Principles and Prospects of LED Plant Growth Lights

      After application testing, the wavelength of the plant light is very suitable for the growth, flowering, and fruiting of plants. In general, indoor plants deteriorate over time primarily due to insufficient light exposure. By using LED lights that emit spectra suitable for plant growth, not only can it promote growth, but it can also prolong flowering periods and enhance flower quality. When this efficient light source system is applied to agricultural production facilities such as greenhouses, it can address the drawbacks of insufficient sunlight, which leads to a decrease in taste for greenhouse vegetables like tomatoes and cucumbers. Additionally, it can enable winter greenhouse vegetables to enter the market earlier, around the time of the Chinese New Year, achieving the goal of off-season cultivation.

1. As supplementary lighting, it can enhance illumination at any time during the day, thereby extending the effective lighting period.

2. Regardless of dusk or night, it can effectively prolong and scientifically control the light required by plants.

3. In greenhouses or plant laboratories, it can completely replace natural light to promote plant growth.

4. It completely resolves the uncertainty in seedling growth due to weather conditions and allows for a rational schedule based on the delivery time of seedlings.

Significance of Greenhouse Internal Lighting

It is crucial to understand that the speed of plant growth depends on light intensity—the amount of light radiation absorbed on the plant surface—rather than the number of light sources. Many ask about the significance and methods of greenhouse internal lighting and what type of light source to choose.

The significance of greenhouse internal lighting lies in extending sufficient light intensity within a day. It is mainly used for planting vegetables in late autumn and winter, including rose and chrysanthemum seedlings. Greenhouse lighting significantly influences the growth period and seedling quality. For instance, in the case of tomatoes, lighting begins after the plant seedlings have grown two leaves, and 12 days of continuous lighting can reduce the seedling preparation period by 6-8 days. However, more than 24 hours of lighting can disrupt plant growth. The most suitable lighting time is 8 hours per day.

On cloudy and low-light days, artificial lighting is necessary. Providing crops with at least 8 hours of light at night, with a fixed lighting time every day, is essential. However, a lack of nighttime rest may disrupt plant growth and reduce yield.

For tomatoes, the most effective lighting time is from dusk to midnight, 16:00-24:00, or from midnight to early morning, 24:00-8:00, providing light for 8 hours and resting for 8 hours. Throughout the growth period, plants should receive light, from seedlings to transplanting. In the final stage, lighting should be reduced to 6 hours per day or even stopped for 2-3 days if the lighting conditions are poor, usually lasting for a month until transplanting.

Under fixed environmental conditions such as CO2, moisture, nutrients, temperature, and humidity, the photosynthetic photon flux density (PPFD) between the light saturation point and the light compensation point directly determines the relative growth rate of plants. Therefore, an efficient light source PPFD combination is key to the production efficiency of plant factories.

Choice of Light Source

A scientific choice of light source allows better control of plant growth speed and quality.

When using artificial light sources, it is essential to choose sources that closely match natural light conditions needed for plant photosynthesis.

Measuring the "Photosynthetic Photon Flux Density (PPFD)" of light sources affecting plants helps control the rate of photosynthesis and the efficiency of the light source. The quantity of photosynthetically active photons initiates the plant's photosynthesis: including light reactions and subsequent dark reactions.

Light sources should possess the following characteristics:

1. Efficiently convert electrical energy into radiant energy.

2. Achieve high radiation intensity within the effective range of photosynthesis, especially low infrared radiation (heat radiation).

3. The emitted light spectrum of the bulb should meet the physiological requirements of plants, particularly within the effective spectrum for photosynthesis.

Among various artificial light sources emitting intensities within the effective range of photosynthesis, sodium lamps have twice the energy conversion efficiency compared to mercury lamps. Sodium lamps are the most effective light sources for influencing photosynthesis and proper plant growth in greenhouses. Tubular sodium lamps can achieve high-efficiency radiation of 150lm/w, making them the most beneficial choice for the growth of various crops. Increasing the sodium vapor pressure in ceramic arc tubes can expand the spectrum of blue and red light, precisely what is sought for within a broader wavelength range.

Regarding the application of high-pressure sodium lamps in horticultural products, we recommend PLANTASTAR (OSRAM), SON-T AGRO (PHILIPS), and LUCALOX XO (GE). Their differences lie in offering a higher range of 0-40% blue light, stimulating plant chlorophyll. To obtain the highest radiant energy, all sodium lamps have reflector layers installed on the inner side of the lampshade. However, currently, most domestic factories often use sodium lamps intended for street lighting as plant-use sodium lamps, causing considerable losses to numerous users.

The light environment is an indispensable physical environmental factor for plant growth and development. By adjusting light quality, controlling plant form and structure becomes a crucial technology in facility cultivation.

The spectrum range's influence on plant physiology:

280nm ~ 315nm: Minimal effect on morphology and physiological processes.

315 nm~ 420nm: Low chlorophyll absorption, affecting photoperiodic effects, and inhibiting stem elongation.

420 nm~ 500nm (Blue): Maximum chlorophyll and carotenoid absorption, having the greatest impact on photosynthesis.

500 nm~ 620nm: Moderate pigment absorption rates.

620nm ~ 750nm (Red): High chlorophyll absorption, significantly impacting photosynthesis and photoperiodic effects.

750nm ~ 1000nm: Low absorption, stimulating cell elongation, influencing flowering and seed germination.

>1000nm: Converted into heat.

The rich variety of wavelengths precisely matches the spectrum range required for plant photosynthesis and photomorphogenesis. The narrow spectrum bandwidth can combine pure monochromatic light and composite spectra as needed, evenly irradiating crops with specific wavelengths. This not only regulates flowering and fruiting but also controls plant height and nutrient content. With low heat generation and minimal space occupation, it can be used in multi-layer cultivation systems, achieving low heat load and compact production spaces.

Sunlight is an essential factor for plant growth, besides nutrients and water. However, every grower knows that sunlight cannot be controlled. Hence, artificial sunlight is increasingly recognized in horticultural cultivation because it allows growers to control plant growth seasons and significantly shorten the plant's growth period.

Uses include:

1. As supplementary lighting, it can enhance illumination at any time during the day, consistently aiding plants in photosynthesis, especially during the winter months, extending effective lighting.

2. It can effectively and scientifically control the light required by plants regardless of dusk or night, unaffected by any environmental changes.

3. In greenhouses or plant laboratories, it can entirely replace natural light to promote plant growth.

For most growers, metal halide lamps and sodium lamps are the best light sources to replace natural sunlight. Metal halide lamps, rich in blue light, are suitable for initial plant shoot and leaf growth, while agricultural sodium lamps, rich in red-orange light, have a positive effect on promoting flowering and fruiting.

China's rapid development of facility horticulture has brought attention to lighting technology controlling plant growth environments. 

Facility horticulture lighting technology is primarily applied in two aspects:

1. As supplemental lighting for photosynthesis in conditions of low sunlight or short sunlight duration.

2. Induction lighting for plant photoperiod and photomorphogenesis.

3. Primary lighting for plant factories.