- Natural light is best for plants during all growth phases, but if you're growing indoors, you must provide the light. It's a good idea to have a basic understanding of the light spectrum and how it affects plant growth, in order to choose the best lighting for your indoor gardening needs.
- Plants manufacture their own food using a process of photosynthesis. Chlorophyll in the plant converts carbon dioxide into food using light energy. Three principles of light affect plant growth: quality, quantity and duration. Quantity refers to light's intensity, while duration is the length of time the light is present. Quality of light refers to its wavelength, or color.
- Sunlight includes all wavelengths, and therefore all colors of light. Plants only absorb light in the red and blue wavelengths, so orange, yellow, green, indigo and violet are theoretically unnecessary. The reason we see plants as green is because they reflect, rather than absorb, green light.
- Blue light helps leaf growth. Cool white fluorescent lights emit light high in the blue wavelength, so they are excellent at promoting a plant's leafing out. The blue light is also useful for starting seedling growth. Combining red and blue light encourages flowering.
- Research by NASA suggests that plants can achieve optimal growth when exposed to only red (about 15 percent) and blue (about 85 percent) spectrum LED (light emitting diode) lights.
- LED lights are available in a variety of colors, use little energy and produce very little heat. They are useful for almost all indoor growing. Fluorescent lights are best for starting seeds and early in the plant's growth cycle. HPS (high-pressure sodium) lights help a plant flower and produce fruit. Metal halide lights emit intense light in the blue spectrum and are ideal for growing lettuce and other leafy green vegetables. Incandescent lights emit light in the red/orange spectrums, but also produce a lot of heat, which may harm plants, so they are not a very good choice to use when growing plants indoors.
