Your crops need light. Whether its from the sun or artificial LEDs to photosynthesize, grow, and produce food. So what kind of light do plants need? Plants use a specific range of the light spectrum known as PAR. Before going further, lets discuss this spectrum and why its key to successful yields in your farm.
Photosynthetically active radiation (PAR) - PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) or infrared to near-ultraviolet. This is the light spectrum that drives photosynthesis. When we talk about PAR for LED lights, we are referring to the type of light needed for photosynthesis.
Then we have the term full spectrum. The industry refers to "full spectrum" as LEDs that emit lights that cover the full PAR spectrum. Full spectrum lights will look white.
Photosynthetic photon flux (PPF) - Is the measure of the total amount of PAR that is produced by a light every second. PPF is measured in micromoles per second (μmol/s). Specialized instruments called an integrated sphere can be used to measure all photons emitted from a grow light. It is an important measurement when wanting to understand how efficient a light is at creating the PAR.
Photosynthetic photon flux density (PPFD) - Is the measure of the amount of PAR that actually gets to the plant. It's also known as a spot measurement since its location based relative to your plant foliage. PPFD is measured in micromoles per square meter per second (μmol/m²/s). To find the true light intensity of a light over a designated growing area, you should take the average of several measurements at a defined height. This is because grow lights don't emit light evenly across their entire usable work area. This has to do with the clustering of LEDs towards the center of your grow light collectively producing a higher density of light vs a thinner density of LEDs towards the edge of your grow light. Because the difference in PPFD can be quite large from the center to the edge of the coverage area, some companies resort to not publishing their full PPFD map and just give you their single highest measurement.
Photosynthetic photon efficacy (PPE) - Refers to how efficient a light is at converting electricity into photons or PAR. Many manufacturers use total watts, but don't express what the actual conversion rate of those watts are to pure light. You can calculate how efficient your grow light is if you know your PPF and the rated wattage of the light. Wattage is measured in Joules per second (J/s). Photon efficacy is measured by dividing your PPF by your wattage. This gives you a PPE in μmol/J.