PPF (Photosynthetic Photon Flux) and Color Temperature

All lights emit a color temperature which is measured in kelvins (K). This value refers to the spectral distribution, or more simply put, the relative amount of each color in the rainbow that makes up white light. PPF measures the amount of photosynthetically active photons of light, or the “photosynthetic power” of a light.

Depending upon the stage of growth, plants require differing amounts of energy for growth. This energy is measured in µmol/m²s as defined over a given coverage area. Young cannabis plants need up to 300-500 µmol/m²s for good vegetative growth and flowering cannabis will require much more power, up to 800-1000 µmol/m²s. As a result, PPF is not a good indicator of power since it will give stronger values over a smaller coverage area. For example, flowering a 2x2 area requires almost 2x the amount of energy as vegetative growth over the same size area. PPFD (Photosynthetic Photon Flux Density) is the controlling factor in a plant's overall growth and flower/fruit dry weight yield. PPFD is the energy associated with photosynthetic activity and the plant's ability to convert sugars to flower mass. In the absence of enough PPFD, a flower will oftentimes be characterized as “airy” or “larfy” and lacking in total overall mass and density. As such, PPFD should always be the primary consideration in selecting a light for the intended phase of growth (vegetative, flowering, or full cycle usage).

Many LED lights have dimmers which allow a grower to control the total amount of energy consumed @ the wall, and subsequently the total PPF emitted from the light. This is helpful when using the same light for full cycle growth (vegetative and flowering in the same space). Perpetual grows refer to the vegetative stage maintained in a separate area from flowering, allowing the same light to be used over different coverage areas with differing power levels. For example, a light used to cover a 4x4 area for vegetative growth dimmed to 50% will cover the same size area for flowering @ 100% output. Dimming effectively reduces the amount of electricity consumed and will also increase efficiency.

Color temperature influences photomorphogenic influences on a plant. Increased red spectral output during vegetative stages of growth can cause longer internode spacing, or “stretch.” Higher levels of blue spectral output during vegetative growth will enhance leaf production in vegetables and maintain a shorter style of plant growth owing to shorter internode spacing. Increased red spectral output during flowering will result in a tighter flower/bud structure producing a denser product, but not necessarily affecting dry weight yield. Dry weight yield being a function of PPFD and color temperature being a function of flower “style.”

For full cycle growth, or growing from seed/clone up through harvest, most growers prefer a more balanced amount of blue vs red spectral output such as 3500K. This color temperature has peaks in both the blue and red spectrum giving it characteristics suitable to all stages of cannabis growth.