What Light Rays Make Plants Grow?


The energy plants need to grow is produced by photosynthesis, the process for converting light into food and oxygen. Plant proteins called phytochromes sense different light colors. Sunlight has the full spectrum of light; man-made lighting can supplement indoor lighting.

Red Light

Red rays cause plants to release hormones for flowering and budding, and start germination. Although red rays promote plant growth, too much can make a plant thin and spindly. High-pressure sodium lights give a red glow for plants in limited sunlight.

Blue Light

Openings on leaves, called stomata, determine a plant's water detention. Blue light rays determine the size of the stomata-the larger the stomata opening, the more moisture lost. Full-spectrum LED and metal halide lights emit blue rays for growing plants without sunlight.

Green Light

Plants absorb and use every color in the light spectrum except green. Instead, plants reflect back the color green, which is why plants appear green to humans.

Cool White Light

Foliage plants such as ferns grow well in the cool white light rays of fluorescent lights. This type of light is most office buildings. Many plants that do well in cool white light need up to 18 hours of light per day. Light sources should be left on or regulated by timers.


Full-spectrum “horticultural” fluorescents provide rays from the entire light spectrum. It's the closest alternative to natural sunlight and is good for most plant types. Plants under full-spectrum horticultural fluorescents can thrive with no other light source.


  • Garden Guides.com: How Different Lights Make Plants Grow
  • Gardening Know How.com: How Light Affects the Growth of a Plant
Keywords: Light and plants, Plants and light, Rays and plants

About this Author

Kim Schumer worked as copy editor, features writer, editor and freelance writer for Gannett and MediaNews newspapers beginning in 1993. She won numerous industry awards through the years, and she still freelances for Gannett. She studied creative writing and history at Southwest Missouri State University.

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