Chapter 6

Light and Lighting Control in Greenhouses

(draft 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 areas to consider: quality, intensity, daily duration, and daily light integral. Light quality describes the wavelengths (colors) of light. Intensity is important because rate of photosynthesis and growth increase up to an optimum intensity level and then decrease at higher levels. Light duration is important because the ratio of light to darkness each day controls processes such as flowering and form of growth in many plants. Daily light integral (DLI) is the amount of photosynthetically active radiation (PAR) received each day as a function of light intensity and duration (day). 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
  • Understanding Light Units
  • Estimating Photosynthetically Available Light
  • Effects of Light Intensity on Plant Growth
  • Light Requirements for Plants
  • Maximizing Light Intensity
  • Greenhouse Design
  • Covering Material
  • Plant Spacing
  • Reducing Light Intensity
  • Light Duration
  • Variation in Photoperiod
  • Photoperiodic Plant Response Types
  • Decreasing Day Length
  • Extending Day Length
  • Day-extension
  • Night-extension
  • Cyclical Lighting
  • Photoperiodic vs. Photosynthetic Lighting
  • Lamp Types/Light Sources
  • Incandescent (INC) Light Bulbs
  • High-intensity Discharge (HID) Lamps
  • Compact Fluorescent (CFL) Lights
  • Light-emitting Diodes (LEDs)
  • Daily Light Integral
  • Measuring Daily Light Integral
  • Foot-candle Meter
  • Quantum Sensor
  • DLI Maps
  • Supplemental Lighting
  • Supplemental Greenhouse Lighting
  • Lamp Technology Options for Greenhouses
  • Incandescent Bulbs
  • Halogen Incandescent Bulbs
  • Fluorescent Lamps
  • Compact Fluorescent Lamps (CFLs)
  • High-intensity Discharge (HID) Lamps
  • Light-Emitting Diodes (LEDs)
  • Controlling Greenhouse Lighting Systems
  • Determining Greenhouse Lighting Requirements
  • Carbon Dioxide and Supplemental Light
  • References