My area of formal education is heavy in physics and engineering, but this is about you.
I want to educate the consumer on what all these spectral analysis graphs and datasheets mean. This is the spot for that.
Why the name?
When I started thinking about a business name, I thought it would be clever to have the initials of the company mean something in regards to light measurement.
PFD in terms of light measurement means "Photon Flux Density" - which is the number of photons passing through a given area per second and one of the most basic ways of measuring light intensity in an area. I really liked the name "Photon Phantom Designs" so I switched the 'Ph' in Phantom to an 'F' and my company's initials became PFD.
What is a Photon?
For simplicity, we'll call a photon a "packet" of light. Photons are one of the ingredients plants use to make glucose during photosynthesis. (the other ingredients being water and carbon dioxide)
You might be asking "what is a packet of light" - well lets say you had a laser that only emits 660nm red light.....each 660nm photon is a packet of the same amount of energy. 660nm photons happen to have an energy of 1.878eV (electron Volts) - so the if you shine the laser at a detector for any period of time, the total amount of energy given off by the laser will always be a multiple of the 1.878eV because each photon carries exactly that amount of energy. This quantifiable behavior of subatomic and atomic particles is where the field of Quantum Physics gets its name.
The wavelength of a photon determines its energy. A blue photon has inherently more energy than a red photon because it has a shorter wavelength.
Photosynthesis and the McCree Action Spectrum
For the purpose of growing plants we mainly focus on light in the visible range from 400nm (violet) to 700nm (red). This range encapsulates the light spectrum that horticulturists refer to as Photosynthetically Active Radiation, or PAR. The accepted
photosynthetic efficiency of each wavelength in the PAR spectrum is known as the “McCree Action
Spectrum” and was developed by studying the the photosynthesis rate of 22 different plant species over wavelengths from 300nm-8000nm.( K.J. McCree, 1971
Why white LEDs?
The short answer is: we got lucky. A white LED such as a COB is really a blue LED with a phosphorus coating that fluoresces when it's hit with blue light from the COB. This scatters the blue photons across the visible spectrum. Different companies have proprietary phosphors and different phosphors are what make a COB a 3000k CCT or a 6500k CCT. By and large, a 4000k white LED will have roughly the same spectral graph as any other 4000k white LED, so don't be fooled by claims of "our white LED's were specifically tailored to meet the McCree action spectrum" - if there are other color temp LED's or monochromatic LEDs involved then its worth looking into to see what their spectrum looks like.
Recent studies have also called the McCree Action spectrum into question by showing that plants utilize green more than red or blue light when the total light intensity is high enough (about 600 PPFD) (Terashima, et al., 2009). This photosynthesis happens inside the leaf, which is why leaves appear to be green even though they use green light very efficiently. I believe this is why white LED's and also HPS bulbs work so well for growing plants.