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Part1Lecture9-12 - Lighting and Light Control(Meeting 9 and...

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Fall 2002 Biernbaum, MSU HRT 221, pg 19 Lighting and Light Control (Meeting 9 and 10) Ref: Nelson Chapter 10 Why is light critical? By definition, the purpose of the greenhouse is to admit natural light for plant growth. Growth is primarily a function of the chemical reactions of photosynthesis, which utilize light energy to fix carbon dioxide. When characterizing a plant response to light, it is important to remember that plant growth is influenced by three different measure or properties: Intensity: How much light at one moment in time? most common unit of measure is the footcandle full summer sunlight is about 10,000 footcandles light level in this room is 75 to 100 footcandles some plants (poinsettias) are sensitive to as low as 1 to 2 footcandles when estimating plant response we should consider the average light level of the whole plant canopy Duration: How long is the light period? some unit of time, usually hours or minutes very important for determining the total amount of light received: intensity x duration also important for determining photoperiodic responses Quantity of light is a function of Intensity and Duration footcandles x hours = foot candle hours Daily Light Integral (DLI) gives a sum of the total light for the day mmoles per meter squared and second x seconds = moles/day Can range from as low as 2-4 moles/day to 20 to 40 moles/day DLI is one of the best predictors of how much a plant will grow. Quality: What type of light? light quality is defined by the wavelength of light the most common unit of measure is the nanometer visible light is in the range of 400 to 700 nanometer and is composed of violet, blue, green, yellow, orange, and red light photosynthesis is a response to light in the visible range, but photosynthesis is not sensitive to the same wavelengths as the human eye a spectral energy distribution (SED) is a characterization of the wavelength emitted from a source or use in a reaction
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Fall 2002 Biernbaum, MSU HRT 221, pg 20 Maximizing Solar Radiation: - proper orientation - glazing or covering selection - minimizing the superstructure glass : 8 to 10 % reduction frame : 10 to 12 % reduction sash : 5 to 7 % reduction heat equipment, electrical, etc : ? % light levels of 65 to 70 % at the bench not uncommon - superstructure painted - covering kept clean - adequate plant spacing on the bench
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