Formula

• Drop a stone in a pond of still water, and a ripple pattern is set up. Light is like that. It has crests and troughs. Measuring from the top of one crest to the top of the next gives its wavelength.
  
  

Colors

• Light spans from short to long according to ROYGBIV: red, orange, yellow, green, blue, indigo, and violet. Red light is long and violet light is short. Beyond violet is a form of light that is invisible to human eyes. It is ultraviolet.
  
  

Energy of Light

• The higher the frequency or shorter the length, the higher is the energy of light. Ultraviolet has much more energy than red light. To increase growth, plant lights favor the violet end of the spectrum.
  
  

Other Factors

• Increased energy is not the total solution. Plants are green. Chlorophyll in plant leaves does not absorb green. Green is "spit out." Other leaf substances do not absorb certain frequencies well, either.
  
  

Red Portion

• Seeds sprout and grow well under higher-energy light, but flower production improves when light from the red part of the spectrum is included.