The amplitude of light (or intensity) is important to almost all professional cannabis growers, but the advertising surrounding lighting products when it comes to amplitude is confusing. Intensity matters because even if you have the right spectrum, do you have the right amount of that spectrum? If there’s not enough light, plant growth can stall and the plant may die. If there’s too much light, the plant may experience permanent damage and stunting.
So where is the “just right” zone? Well, let’s start with figuring out what units we want to use first.
Lighting amplitude can be measured with multiple different units. For human applications (such as home or office lighting), the unit we typically use is lumens. This unit is inappropriate for growing plants, because the human eye perceives green light very intensely and violet and red light rather dimly. The opposite is true for plants.
Here is where PAR can come in handy. Since PAR already talks about the wavelengths relevant to plants, we can now add a measurement of the intensity of PAR. These intensity measurements are typically Photosynthetic Photon Flux (PPF) or Photosynthetic Photon Flux Density (PPFD). PPF measures the amount of photosynthetically active light being given out by a luminaire at any given moment, and PPFD measures how tightly focused the PPF is in a target area. In other words, PPF measures the total amount of light originating from your luminaire, PPFD measures how much of that light is being concentrated onto the plant surface.