Understanding Photosynthetic Radiation Terms
A Brief History
In the 1960s, scientists used a device called a pyranometer to measure sunlight. This device captured all shortwave radiation, which includes a range of wavelengths. However, only a specific part of this light, called Photosynthetically Active Radiation (PAR), helps plants grow.
Back then, PAR was measured in watts per square meter. While this method was useful, it didn’t accurately show how much light actually helps plants.
The Shift to Measuring Photons
As research improved, scientist Keith McCree suggested a better way: instead of measuring energy, we should count the number of light particles, or photons, involved in photosynthesis. This led to the term Photosynthetic Photon Flux (PPF), measured in micromoles of photons per square meter per second. This was a clearer way to understand how much light plants use.
However, many people still mixed up PAR and PPF, which caused confusion.
Clarifying Terms: PPF vs PPFD
Today, there’s a move toward clearer language. PPF measures the total number of photons from a light source, without considering the area. On the other hand, Photosynthetic Photon Flux Density (PPFD) takes the area into account, which is important for knowing how much light is available for plants.
To put it simply, if you only know how many raindrops fell (PPF), you won’t know how much rain actually reached your garden (PPFD). That’s why PPFD is now used more often in research.
Changing Definitions
As scientists learn more about how plants grow, they are also changing what they consider to be useful light. Traditionally, light between 400 and 700 nanometers was seen as important, but new research shows that far-red and some ultraviolet light also help plants. This has resulted in a new term: Photon Flux Density (PFD), which includes a wider range of light.
Conclusion
In summary, as our understanding of light and its effects on plants improves, clear terminology is essential. While terms like PAR, PPF, and PPFD were often used interchangeably before, growers should now focus on using PPFD for clarity and understanding how light impacts plant growth.
