Red & Blue Light in Plant Flowering


When growing plants indoors, light color is just as important as light quantity. By understanding the effects of red and blue light, you can help your indoor plants develop strong, healthy structures with spectacular blooms.

Benefits of Blue Light

Blue light promotes stem and foliage growth. A predominantly blue spectrum is good for strengthening seedlings and encouraging compact, leafy development.

Sources of Blue Light

Metal halide bulbs (MH) output predominantly blue light. You can also purchase fluorescent grow lights designed to produce full spectrum light weighted toward the blue end of the spectrum (5000 to 6500k).

Benefits of Red Light

When your plants have matured, it's time for a red shift. Red light triggers plant hormones that increase budding and flowering. Red light also encourages vertical growth.

Sources of Red Light

High pressure sodium bulbs (HPS) produce orange-red light. Fluorescent lights tuned to a color temperature of 2700k to 3000k will also output mostly in the red spectrum.

Why Only Red and Blue

The pigment responsible for absorbing light and fueling photosynthesis, chlorophyll, is visibly green; it reflects green and yellow light rather than absorbing it.


  • Grow Lights Make Your Plants Grow! blog: LED Grow Lights
  • ACF Greenhouses website: Indoor Plant Grow Light Guide

Who Can Help

  • Grow Lights Make Your Plants Grow! blog: Hydroponics Lighting
  • Home Harvest Garden Supply website: Buying The Right Indoor Plant Grow Light
  • The Orchid House website: Indoor Plant Lighting
Keywords: color spectrum, indoor grow lights, red light, blue light, flowering plants

About this Author

Nicole LeBoeuf-Little is a freelancer from New Orleans, writing professionally since 1994. Recent short stories appear on and in Ellen Datlow's forthcoming "Blood and Other Cravings." She's published articles in "Pangaia Magazine" and eGuides at She holds a Bachelor of Arts in English from University of Washington and attended the professional SF/F workshop Viable Paradise.

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