Does a Plant Grow Faster Under a Red Light or a Green Light?

Different light colors affect how fast a plant grows.

The color of the light a plant is exposed to affects how fast it grows. Red and blue lights affect plant growth the most. Green light has the least effect on how fast a plant grows.

Sunlight

Sunlight contains the full spectrum of light colors and plants use all of these colors for photosynthesis. However, some colors are more important than others are, when it comes to plant growth. The two most important colors are red and blue.

Colors

Blue light encourages the growth of leaves. Red light stimulates the growth of flowers, but too much red light makes plants spindly. Plants are green because they reflect green light waves, instead of absorbing them. Therefore, green light has the least effect on them.

Bulbs

Cool white fluorescent lamps have a lot of blue light and are good for starting seeds, but plants grown under them may be somewhat stunted. If you want to grow flowers, use broad-spectrum fluorescent bulbs, because they emit a lot of orange and red light. Incandescent lights contain a lot of red light but they produce too much heat to be useful in growing plants. Fluorescent "grow" lights try to imitate sunlight but, according to the Arizona Master Gardener Manual, aren't any better than regular fluorescent lights.

References

• Colorado State University Extension; Plant Growth Factors -- Light; David Whiting; December 2009
• Arizona Master Gardener Manual: Environmental Factors That Affect Plant Growth
• Garden Simply: Growing Under Lights

Resources

• University of Hawaii: Growing Plants Indoors Under Supplemental Lighting; Kent Kobayashi