent of the intensity of southern exposures. Northern exposures get only 20 percent of the light of southern exposures. Other factors influencing light intensity besides season include the presence and type of curtains, the weather, shade from buildings or vegetation, the cleanliness of the window and the reflectiveness of the surroundings. Houseplant owners can compensate for low light intensity by increasing the time a plant is exposed to light. Increased hours of lighting allow the plant to make sufficient food to survive and grow.