Supplemental Lighting

Providing supplemental lighting for plant growth can decrease growing times and reduce the risk associated with low sunlight level. Plant growth is directly related to the amount of light energy received on the leaf surfaces. Plants have a saturation level for the amount of light energy they can absorb; above this level, additional light energy will not increase plant growth. The saturation level does vary with plant species. Some of the typical applications of lamps and fixtures in a greenhouse are as follows:

  • Fluorescent fixtures are often used in growth chambers because they are a linear light source rather than a point source so light distribution is more uniform.
  • While “cool white” lamps will encourage good plant growth, special grow lights will enhance plant appearance because of the broader spectrum of light.
  • High intensity discharge (HID) lighting is common for general greenhouse lighting. Both metal halide (MH) and high pressure sodium (HPS) lamps are suitable for greenhouses. A combination of MH and HPS lamps in a one to one ratio is common with the MH contributing light in the blue-violet range and the HPS contributing light in the yellow-orange part of the light spectrum.
  • LED lamps have been introduced by several manufacturers and are being researched. They offer the ability to change the light spectrum to match the plants needs and are more energy efficient but expensive. For the latest recommendations for LED lamps refer to the Michigan State University website – Greenhouse Energy Conservation Strategies: Lighting – www.flor.hrt.msu.edu/energy-lighting/

References:

Evaluating Supplemental Light for Your Greenhouse, P. Fisher, C. Donnelly & J. Faust, University of Hew Hampshire Cooperative Extension, May 2001. Click Here for article

Daily Light Integral (DLI) Calculator, Helps to calculate the amount of supplemental light from a supplemental light source and hours of operation of lights to achieve a target supplemental DLI, University of New Hampshire, Accessible at: http://extension.unh.edu/Agric/AGGHFL/dlicalc/index.cfm

If you have questions about the information on this site, please contact
Scott Sanford, Distinguished Outreach Specialist, University of Wisconsin, sasanford@wisc.edu.