The Effect of Light on Plant Growth


Anyone who has tried to keep a garden plant on a sunny window sill knows that winter's low light is just enough to sustain it until spring. Light has a major effect on a plant's ability to live and grow.

Plants need light to produce food.

The Nature of Light

Light is energy that travels in waves of differing frequencies. We perceive each frequency as a color. Plants use (absorb) certain frequencies of light and pass (reflect) others along.


Seeds contain embryonic plants with proteins that activate when they receive warmth and light. Although germination requirements vary, the light from the red end of the spectrum that helps trigger germination is found in open (non-shaded) areas in early spring.


Seedlings grow upward toward light, spouting leaves as they break the surface. These leaves begin absorbing light and creating chloroplasts, cells that contain chlorophyll, the pigment that absorbs sunlight.


The addition of water and carbon dioxide in the chloroplast begins a chemical reaction that produces carbohydrates (sugars), enzymes and phosphates. These provide the food the plant needs for growth.


Plants grown in low light (like the winter window sill), stretch toward the light and become pale due to undifferentiated (overworked) chloroplasts. Photomorphogenesis uses light to develop robust chloroplasts, sturdy stems and fully-developed leaves.

Ultraviolet Light

Research at Washington State University suggests that, although visible light provides plant growth energy, ultraviolet light may help plants defend against pests and disease.


  • Photomorphogenesis
  • Light and temperature effects on germination
  • Ultraviolet Light

Who Can Help

  • Photosynthesis
  • Seed Germination
Keywords: garden, plant, light, grow, spring

About this Author

Laura Reynolds began writing professionally in 1974. She has worked as author and editor in nonfiction, professional journals and newspapers. Reynolds has also served in numerous appointed and elected local offices. She holds a Bachelor of Science in education from Northern Illinois University.