Effects of Different Colored Lights on Plant Growth

Background

• Many children experiment with the effects of light on plant growth by covering growing seedlings with different colors of cellophane. This is an ineffective way of measuring the effect of light colors on plants, however, because the cellophane has less of an impact on limiting the which colors from the color spectrum are available to the plants, and instead limits the amount of total light that the plants receive.
  
  NASA, on the other hand, has been experimenting extensively with growing plants with limited color spectrum availability, demonstrating the true impact of light color on plant growth.
  
  

Light Colors

• Under normal growing conditions, with the sun as the primary light source, plants receive a full spectrum of colors, which can be divided into red, orange, yellow, green, blue, indigo and violet.
  
  Fluorescent lights are high in blue light, while incandescent bulbs offer a broader range of light wavelengths with an emphasis on red and orange.
  
  By using light-emitting diodes, or LEDs, growers can pinpoint one light wavelength, such as blue, red and green.
  
  

Effects

• In the NASA experiments, scientists focused on a combination of blue and red LEDs, because those are the light wavelengths most crucial in plant growth.
  
  NASA used a combination of blue and red LEDs to grow lettuce and radishes and the plants grew normally, with one exception. Leaves turned a shade of black, but they tasted normal.
  
  The color difference was due to a lack of green light. Green LEDs can be added to result in normal plant coloration.
  
  

Reasons

• Sunlight contains a full spectrum of light colors, but plants rely particularly on blue and red for their growth and production. The blue wavelength plays a crucial role in photosynthesis and the growth of the plant and the production of leaves. When combined with blue, the red wavelength is important for flower growth.
  
  Plants don't use the green wavelength, but rather they reflect that color, which is why plants appear green. The plants grown without green light grow and taste like normal plants, but if they are grown with green LEDs added, they look like normal plants, too.
  
  

Significance

• Not only is knowledge of plant growth under a variety of conditions intriguing for farmers and home gardeners hoping to grow plants effectively indoors, but it could be an important development for space programs like NASA. Light bulbs like fluorescent and incandescent produce too much heat and require too much energy to be effectively used in space. LEDs, on the other hand, only provide light, making them ideal for growing fresh food in space while using the fewest resources.