Far-red Light Effects on Long-day Plants

What is long-day plants?

Plants need a period of time in the process of growth and development. If the number of hours of sunlight per day exceeds a certain limit (more than 12 hours), flower buds can be formed. The longer the sunlight time, the earlier the flowering. All plants with this characteristic are called long-day plants, such as asters, echinacea, California poppies, lettuce, spinach, and potatoes, etc.

What is far-red light?

Far-red light is electromagnetic radiation with wavelengths between 700-800nm and it falls between the red and infrared regions of the spectrum. As for human, we will barely see it because it hangs out on the edge of the visible light spectrum. However, to our humble plants, far-red is a game-changer, manipulating both their morphology and ability to photosynthesize. Like UV light, far-red light is regarded as some “forgotten” spectrum.

What effects of FR on long-day plants?

1. Shading effects of 730nm Far Red Light

If a light-loving plant is only illuminated by the deep red light at 660nm, the plant will feel that it is under direct sunlight and grow normally. When it is shaded, it naturally receives more far-red than red light, leading to stem elongation as part of the plant’s effort to avoid shade. That is, it helps the plant grow taller.

2. Flowering induction by 730 nm far-red light

Another important role of 730nm far red light in horticultural lighting applications is that the flowering cycle can be controlled by lighting at 660nm and 730nm, rather than relying solely on the influence of season, which is of great value for ornamental flowers.  

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Evelyn Zhong

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