Light is the most essential factor for plant growth. The growth of plants and the length of time they remain active depends on the amount of light they receive, and that is determined by the three aspects: (1) Intensity, (2) Duration and (3) Quality.

Light intensity influences the manufacture of plant food, stem length, leaf color, and flowering. House plants can be classified according to their light needs, such as high, medium and low light requirements. And it depends upon nearness of the light source to the plant (direction of window in house and exposure of plant to natural sunlight).

However, plants require some period of darkness to develop properly and thus should be illuminated for no more than 16 hours. Excessive light is as harmful as too little light.

For artificial lights used as the only source of light for growing plants, the quality of light (wavelength) must be considered. For photosynthesis, plants require mostly blues and reds but for flowering, infrared light is also needed.

  • Incandescent lights produce mostly red, and some infrared light, but are very low in blues.
  • Cool white florescent lights produce mostly blue light and are low in red light.

Blooming plants require extra infrared which can be supplied by incandescent lights, or special horticultural type fluorescent lights.

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