Length of Exposure

• Plants obtain food via photosynthesis and the more sunlight a plant receives the more nourishment it obtains. According Colorado State University Extension, most plants respond well to at least 12 to 14 hours of sunlight, but do not do well if light exposure occurs 24 hours a day. Some plants such as poinsettias and Christmas cacti do better when exposed to longer periods of darkness, while others, such as onions, experience better growth when exposed to lengthy periods of light.
  
  

Quality of Light

• Light quality is important to plant growth. According to Oregon State University Extension, light quality is defined by the wavelength or color of the light. When a plant is exposed to outdoor sunlight, the light prisms spread light color in an optimal way, providing everything a plant needs. Light quality for indoor plants needs to be manipulated. When growing seeds, cool, florescent light works best because they are in the blue range. Broad spectrum florescent lights are more red and work best for grown and flowering plants.
  
  

Intensity of Light

• The intensity of light a plant is exposed to can affect growth. House plants require low light and can thrive when exposed to light through a sunny window. The intensity of light needed by outdoor plants varies. Most plants grow best in areas where there is morning sun and afternoon shade. Plants growing in afternoon sun and morning shade, full sun for eight hours or more, or full sun with reflective heat, may become too hot for adequate growth. Only shade-tolerant plants do well in filtered shade, open shade or closed shade.