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.