Cannabis Grow Lights
What is Par and why is it important?
This is a sample of one of the many different grow light bars that are available.
PAR stands for Photosynthetic Active Radiation. What does that mean? Well, let’s break it down:
In scientific terms, light has properties of both photons and waves and in the spectrum of visible light. The usable light that plants can absorb is used for photosynthesis.
In simple terms: grow lights (that mimic the light of the sun) gives off tons of wavelengths (colors) of light when it shines. However, plants will only absorb some of those wavelengths and use them to eat. The rest of those wavelengths are reflected from the plants.
PAR is the amount of light that’s usable to plants- those wavelengths that will be used for photosynthesis. Just like the difference between a growing area and a canopy, PAR is not the measure of all of the light a grow light gives off, but the measurement of the wavelengths plants will absorb.
PPF is photosynthetic photon flux. PPF measures the total amount of PAR that is produced by a lighting system each second. This measurement is taken using a specialized instrument called an
integrating sphere that captures and measures essentially all photons emitted by a lighting system. The unit used to express PPF is micromoles per second (μmol/s).
This is probably the second most important way of measuring a horticulture lighting system, but, for whatever reason, most lighting companies don’t list this metric.
It is important to note that PPF does not tell you how much of the measured light actually lands on the plants, but is an important metric if you want to calculate how efficient a lighting system is at creating PAR.
PPFD is photosynthetic photon flux density. PPFD measures the amount of PAR that actually arrives at the plant, or as a scientist might say: “the number of photosynthetically active photons that fall on a given
surface each second”. PPFD is a ‘spot’ measurement of a specific location on your plant canopy, and it is measured in micromoles per square meter per second (μmol/m2/s). If you want to find out the true light intensity of a
lamp over a designated growing area (e.g. 4’ x 4’), it is important that the average of several PPFD measurements at a defined height are taken. Lighting companies that only publish the PPFD at the center point of a coverage
area grossly overestimate the true light intensity of a fixture. A single measurement does not tell you much, since horticulture lights are generally brightest in the center, with light levels decreasing as measurements are
taken towards the edges of the coverage area. (Caveat Emptor: Lighting manufacturers can easily manipulate PPFD data. To ensure you are getting actual PPFD values over a defined growing area, the following needs to be
published by the manufacturer: measurement distance from light source (vertical and horizontal), number of measurements included in the average, and the min/max ratio). Fluence always publishes the average PPFD over a
defined growing area at a recommended mounting height for all of our lighting systems.
Photon Efficacy refers to how efficient a horticulture lighting system is at converting electrical energy into photons of PAR. Many horticulture lighting manufacturers use total electrical watts or watts per
square foot as a metric to describe light intensity. However, these metrics really don’t tell you anything since watts are a measurement describing electrical input, not light output.
If the PPF of the light is known along with the input wattage, you can calculate how efficient a horticulture lighting system is at converting electrical energy into PAR. As a reminder, the unit for PPF is μmol/s,
and the unit to measure watts is Joule per second (J/s), therefore, the seconds in the numerator and denominator cancel out, and the unit becomes µmol/J. The higher this number is, the more efficient a lighting system
is at converting electrical energy into photons of PAR.
To learn more about our cannabis grow lights, contact us at Info@eFederalSystems.com