wouldn't let me edit so I had to delete and repost
Plant Lighting Fundamentals
Understanding PAR
While a plant benefits to a small degree with the light wavelength or spectra that the eye see's, plants respond best to the Ultraviolet (UV) and Infrared (IR) regions of the spectrum. However if the spectrum is narrowly or not at all emitted by the lamp then the plants will not develop to its fullest leafy vegative or bulky flowering stages that natural sunlight would have intended.
Since light plays such a critical role in a plants successful growth it's important to have the proper quality and quantity of light available to the plant as it needs it. Insufficient light levels will reduce a plants overall weight and develop symptoms of stress, decreased nodule density and smaller leaves. While too much light can damage the plant from excessive IR heat radiation or extreme UV radiation.
As it relates to proper light selection we'll introduce you to the importance of two biological reactions that occur within a plant; Photosynthesis and Photomorphogenesis
Plants absorb light by a green pigment within the plant known as chlorophyll. When chlorophyll absorbs light and turns it into energy it is through a chemical process within the plant called Photosynthesis.
As Photosynthesis occurs, the wavelength spectrum that is most beneficial to plant growth is found within certain areas between the 380-720 nanometer range of the spectrum. The light that is within this region is referred to as Photosynthetically Active Radiation (PAR).
A plants spectral lighting needs will change as it grows. Since spectrum plays an important part in the success of the plants growth developmental bioligists refer presence of these light mediated changes that the plant absorbs through a variety of
Receptors as Photomorphogenesis.
As shown within the chart below, you can see the average PAR ranges for most plants that should be available for maximum chlorophyll absorption. Within these ranges plants will respond very well to the emitted light wavelengths.
| Nanometers | PAR Influences |
|---|
| 200 - 280 | UVC ultraviolet range; extremely toxic to plants. |
| 280 - 315 | UVB ultraviolet light; causes plants colors to fade. |
| 315 - 380 | UVA ultraviolet light; is neither harmful nor beneficial to plant growth. |
| 380 - 400 | Start of visible light spectrum. Chlorophyll Absorption begins. UV protected plastics ideally block out any light below this range. |
| 400 - 520 | This range includes violet, blue, and green bands. Peak chlorophyll absorption influences photosynthesis. Most significant in promoting vegetative growth. |
| 520 - 610 | This range includes the green, yellow, and orange bands and has little absorption by receptors. |
| 610 - 720 | This is the Red band where large instances of chlorophyll absorption occur which promote flowering and budding. |
| 720 - 1000 | There is little chlorophyll absorption in this range. Flowering and germination are influenced at the high Far-Red end as infrared heat. |
| 1000+ | Totally infrared range. All energy absorbed at this point is converted to heat. |
Measuring Plant Lighting
We measure visible light in
Lumens, LUX, Lumens Per Watt or Footcandles but are these same measurements also adequate when measuring for a plants lighting levels? No.
While there is nothing wrong with knowing these measurements these are not the best measurements to tell us what is the best lamp for the our plants overall lighting needs.
A better way to measure plant lighting is to determine how much energy the lamp consumes and how much light actually makes it to the plant surfaces where both Photosynthesis and Photomorphogenesis occurs.
When measuring light QUANTITY for a plant we look to measure how many PHOTONS, (the minimum unit of energy involving light) are falling each second within a square meter. Photons are such a small unit of measurement that they are referred to as MICROMOLES OF PHOTONS or more often just MICROMOLES to describe a measurement of how many photons are arriving at a plants surface from the emitted light source. For reference 2000 micromoles would be a sunlight level measurement of light.
Of most value to the grower and his plant would be the number of photons being measured at the plant, per second, per square meter, within the PAR ranges of 380-720 nanometers. This value is then known as the PHOTOSYNTHETIC PHOTON FLUX (PPF) level that the lamp emits.
Meters that measure these (PPF) values are often referred to as QUANTUM METERS since a quantum is the amount of energy carried by a photon. These meters will provide entire spectrum measurements of the total number of photons per second values as well as measure the YIELD PHOTON FLUX (YPF) of the lamp which is as we've seen by the plants photomorphogenis requirements will assist the grower in identifying that the lamp has the proper PAR spectrum for maximum photosynthetic repsonse at that stage of plant growth.
Another way growers like to measure light for plants is by PAR WATTS. What this refers to is how much light energy is available between the 400-700 nanometer ranges that the plant requires for Photosynthesis. What is extremely important to know the efficiency of the lamp being considered. Growers should be careful when considering these values and not to correlate higher PAR WATT values with more successful yields since with energy efficient lighting such as induction the PAR Watts per Square foot may measure 70% less than an HID and while still delivering micromoles in excess of the HID within the plants PPF and YPF requirements. We publish our lamp output values in
Watts/Region which allows the consumer to see how much energy the lamp emits in the three regions of greatest importance to known photosynthetic response.
http://www.life.illinois.edu/govindjee/photosynBook.html
http://www.controlledenvironments.org/Light1994Conf/2_4_King/King text.htm
http://plantphys.info/plant_physiology/phytochrome.shtml
plantphys.info/plant_physiology/phytochrome.shtml
http://www.inda-gro.com/pdf/MeasuringPlantLight.pdf
http://jxb.oxfordjournals.org/content/61/11/3107.full
http://jxb.oxfordjournals.org/content/53/376/1935
http://jxb.oxfordjournals.org/content/59/15/4171.full
http://pcp.oxfordjournals.org/content/50/4/684.full
