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- High Intensity Discharge Lighting • A – Natural sunlight is best but artificial lights are needed with short days with low sunlight angle • B – Greenhouse structure, type of glazing materials, overhead equipment and overhead baskets may reduce light • A – plants grow faster • B – flower earlier • C – more compact with more branching • D – thick dark green leaves • E – produces supplemental heat • A – lower irradiance for longer period of time is preferable to higher levels for shorter time • B – 400 to 500 foot candles (4 – 5 klux) for 18 hours for cut flower and potted plants • C – higher then 700 foot candles can cause damage • A – Sunlight contains: • 1 – visible light from 380 to 780 nanometers • 2 – infrared and ultraviolet radiation • B – color • • • • 1 – 400 nm = violet 2 – 500 nm = blue/green 3 – 600 nm = yellow 4 – 700 nm = red • C – maximum photosynthesis occurs at 675 nm • D – chlorophyll reflects yellow - green, and absorbs blue and red • E – red light is necessary for photosynthesis, chlorophyll formation, seed germination, seedling growth, stem elongation, and flowering • F – blue light is necessary for photosynthesis, chlorophyll formation, reduces stem length, increases branching and stem strength • G – light spectrums may be controlled by the glazing materials used • A – lights are most beneficial during early developmental stages • 1 – start from seedlings for 4 to 6 weeks • 2 – not economically significant past 6 weeks • B – for vegetative cuttings use light until flowering • A – Incandescent Lights (not HID) • 1 – lights that contain glowing filament • 2 – convert only 6.5% of energy to light and rest to heat • 3 – light primarily in the far red range • B – Fluorescent Lights (not HID) • 1 – more efficient and much cooler • 2 – very large fixtures which add to shading • 3 – commonly used in growth chambers in combination with incandescent lamps for a better blue to red ratio • C – Metal Halide (MH) • 1 – emit white light similar to sunlight makes them effective in retail areas and interiorscapes • 2 – provide the best spectrum with more reds, far-reds, and blues then HPS • 3 – less efficient and shorter lived then HPS • D – Low Pressure Sodium (LPS) • 1 – most efficient with the highest lumen rating per watt • 2 – undesirable spectrum distribution and high initial cost • E – High Pressure Sodium (HPS) • 1 – emit mostly in the yellow-orange-red range of 550 to 700 nm • 2 – provide the most photosynthetically useful light per watt •3 – smaller fixture causes less shading • 4 – available in 400 W (most common) and 1000 W units • A – Reflectors • 1 – mirror that reflects toward the crop • 2 – provides better light distribution and less fixtures needed • 3 – direct as much as 90% of light to crop • B – Light is only ONE requirement of plant growth; without carbon dioxide, water, fertilizer and temperature, managing light is useless