top of page

Light Spectrum vs. µmols

Why Selecting an LED Grow Light Goes Beyond High Numbers.

In the ever-evolving landscape of LED grow lights, it's crucial to look beyond the surface when choosing a new fixture. With many lighting companies and innovative horticultural LED lighting fixtures flooding the market, some resort to simplifying their products down to a single number.

Moving Beyond Photon Efficiency. Enter the realm of Photon Efficiency, often referred to as Photosynthetic Photon Efficacy. (PPE). While the acronym may initially sound scientifically impressive, understanding the underlying concepts is key. Delve a little deeper, and you'll find that Photon Efficiency is measured in µmols per Joule (J). For those not well-versed in scientific jargon, this may evoke memories of a classroom setting, but it's an essential metric in the horticultural industry. Unpacking Photon Efficiency. Photon Efficiency is essentially the total light output generated by a fixture (PPF or Photosynthetic Photon Flux) measured in µmols per second, divided by the watts needed to produce that light. It's a ratio that gauges how efficiently a fixture transforms electrical power (Joules) into plant-usable light (µmols).

PPF( Photosynthetic Photon Flux) by Input Power (Watt) is Photosynthetic Photon Efficacy

Not All Photons Are Equal. Photon Efficiency, while a valuable metric, has its limitations. It counts all photons equally, regardless of their position on the light spectrum. Full-spectrum light comprises photons of varying energy levels, from high-energy blue to low-energy red. As Light Intensity (PPFD) Increases, Light Spectrum Plays a Bigger Role. Commercial indoor farmers recognize that delivering a high number of photons is not enough; the quality of light matters. Plants evolved under continuous full-spectrum sunlight, and as light intensity increases, spectral quality becomes crucial for proportional photosynthesis.

light and plant heath

The Emerson Effect. Scientific research, notably by Robert Emerson, emphasizes the significance of multiple colors of light for optimal photosynthesis. UV and far-red light contribute to critical metabolic processes, a concept embodied in ILUMINAR Lighting's iLogic™ LED series. It All Comes Back to PAR. Traditional metrics like Photosynthetic Photon Flux (PPF), PPFD (incident light intensity), and Photon Efficiency all revolve around PAR. However, the definition of PAR has evolved, now including photons between 380 and 760 nanometers. And There’s More… New metrics like ePAR, BPF, BPFD, and BPE are emerging, broadening our understanding of biologically active light. Manufacturers adopting these terms signify a progressive approach.

Light Spectrum with UV & Far Red

Considerations When Choosing an LED Grow Light. Beyond metrics, factors like recommended canopy distance, dimmability, controller compatibility, diode lifespan, variety, and layout, water resistance, form factor, as well as driver and heat sink quality, play crucial roles. In Conclusion. While Photon Efficiency is a valuable metric, a holistic approach considering various factors is essential. If a manufacturer emphasizes Photon Efficiency without providing additional relevant information, asking pertinent questions or exploring alternatives is advisable. For further inquiries, feel free to contact us at We're passionate about discussing these discoveries. Watch the full video:


bottom of page