Color

• Blue light is critical for promoting vegetative growth in plants. According to Botany Basics, a website produced by the Oregon State University Extension Service, certain wavelengths of red light are known to encourage budding or flowering in plants. Plants appear green because they do not absorb green light; they reflect it.
  
  

Wavelength

• Even more important than the color of a light source is the wavelength of that color. Plants mostly absorb blue light from wavelengths between 400 and 480 nanometers as well as red light from wavelengths between 610 and 690 nanometers. A nanometer is defined as one-billionth of a meter.
  
  

Intensity

• The intensity of light at a particular wavelength is also important in determining the overall effectiveness of a blue or red light. Flowering plants will respond better to more intense light sources.
  
  

Lighting

• There are several types of lightbulbs on the market that are ideal for plant lighting. High-pressure sodium lamps emit certain amounts of light in the red spectrum. Red LED lights are available in very specific wavelengths which can make them ideal for flowering.
  
  

Facts

• Cool white and blue light work well to encourage growth in seedlings. Generally, full-spectrum lightbulbs are not good sources of lighting for flowering plants because so much of the light put out by the bulb is not absorbed by the plant.