What is the principle by which LED plant grow lights promote plant growth?

Why can LED plant grow lights promote plant growth?
Light has two kinds of effects on plant grow lights,

one is an indirect effect,

and the other is a direct effect.

 (1) Indirect effect, namely photosynthesis. Since plants must grow under relatively strong light for a certain period of time to synthesize enough photosynthetic products to meet their growth needs, it can be said
that the demand of photosynthesis for light energy is a "high-energy reaction."

 (2) Direct effect refers to the effect of light on plant morphogenesis. Since photomorphogenesis can be satisfied by only a short period of weaker light, the demand of photomorphogenesis for light
is a "low-energy reaction."

 The direct effects of light on plant growth are mainly shown in the following aspects:

 ① Germination of light-requiring seeds. The germination of light-requiring seeds is affected by light quality; usually red light promotes the germination of light-requiring seeds, while far-red light inhibits it.

 ② Greening of etiolated seedlings. Plants grown in darkness become etiolated, showing states such as pale yellow stems and leaves, slender stems, and small, unexpanded leaves. If the etiolated plant is exposed to light, the
stems and leaves gradually turn green; this is mainly because the formation of chlorophyll and chloroplasts requires light.

 ③ Control of plant morphology. Leaf thickness and size, stem height, the number and length of branches, and the root-to-shoot ratio are all related to light intensity and light quality. For example, UV-B can destroy the molecular structure of nucleic acids,
denature various proteins, oxidize IAA, and hinder cell division and elongation, thereby dwarfing the plant and reducing leaf area.

 ④ Day length affects plant growth and dormancy. The vast majority of perennial plants are promoted to grow under long-day conditions and induced into dormancy under short-day conditions.

 ⑤ Phototropic movement of plants. Phototropic movement is the bending growth phenomenon of plant organs caused by unilateral light irradiation; usually stems and leaves have positive phototropism, while roots have negative
phototropism.

 LEDs have many characteristics different from other electric light sources, which also makes them the first choice for energy-saving and environmentally friendly light sources. LEDs used in the field of plant cultivation also show the following characteristics:
rich types of wavelengths, which exactly match the spectral range of plant photosynthesis and photomorphogenesis; narrow spectral half-width, allowing pure monochromatic light and composite spectra to be obtained in combinations as needed,
; light of a specific wavelength can be concentrated to illuminate crops evenly; not only can it regulate crop flowering and fruiting, but it can also control plant height and the nutritional composition of plants; the system generates little heat,
occupies little space, and can be used in multi-layer three-dimensional cultivation systems. Waterproof LED plant lights and aquarium lights have product advantages, achieving low heat load and miniaturization of production space; in addition, their extremely strong durability also reduces operating costs. Because of these
remarkable characteristics, LEDs are very suitable for plant cultivation in controlled facility environments, such as plant tissue culture, protected horticulture, factory seedling production, and space ecological life support systems.

 Plant growth patterns must require sunlight, and LED plant grow lights use the principle of sunlight and use artificial light instead of sunlight to provide a growing and developing environment for plants,
a type of lighting fixture. Therefore, they can better promote the growth of light-loving plants at night or under dark conditions.