Guide to photosynthetically active radiation (PAR)

There are several different terms that are essential to understanding grow lighting and the optimisation of plant yields across multiple climates, grow spaces and plant types. One of the most important of these is photosynthetically active radiation, commonly referred to as PAR. In a recent blog post, Light Science Tech touched on the terms PAR, PPF and PPFD and their importance to the grower, but in this piece they’re digging deeper into PAR and how this fundamentally influences the grower, the plant and the product.

PAR of 400-700nm is one of the most important sources of energy for the plant, but it has to be consistently adapted to ensure that it isn’t too high or too low otherwise it will have a negative impact on plant growth and health. In the natural day, PAR is never constant – it varies based on environmental factors such as location, season and time of day. The plant has therefore evolved to constantly adapt to these changes, balancing the need to convert radiation energy with the need to protect against photoinhibition.

The colour spectrum, LEDs and PAR
Over the past few years, light-emitting diodes (LEDs) have become increasingly valued by growers due to their versatility and longevity. They can be used across several colour spectrums to ensure that plant growth is optimised in variable conditions, and they can play a role in optimising PAR. In a paper written by Paul Kusuma, P. Morgan Pattison and Bruce Bugbee entitled ‘From physics to fixtures to food: current and potential LED efficacy’, the authors explain the value of LED lights across multiple colour spectrums for PAR, including far-red photons, in transforming plant quality and growth cycle.

What this means for growers is that LED lights can be optimised beautifully to the right PAR throughout the plant lifecycle to ensure the right results. As the photons that sit within PAR are weighed equally across the whole spectrum, the right LED grow light alignment would then weigh the photons of the lamps according to the plants’ spectral sensitivity curve to ensure optimal light wavelengths.

These adjustments can have a significant impact on the plant health and quality, so light has to be carefully managed to ensure equal distribution across the plant at the right temperature and at the right distance. This is where a deep understanding of PAR and PPF and PPFD can make a significant difference to crop, yield and grower.

Optimise
You can optimise your LED grow lights for PAR but it’s worth working with an expert such as Light Science Technologies to support you in achieving the correct light, heat and distance. Leveraging the expertise of people who understand the innate workings of PAR and the relevance of wavelength, spectrum and light distribution can make all the difference to your investment.

You can achieve measurable percentage growth improvements with LED grow lighting that is designed to ensure the photon wavelength matches your growth stage and your crop.