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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
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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