How do we measure the visual spectrum?
We measure color and color temperature of light sources using the Kelvin scale; The higher the color temperature, the more blue and cool the light becomes; the lower the color temperature, the warmer the light and this is where the red part of the spectrum is located. The Kelvin scale illustrates the color we capture the light in, each color temperature (k) contains an infinite number of light waves to produce the perceived color the specific light has.
We also measure the visual spectrum in nanometers (nm) ranging from 400 to 750 and beyond this scale, infrared and ultraviolet, respectively, are at either end of the scale. Unlike Kelvin, the nanometer measures the specific light wave, of which several light waves combined form a color temperature that can be measured in Kelvin. Each light wave has its own frequency and content of photon energy. Colors with only one light wave are called spectral colors or pure colors.
In order to measure the efficiency of light and the need to cover the plant’s needs, we now move to PAR and PPFD, because a lamp is not necessarily more efficient just because it consumes more watts. Typically, when measuring the light, it will be measured in Lumen (Lux), but this is not optimal when we measure the efficiency of a lamp intended for plant growth. Lumen is the amount of visible light emitted but not necessarily the light that is absorbed by the plant.
The plant’s absorption of light depends on the synergy in the climate; Temperature, humidity and CO2. An example would be a temperature of 26 degrees, an air humidity of 80% and a ppm value of 1400 would allow up to 1500 micromoles in ppfd value intake for your plants. However, we do not recommend over 700 Micromoles because the efficiency of light intake disappears and you will not use the additional energy supply significantly unless you give big amounts of co2 to your plants.
Micromoles that are the yardstick for PAR and PPFD values mean the number of Photons that pass through the measured area. To give a perspective, 1 micromole of light corresponds to just over 62 quadrillion photons.
PAR are all light waves measured within the visual spectrum used for photosynthesis within 400 to 700 nm. PFFD, on the other hand, is the amount of photons that hit a given surface and is typically measured in micromoles per second. second per second square meters within a given time frame.
In other words, the PAR is the amount of light and light waves in a given spectrum whereas PPFD is the amount of energy the plant actually occupies.
After realising this it is important to know that even tho you have 900 umol of light it dosen´t mean the light is very efficient if it contains large amounts of green and yellow which the plant has challenges of absorbing the energy. An efficient use of the light is when you have about 3 times more red than blue color with low amounts of green and yellow because the photosynthesis will be activated much better with this distribution of light.