- 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