The ultraviolet spectrum invisible to the human eye is outside the PAR range (100nm-400nm). About 10% of sunlight is ultraviolet, and like humans, plants can also be damaged by overexposure to ultraviolet light. Although the benefits of using ultraviolet light in horticulture are still under research, ultraviolet light usually brings deeper purple-in fact, a small amount of ultraviolet light can have a beneficial impact on color, nutritional value, taste, and aroma. Studies have shown that using controlled amounts of ultraviolet light can also reduce environmental stress, fungi, and pests. Research has shown that using UV-B light can increase tetrahydrocannabinol and other cannabinoids in cannabis.
The blue light spectrum LED greenhouse lights are widely responsible for improving plant quality-especially in leafy crops. It promotes the opening of stomata-allows more carbon dioxide to enter the leaves. The blue light drives the peak of chlorophyll pigments needed for photosynthesis. This is crucial for seedlings and young plants in the nutritional stage because they build a healthy root and stem structure-especially important when stem extension must be reduced.
Compared with the red or blue spectrum, the green waveband of led greenhouse grow lights are less important for plant photosynthesis because it is easily absorbed by chlorophyll. Nevertheless, green is still absorbed and used for photosynthesis. In fact, only 5%-10% are reflected- the rest are absorbed or transmitted to lower places! In the greenhouse, due to the presence of sunlight, the importance of supplementing the green light spectrum with LED growth lights is lower than for crops grown only indoors (such as cannabis or vertical crops).
It is well known that red light is the most effective spectrum to promote photosynthesis because it is highly absorbed by chlorophyll pigments. In other words, it is located at the peak of chlorophyll absorption. Red light wavelength promotes stem, leaf, and overall nutritional growth-but the most common thing is the large stretching of leaves and flowers. It must be paired with blue light to offset any excessive stretching, such as deformation of stem elongation. It is important to consider that although red is the most sensitive spectrum to plants, its effectiveness will truly come into play when combined with other PAR wavelengths.
There are several ways in which far-red light affects plant growth—one is by initiating avoidance response. At around 660nm (deep red), plants sense the bright sunlight. From 730 nanometers and above, the ratio of far-red light to red light is higher, and plants will detect “shadows” of light from leaves of other plants or higher up in the canopy, which will result in stem and leaf stretching. Far-red
led greenhouse grow lights is useful for promoting flowering and can increase fruit yield in some plants. In short-day plants like cannabis, which rely on long periods of darkness, 730nm can be used to promote flowering at the end of the light cycle. Many growers are experimenting with bursts of red light to interrupt the dark cycle and promote growth and flowering.