- Ideal PPFD Levels
- Measuring PPFD
- Factors Limiting Lighting
The yield or output of an indoor cannabis flower room is limited by the size of the room or available space. This means that the size of your cultivation space will also determine the amount of light that is needed. Photosynthetic Photon Flux (PPF) and Photosynthetic Photon Flux Density (PPFD) levels can help growers determine the best lighting solutions for their indoor cultivation spaces. When the amount of lighting is insufficient in a flower room, the result is a lower quality cannabis and lower quantities. If plants receive too much light at too high of an intensity then they can receive light burn. High-Intensity Discharge (HID) lights are commonly advertised for a certain growing space based on the lamp’s wattage, for example a 1000w HID light is recommended by light manufacturers to be optimal in a 5’x5’ grow space. Instead of using wattage to determine how much light is needed, growers should measure the amount of light the plant canopy is receiving. Remember, HID lights give off light within the 400nm-700nm light spectrum range which is considered Photosynthetically Active Radiation (PAR). This PAR light specifically is what is important because plants need light that is within this range to grow. The light is measured in a unit called photons. It’s not just about getting adequate lighting, but specifically getting adequate PAR photons.
Ideal PPFD Levels
The ideal PPFD levels are between 700-900 µmol (PPFD) for indoor cultivation spaces and there should not be any spots on the top of the canopy that is receiving less than 500 µmol (PPFD). Plants that receive less than 500 µmol (PPFD), will produce smaller buds with more “larf” or less-dense and leafy buds when compared to flowering cannabis plants that receive ideal PPFD levels. Many growers may try to add more light than necessary to an indoor grow space to provide as many photons of light to their plants, but there is also a limit to the density of photons that cannabis plants can use. Larger cannabis plants can handle higher levels of PPFD, up to 1500 µmol (PPFD), if enough supplemental CO2 is applied to the grow space on a consistent basis and additional environmental factors such as temperature and relative humidity are also optimal. Their light intake can be somewhat limited by the amount of ambient CO2. If PPFD levels exceed 2000 µmol (PPFD) indoors, then it is possible that the quality and quantity in yields could be diminished in extreme cases. Excessive levels of PPFD can eventually lead to plant tissue damage. Plants will try to protect themselves through photo protection responses as a result of excessive lighting. Photoinhibition decreases the rate of photosynthesis as a result of light stress. Chlorosis will eventually set in when photoinhibition no longer effectively protects a plant.
Wattage is not the correct metric to measure the amount of usable light for plants. Instead, growers should focus on using Photosynthetic Photon Flux (PPF) and Photosynthetic Photon Flux Density (PPFD) to measure the amount of usable light for plants. PPF is the measurement of PAR photons and PPFD is the measurement of the PAR photon density in a certain space. This applies to all types of lights used in cultivation HID, LEC, and LED.
Factors Limiting Lighting
There are other environmental factors that can limit a plant’s uptake of light for photosynthesis. The environment’s temperature, CO2 levels, and relative humidity are all factors that can affect a plant’s rate of photosynthesis. Not only environmental factors, but a plant’s overall health can also affect its rate of photosynthesis.
Chandra, Suman, et al. (2008) “Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions”. Physiology and Molecular Biology of Plants v.14, i. 4.
Chandra, Suman, et al. (2008) “Light dependence of photosynthesis and water vapor exchange characteristics in different high Δ9-THC yielding varieties of Cannabis sativa L.”. Journal of Applied Research on Medicinal and Aromatic Plants, v.2, i.2, June 2015, pp.39-47.