WATTS vs PAR vs PPF vs PPFD

The terms wattage, PAR, PPF and PPFD are critical for the understanding of light output, specifically for indoor growing. Many manufacturers list wattage incorrectly and may not even allude to PAR nor PPF output. This information is paramount to deciding which light is best for your needs.

Electricity is a measurement of power, typically measured in wattage or joules. Electrical consumption is measured at the wall (where the device is plugged into the electrical source) and refers to the amount of power used per hour.

PAR is “photosynthetically active radiation” and refers to the part of the visible light spectrum that plants use to drive photosynthesis. This is typically in the 400-700 nM range, exceptions being UV light which is present at wavelengths <400 nM and IR (infrared radiation) > 800 nM. Infrared radiation is commonly referred to as heat.

PPF (photosynthetic photon flux) refers to the total photosynthetically usable light (in photons) emitting from a luminaire. Total PPF output, however, does not equate to the amount of power usable by your crop. Many lighting manufacturers use optics such as lenses or reflectors in order to shape the light output so that most of it goes towards the canopy. The usage of optics such as lenses and reflectors cause losses in efficiency. Lenses and reflectors absorb photons and can cause upwards of 10-15% decreases in overall PPF present @ canopy level.

PAR maps are a good tool for understanding how much PPF is present at a given operating height across a defined area. A light that is specified to cover a 4x4 area should have a map stating the PPF levels across the entire area thus giving a good understanding of photon power not only in the center, but most importantly at the edges and corners where levels are typically lower. PAR Maps are traditionally measured at a given height above canopy. As the light height above canopy increases, PAR mapping values will become more “diluted” as the total PPF is spread over a larger area. Lower hanging heights typically have stronger PAR values over a smaller coverage area.

PPFD (photosynthetic photon flux density) is a calculated value and is measured in µmol/m²s. This refers to the amount of light falling on a given coverage area every second. For cannabis, PPFD levels of 300-500 µmol/m²s are consistent with strong vegetative growth and levels of 900-1000 µmol/m²s for flowering. It is worth noting that in CO2 enhanced environments, due to the additional carbon present which enhances photosynthetic activity, plants can utilize up to 1200 µmol/m²s.

PPF is not PPFD, although the two are oftenconfused, they are related. For example, PPF over a 3x3 area will result in a much higher PPFD amount than the same amount of PPF over a 4x4 or 5x5 area. As such, it is important to know not only the total amount of power output from a light (PPF), but also the amount of density over the intended coverage area (PPFD). PPFD is characterized by square meters of coverage. A 3’x3’ area is roughly .9 m² whereas a 4x4 area is roughly 1.5 m². PPF is divided by coverage area (in meters) to give a corresponding PPFD value. This concept is like that of water emitting from a garden hose. When the nozzle setting is set to ‘jet’, there is an intense amount of water focused on a smaller area. With the same amount of water emitted on a softer setting, such as ‘shower’, the same amount of water covers a larger area, at a lower amount of water per square foot.