Understanding the McCree Curve is fundamental in plant biology, horticulture, and photobiology.
This curve, named after plant physiologist William A. McCree, visually represents the efficiency of various
light wavelengths in driving photosynthesis and influencing plant growth. It is a crucial concept for tailoring
artificial lighting in indoor gardening and greenhouse cultivation to optimise plant development.
The McCree Curve is a graphical depiction of the relationship between light spectrum regions and
their effectiveness in promoting photosynthesis. Covering the visible light spectrum (400-700 nanometers),
it sheds light on how efficiently plants utilise different light colours, particularly focusing on blue (400-500 nm),
red (600-700 nm), and green (500-600 nm) light.
Blue Light (around 440-460 nm): The McCree Curve highlights a substantial peak
in photosynthetic efficiency in the blue spectrum, indicating that plants efficiently
use blue light for photosynthesis, especially during chlorophyll energy absorption.
Red Light (around 640-680 nm): Another peak is observed in the red spectrum,
crucial for chlorophyll absorption during photosynthesis. Red light plays a vital
role in the formation of energy-rich compounds like adenosine triphosphate (ATP).
Green Light (around 510-570 nm): Surprisingly, the McCree Curve reveals lower photosynthetic efficiency
in the green spectrum. While plants don't waste green light, they primarily reflect it, explaining why
they appear green to our eyes.
● Lighting Design: The McCree Curve informs the design of lighting systems emitting an optimal balance of blue and red light,
promoting robust plant growth from seedlings to flowering.
● Growth Stages: Adjusting the light spectrum based on growth stages maximises efficiency.
For instance, more blue light benefits vegetative growth, while red light is crucial during flowering.
● Energy Efficiency: Growers can use energy more efficiently, reducing associated costs,
by aligning lighting systems with the insights gained from the McCree Curve.
● Crop Selection: The McCree Curve aids in selecting crops, helping growers choose
species that respond well to the light spectrum provided by their lighting system.