The Optimal Color Spectrum for Cannabis

- Nov 11, 2019-

Like many green plants, cannabis contains concentrations of two forms of chlorophyll, A and B. Each of those forms reacts differently to different wavelengths of light in the color spectrum. As cannabis cultivators improve their understanding of how different parts of the light color spectrum affect their crops and strains, they will need advanced lighting systems for cannabis cultivation facilities that enable them to customize and specify the light spectrum for better plant growth.

That technology allows growers to adjust the relative concentration of different color spectrum components to match a plant’s lighting needs with pinpoint accuracy at every stage of the plant’s growing cycle. How this might work and the color spectrum combinations that a grower might use are readily illustrated with cannabis cultivation.

Much of the research and development of how the lighting color spectrum affects plant growth has focused on cannabis because of the explosive growth of the indoor commercial cannabis cultivation industry. A cannabis cultivator will generally adhere to a certain pattern of spectrum combinations:

Cultivators initially want a cannabis plant to establish a strong root structure during its germination and seedling stage. That root structure can be enhanced with different ratios of red and far-red light with wavelengths at 660nm and 730nm.

With more far-red light, cannabis plants will grow taller and have fewer leaf nodes. The plant actually wants more red than far-red light, and it has evolved through natural processes to grow taller in order to get its share of red light when it is growing in crowded fields of other plants that are also reaching for red light. A cultivator can shift relative percentages of red and far-red light to achieve the optimum height and leaf ratios as the cannabis plants develop their vegetation.

Cannabis plants (like other plants) also need cycles of day and night for proper development. LED grow light systems are ideal for replicating these cycles because they can be switched on and off almost instantaneously, with no warm-up phase. A cultivator can factor these grow light cycles into the color spectrum variations that are used throughout the plant’s lifespan.

As the plant approaches its flowering stage, it will need a more blended concentration of all wavelengths of light in the color spectrum. Budding and flowering is marked by many complex biochemical processes in the plant, and those processes all have different color spectrum needs.


When the cannabis plants are in their late flowering phase and are moving toward harvest, light in the blue spectrum can be reduced.

Color spectrum variations are one of several related variables that a cultivator will want to control for better quality cannabis production. The intensity of the light and the temperature and humidity of the growing environment should also be controlled for optimum results.