What are PAR values?


Have you ever wondered what the PAR, or Photosynthetically Active Radiation, values are when comparing LED lights?

What is PAR?

Plants use a process call photosynthesis (the most important chemical process on Earth) as a source of energy to make food molecules from carbon dioxide and water.  The only type of light which enables photosynthesis is defined as Photosynthetically Active Radiation (PAR): the narrow band of light between 400nm – 700nm.  Light outside of this range is not photosynthetically active and will not generate greater biomass for those seeking improved yield.

What is PPF?

An electronic light source converts electrons into photons. Lights for human vision measure output with lumens (measured in lux or footcandles). Lights for photobiological reactions measure output with photosynthetic photon flux (PPF) or the rate at which the light source emits in the photosynthetic region.

Another way of stating it is: PPF tells us how much PAR a light source emits.

What is PPFD?

Where PPF measures total PAR output of a lighting system, Photosynthetic Photon Flux Density (PPFD) measures how much of that light is delivered to a given area. Another way of stating it is the measurement of PAR delivered to a specific area in a specific period of time. It is expressed as micromole-per-meter squared-per second (μmol/m2/s).

This measurement informs us of the amount of light being delivered to a crop to enable photosynthesis.

 Apogee is a leading manufacturer of environmental sensors.  One of the most applicable of these sensors to home growing is the quantum sensor designed to measure light (quantum energy) that is used by plants for photosynthesis.  The sensor measures photon flux in the photosynthetically active wavelength range of 389 to 692 nm as the PPFD.

Apogee published this excellent video on the scientific principles of PAR values and their importance when selecting grow lights.

At Indo Products we realize that LEDs are not the Sun or for that matter an HPS bulb.  However, LEDs are a much more cost effective alternative to HPS bulbs. Therefore, we strive to only work with LEDs that emit full spectrum light, with best-in-class light coverage providing home growers year round growing capabilities at a reasonable cost.

Happy growing and enjoy the video, 

The Indo Team