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Understanding light, what it is, and how it works, is essential to gardeners because light provides the energy which stimulates plant growth. Although we tend to take it for granted, light is a building block of life on Earth. Plants rely on light to produce food and maintain healthy growth and flowering. In order to use light effectively, you need to know how to measure it and how and when to employ the use of artificial light.


Light and Plant Processes 245770d1219260678needed

What humans see as colors*, plants see as stimulants to food production, flowering, dormancy, seed germination, chlorophyll manufacturing, branching, and leaf thickening. In addition, plants also respond to a wider spectrum of light than do humans. Plants utilize radiant energy from 280-800 nano-meters,** while humans can detect only from 380-760 nm. Although plants utilize a wider spectrum, they do so selectively.

Although light is a crucial element in many plant processes, not all frequencies of light affect plants equally. For instance, photosynthesis is stimulated by both red and blue light, while photoperiodism is governed by only red and far-red wavelengths and phototropism utilizes the blue and blue-green spectrum. Each plant variety may respond a little differently to each color of the light spectrum. For this reason, a little experimentation may be necessary to find the specific light spectrum your plants desire. Most gardeners have found that a well-balanced mix of red and blue hues is good for all over coverage, while others go a bit more specific and alternate between colors or use one exclusively.

*Plants and humans use different parts of light. Plants use photons which carry energy, while humans use waves to see their environment in color. People use photons directly also. Light photons striking our skin (sunlight and tanning lights) produce vitamin A, D, & E, all vital to our health.

**One nano-meter (nm)  + one billionth of a meter


Light Intensity

Plants discriminate not only by light color, but also by light intensity. Intensity measures quantity of light energy per unit of time. Light intensity requirements vary with each plant species. With an understanding of light intensity, it is possible to employ artificial lights successfully. In fact, you can control light so successfully that it is possible to grow robust plants even in the complete absence of natural sunlight! The first and foremost quality of artificial light is that it fades fast. Very fast. To overcome fast fading you can:

  1. Choose a bright light
  2. Choose an efficient reflective hood with even light distribution
  3. Maintain short plants (2-3 feet in height) with widened branches so light penetrates the foliage

When choosing a lighting system for your indoor garden, pay attention to how much light is being emitted by the lighting system and how much is actually received by the plants. Plants grown on the outside of a lighted area receive less intense light than those grown directly below the source. When establishing a grow room, always be sure to give each plant the minimal daily light requirement necessary for full growth; sometimes this means moving pots around, tying down branches, or even pruning excess foliage.




1. “GARDENING INDOORS with H.I.D. LIGHTS” written by George F. Van Patten and Alyssa F. Bust

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