There is a close relationship between light and plant development. You should know that some plants grow quite differently depending on the light intensity but also in terms of the composition of light, this is the spectral composition.

The action of light on plants is divided into two:

It is the mechanisms of photosynthesis and photomorphogenesis.

A plant is sensitive to light even before its first leaves (or other photosynthetic apparatus).

Why the light emitted by the horticultural LED light is pink / purple?

Horticultural LED light is colored, not for an esthetic purpose but because the main active pigments in photosynthesis are the chlorophyll pigments. Chlorophylls A and B are sensitive to blue wavelengths between 400 and 500 nm and the red between 630 and 700nm.

These wavelengths are for the plant’s main energy source. Other wavelengths only a slight influence on the photosynthesis but have a role in the photo-morphogenesis

The majority of the light emitted by the LED is horticultural pink / purple to maximize photosynthesis.

Other wavelengths (emitted by LED monochromatic other than blue / red or white LEDs) have a role in the photo-morphogenesis and thus control the development of physical features of the plant: the inter-node distance, the thickness of the leaves, branches, and the start of the blooming. It is even possible to stagnate the development of a plant with a specific spectrum. This can be useful for the production of ornamental plants to delay their placing on the market.

For more understanding…

Photoreceptors: The photoreceptor cells are capable of receiving photons and react to the stimulation. In plants, the phytochromes are photoreceptors, but also some proteins.

Phytochromes: The phytochromes are plant photoreceptors. They are involved in the synthesis of chlorophyll, flavonoids and stimulate the production of carotenoids. The phytochromes change state according to the light they are subjected to. They affect plant growth. The phytochromes are sensitive to red, cryptochromes and phototropins are sensitive to blue and ultraviolet. The phytochrome sensitive to red through two forms depending on the wavelength it is subjected to. It goes from inactive to active state when subjected to 660nm wavelength (Pr absorption peak; phytochrome red) to turn into Pfr (absorption peak of 720nm Pfr; phytochrome far red). They have a role in photo-morphogenesis.

Cryptochrome: This is a photoreceptor sensitive to blue / UV-A. It has a mediating role in phototropism, there is still little studied. As phototropins, it plays a role in maintaining circadian rhythm and is sensitive to magnetic fields.

Phototropines: This is a sensitive blue photoreceptor and plays a role in phototropism (the fact that a plant grows, bowing toward the light source). This is a reaction involving the auxins which when the side of a rod receives less light than the other, it lengthens. As cryptochromes, they play a role in the maintenance of circadian rhythm and are sensitive to magnetic fields.

Carotenoids: Absorbs a lot green light and less yellow / orange light.

Xanthophilic: This is a part of the carotenoid pigment. He is responsible for the yellow color of egg yolks. It is present in high concentrations in the majority of plants. It has a protective role when the light intensity is greater than the absorption capacity of the plant.