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PAR & terminogy

Photosynthetically Active Radiation (PAR) is a critical concept in plant biology and horticulture, referring to the range of light wavelengths that plants can use for photosynthesis. Specifically, PAR encompasses light in the wavelength range of 400 to 700 nanometers (nm), which includes the visible spectrum of light from violet to red.


Key Characteristics of PAR


1 Spectrum Range:


Violet to Blue (400-500 nm): This part of the spectrum is crucial for vegetative growth. Light in the blue range is absorbed by chlorophyll and carotenoids, which are important for photosynthetic activity and regulating plant growth.

Green (500-600 nm): Although less effectively absorbed by chlorophyll, green light penetrates deeper into the leaf tissues and can contribute to photosynthesis.

Red (600-700 nm): Red light is highly efficient for photosynthesis, promoting flowering and fruiting. It is absorbed by chlorophyll a and b and is crucial for the later stages of plant development.

2 Photosynthesis Efficiency:


Chlorophyll A and B, the main pigments involved in photosynthesis, absorb light most efficiently in the blue (430-450 nm) and red (640-680 nm) regions. These wavelengths drive the light-dependent reactions of photosynthesis, where light energy is converted into chemical energy.

3 Measurement:


PAR is measured in micromoles of photons per square meter per second (µmol/m²/s). This unit indicates the number of photons in the PAR range that fall on a given area each second, directly correlating with the light available for photosynthesis.


Importance of PAR in Horticulture

Understanding and optimizing PAR is essential for greenhouse lighting systems to maximize plant growth and efficiency. Here’s why:


1 Optimal Plant Growth:


Providing light that falls within the PAR spectrum ensures that plants receive the necessary wavelengths to drive photosynthesis, leading to healthier and faster growth.


2 Energy Efficiency:


By focusing on the PAR spectrum, particularly the red and blue wavelengths, horticultural lighting systems can maximize the efficiency of photosynthesis. This targeted approach reduces energy waste compared to broad-spectrum or non-optimized lighting systems.


3 Crop Yield and Quality:


Enhanced control over the light spectrum allows growers to influence various aspects of plant development, such as vegetative growth, flowering, and fruit production. This can lead to higher yields and improved crop quality.


Tailored Lighting Solutions:


Advanced LED grow lights can be designed to emit specific PAR wavelengths, tailored to the needs of different plant species and growth stages. This customization helps optimize growth conditions for a variety of crops.

Practical Applications of PAR

In practical terms, growers can use PAR meters to measure the intensity of photosynthetically active radiation in their greenhouses, ensuring that their plants receive adequate light for optimal photosynthesis. Additionally, modern LED grow lights can be fine-tuned to provide specific PAR spectra, allowing precise control over the light environment.



Photosynthetically Active Radiation (PAR) is a fundamental concept for optimizing plant growth in controlled environments. By focusing on the 400-700 nm range, and particularly the blue and red wavelengths, horticultural lighting systems can significantly enhance photosynthetic efficiency and crop productivity. Understanding and utilizing PAR allows growers to design more effective lighting strategies, leading to better plant health, increased yields, and more sustainable energy use.