What Is ePAR — And Why It Might Replace PAR in the Future

When growers talk about plant lighting, the term PAR (Photosynthetically Active Radiation) is almost always part of the conversation. For decades, PAR — the range of light between 400 nm and 700 nm — has been the gold standard for measuring the light plants use for photosynthesis.

But plant science has advanced, and researchers now know that the traditional PAR range is only part of the story. A new concept called ePAR (extended PAR) is gaining ground — and it could soon become the preferred way to measure light for plant growth.

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PAR vs. ePAR: What’s the Difference?

• PAR (400 – 700 nm): Includes blue, green, and red light that plants use for photosynthesis.
• ePAR (400 – 750 nm): Expands the range to include far-red light (700 – 750 nm), which scientists now know plays a key role in plant growth when combined with other wavelengths.

The idea behind ePAR is simple: although far-red light alone is not highly efficient for photosynthesis, it can boost the efficiency of red and blue light when used together. This synergistic effect — known as the Emerson effect — means plants can produce more energy from the same total light when far-red is included.

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Why Far-Red Light Matters

Far-red photons may not directly drive photosynthesis as strongly as red or blue photons, but they influence how plants grow in important ways:

• Enhanced Photosynthesis – Far-red light increases the overall rate of photosynthesis when combined with shorter wavelengths.
• Improved Canopy Penetration – Longer wavelengths penetrate deeper into plant canopies, delivering light to lower leaves.
• Morphological Effects – Far-red encourages leaf expansion, stem elongation, and improved light capture across the canopy.

In other words, including far-red light can make plants more efficient at using the light they receive — even if the total light level stays the same.

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Why ePAR Is Gaining Popularity

Because it captures a more complete picture of how plants use light, ePAR is becoming a preferred metric for advanced horticultural lighting. More and more LED manufacturers and research institutions now provide ePAR output data rather than just PAR.

Here’s how ePAR benefits growers:

• More accurate light planning — especially in controlled environments.
• Better comparison between fixtures — since some emit far-red while others don’t.
• Deeper insights into plant response — beyond basic photosynthesis.

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PAR Isn’t Going Away — But ePAR Is the Future

PAR remains useful, especially for comparing lighting systems and understanding basic plant lighting needs. But as our understanding of plant biology evolves, ePAR offers a more complete and realistic picture of how light powers growth.

If you’re designing lighting systems for high-value crops, vertical farms, or research applications, it’s time to look beyond traditional PAR and start thinking in ePAR.

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Tip: AquaHorti’s advanced PAR meters are designed with future-ready measurement capabilities — helping growers track, log, and optimize light across the full photosynthetic spectrum.