Chapter 7

Light and Lighting Control in Greenhouses

(book excerpts)

Light is an essential factor in growing plants in greenhouses. The rate of growth and length of time a plant remains active is dependent on the amount of light it receives. Light energy is used in photosynthesis, the plant’s most basic metabolic process. When determining the effect of light on plant growth there are three different aspects of light that should be considered: quality, intensity, and length of the day (photoperiod). All three of these characteristics of light affect growth and development of food crops, though in different ways and in varying magnitudes. Light quality describes the wavelengths (colors) of light. Red and blue have the greatest impact on plant growth. Green light is least effective (the reflection of green light gives the green color to plants). Blue light is primarily responsible for vegetative leaf growth. Red light, when combined with blue light, encourages flowering. Light intensity is the total amount of light supplied to the plant, which is then used for photosynthesis; up to a point the higher light quantity the more energy a plant can sequester in photosynthesis. Light duration (i.e, photoperiod) is important because the ratio of light to darkness each day controls processes such as flowering and form of growth in many plants. In commercial greenhouses, several strategies can be used to help properly manage light levels throughout the day and seasonally. Some of the primary reasons why greenhouses manipulate light levels include temperature and irrigation management, photoperiod control, minimizing crop stress, and optimizing photosynthesis. Some of the lighting technologies include, incandescent bulbs, halogen incandescent bulbs, fluorescent lamps, compact fluorescent lamps, high-intensity discharge lamps, and light-emitting diodes.

Click on the following topics for more information on light and lighting control in greenhouses.

Topics Within This Chapter:

  • Light Quality
  • Blue Light
  • Red Light
  • Far-Red Light
  • Green and Yellow Light
  • Distribution of Light from Common Light Sources
  • Full-Spectrum versus Partial-Spectrum Lighting
  • Light Intensity
  • Foot Candle and Lux Light Measurements
  • Quantum Light Measurements
  • Effects of Light Intensity on Plant Growth
  • Light Requirements for Plants
  • Length of the Day (Photoperiod)
  • Plant Response to Photoperiod
  • Creating Artificial Short Days
  • Operation of Black-Cloth Curtains
  • Blackout Materials
  • Greenhouse Temperture Regulation
  • Creating Artificial Long Days
  • Day-Extension
  • Night-Interruption
  • Cyclical Lighting
  • Lighting Options for Controlling Photoperiod
  • Incandescent Light Bulbs
  • Compact Fluorescent Lights
  • High-Intensity Discharge Lamps
  • Light-Emitting Diodes
  • Supplemental versus Photoperiodic Lighting
  • Carbon Dioxide and Supplemental Light
  • Daily Light Integral
  • Daily Light Integral Requirements for Greenhouse Crops
  • The Effects of Low Daily Light Integral on Plants
  • Daily Light Integral and Greenhouse Temperature
  • Determing Daily Light Integral in a Greenhouse
  • Quantum Sensors
  • Foot Candle Meters
  • DLI Maps
  • Supplemental Greenhouse Lighting
  • Benefits of Supplmental Lighting
  • Lamp Types for Greenhouses
  • Incandescent Bulbs
  • Halogen Incandescent Bulbs
  • Fluorescent Lamps
  • Compact Fluorescent Lamps
  • High-Intensity Discharge Lamps
  • Light-Emitting Diodes (LEDs)
  • Controlling Greenhouse Lightings
  • Determining Greenhouse Lighting Requirements
  • Calculating the Number of Lamps for Supplementing Lighting