When placing houseplants near a window, a tint or film complicates whether the plants will receive enough energy to thrive. Tinted windows reduce the amount of light entering a room, creating a different environment than clear glass. The success of a plant depends entirely on the tint’s darkness and the specific light needs of the chosen plant species.
The Physics of Tinting and Photosynthesis
Tinted windows are engineered to filter the sun’s energy, directly impacting plant life. Photosynthesis, the process plants use to create food, relies on Photosynthetically Active Radiation (PAR). This range includes wavelengths from 400 to 700 nanometers, with plants primarily using blue light (for vegetative growth) and red light (for flowering).
Tinting dramatically reduces ultraviolet (UV) light transmission, often blocking up to 99%. This is beneficial since UV rays are not used for photosynthesis and can cause cellular damage or leaf burn. However, the tint also reduces the overall amount of visible light, measured by its Visible Light Transmission (VLT) percentage. A film with a 50% VLT, for example, allows only half of the visible light to pass through.
The light reduction is a simple dimming effect across the entire visible spectrum. It is not a selective blocking of the red and blue wavelengths plants need. While a tinted window may appear bright enough to the human eye, the total energy available to the plant for growth is significantly lower. The perceived brightness is not a reliable indicator of the usable PAR for a plant.
Quantifying Light Reduction and Minimum Thresholds
Light intensity is often measured in foot-candles (FC), which quantifies the light falling on a surface. Understanding these measurements helps relate the window’s VLT to the plant’s biological needs. The minimum light requirement for a plant to survive is called the light compensation point. Indoor plant requirements are typically grouped into three categories.
Low-light tolerant plants need a minimum of 25 to 75 FC just to survive, thriving in the 75 to 200 FC range. Medium-light plants require a higher baseline, needing 75 to 150 FC minimum, and prefer 200 to 500 FC for healthy growth. For reference, a bright, unshaded south-facing window provides thousands of FC, while a spot 10 feet away might drop to 100 FC.
The effect of a tinted window is a direct percentage reduction of the light reaching the plant. For instance, a 50% VLT window cuts the incoming light in half, potentially dropping a location from a medium-light environment (500 FC) to a low-light environment (250 FC). If the VLT is too low, perhaps below 25%, the light may not be sufficient for any but the most shade-tolerant species. To accurately determine the light level after tinting, use a simple light meter or a smartphone app to read foot-candle levels at the plant’s canopy.
Choosing Plants for Reduced Light Conditions
The most successful plants near tinted windows are species adapted to the low-light conditions of the forest floor. These plants have a biological tolerance for reduced light due to their lower light compensation point, needing less energy to maintain basic life functions. Their metabolism is often slower, resulting in a reduced growth rate compared to sun-loving plants.
Excellent choices for these environments include the ZZ Plant (Zamioculcas zamiifolia), known for its waxy, dark green foliage efficient at light capture. The Snake Plant (Sansevieria trifasciata) and the Cast Iron Plant (Aspidistra elatior) are resilient, maintaining health where other plants would decline. Pothos (Epipremnum aureum) and the Peace Lily (Spathiphyllum) also tolerate low light, though their growth will be slower and variegation less pronounced.
To maximize the available light through a tinted window, plants should be placed as close to the glass as possible. Even with a tint, the light intensity drops off rapidly as the distance from the window increases. Choosing plants with solid green leaves over variegated varieties is advisable, as the green chlorophyll allows for more efficient use of the limited light.