Greenhouse lighting system and which green lightings fit your needs

Supplement lighting greenhouse

 Smart greenhouses are the future of farming

Over the next 30 years, the world’s population is predicted to grow by up to 34% and urbanization will increase by around 20%. To feed this wealthier and larger population, food production must increase by an estimated 70%

Plants are the only organisms capable of the amazing feat called photosynthesis, by which carbon dioxide and water are converted into carbohydrates using light. Light from the sun or other sources runs the greenhouse. The greenhouse should provide a space with optimal conditions (light, temperature, nutrition, pest control, etc.) for the plants so that they can perform photosynthesis. 

The greenhouse should provide a space with optimal conditions (light, temperature, nutrition, pest control, etc.) for the plants so that they can perform photosynthesis. 

About supplement in the greenhouse, there is something you have to know.

How does it work with supplement lights and grow of crops?

One of the key factors in optimum plant growth is providing adequate light for photosynthesis. The leaf is designed to absorb nearly 95% of wavelengths between 400 – 700 nm, but only 5% of the 700-850 nm waveband is absorbed. Of the remaining 95% of the 700-850 nm waveband, 45% is reflected, and 45% is transmitted. Numerous greenhouse equipment is blocking the light from reaching the plant inside as well.

In conclusion, a large portion of the solar radiation ( between 30 -50%) does not reach plants. The greenhouse cover, plastic or glass, will also have an important impact on light transmission. Therefore, supplement lights are necessary for crops.

Three parameters of grow light used in greenhouse industries are relevant: quality, quantity, and duration. All three parameters have different effects on plant performance: 

Light quantity (intensity): Light quantity or intensity is the main parameter which affects photosynthesis, a photochemical reaction within the chloroplasts of plant cells in which light energy is used to convert atmospheric CO2 into carbohydrate. 

Light quality (spectral distribution): Light quality refers to the spectral distribution of the radiation, i.e. which portion of the emission is in the blue, green, red, or other visible or invisible wavelength regions. For photosynthesis, plants respond strongest to red and blue light. The light spectral distribution also affects plant shape, development, and flowering (photomorphogenesis). 

Light duration (photoperiod): Photoperiod mainly affects flowering. Flowering time in plants can be controlled by regulating the photoperiod.

Concepts you should know:

DLI—-The Daily Light Integral (DLI) was developed by scientists to provide a measure of cumulative photosynthetically active radiation (PAR) received by plants over the day. The concept is similar to totaling daily rainfall measured in inches per day.

It integrates light intensity in micromoles per square meter per second (μmol/sqm/s) and totals this over 24 hours. The total daily integral is expressed as moles per square meter per day (mols/sqm/day).

Total daily light requirements vary considerably between different plant species. If the measured DLI is less than what is recommended, supplemental light could be supplied to make up the difference.

Plant physiology

Plants grow by converting photons (sunshine or supplemental lighting), water, and CO2 to sugars and oxygen. The environmental conditions and physiology of each plant determine the rate of photosynthesis. In the light reactions of photosynthesis, photons are absorbed by photosynthetic pigments, and the energy is used to transport electrons. This electron transport then results in the production of chemicals required for the synthesis of sugars. The electron transport rate (ETR) is a direct measure of the light reactions of photosynthesis in response to photosynthetic photon flux (PPF) ETR is the driving force for photosynthesis and ultimately crop growth.

How to increase DLI to get harvest yields?

Because increasing DLI is an effective way to increase yields. Therefore, either by giving plants more intense light, or giving them more hours of light a day may drive plants to produce more. However, excessive light can harm yields and waste energy, growers need to based on the crops to decide how much hours they use their supplement lights and how much PPFD the supplement lights provide. 

To get this result, growers need to know that the DLI outdoors varies depending on latitude, the time of year, and the amount of cloud cover. When the DLI is low it would be wise for growers to maximize the amount of natural light that can reach the crop.

Greenhouse structures are an obstacle for solar radiation: frames, glazing bars, dirt, gutters, because they are opaque, absorb, or reflect all the light that reaches them. During the summer, with long days and high sun angles, this is not a problem; however, during the fall, winter and spring, light levels are usually marginal. Throughout the year, outdoor DLI ranges from 5 to 60 mol/m2/day, however, in the greenhouse, values seldom exceed 25 mol·/m2/day. Add to this the loss of light due to greenhouse glazing and the obstructions in the greenhouse and the light that gets to plants is usually less than is needed for optimum plant growth.

Essentially, low levels of lighting for long periods are more energy-efficient than high levels for short periods. Furthermore, supplemental light provided when sunlight levels are low will be used more efficiently than supplemental light provided when sunlight levels are high.

The formula for calculating DLI is: μmol m-2s-1 (or PPFD) x (3600 x photoperiod) / 1,000,000 = DLI (or moles/m2/day)

PPFD is the number of photons that arrive at a specific area (m2) every second, measured in micromoles (µmol m-2 s-1)

1.000.000 micromoles = 1 mole

3600 seconds = 1 hour

For example, if you know tomato needs 30 DLI per day, normal sunlight provides 20 DLI per day. You need 10 more DLI. You want to use supplement light for 18 hours for tomato, so what kind of PPFD you need to consider for the supplement light?

PPFD=(10*1,000,000)/(3600*18)=154.32

If you want to hang the lights above crops 80cm distance, you need to look for a grow light which has PPFD value of 154.32 µmol m-2 s-1 @80cm 

The relationship between the light quantity of greenhouse and yield

 

Vegetable grow with LED Light

There are many aspects attributed to yield increase, such as higher temperature, solar radiation, adapt plant density, CO2 concentration, temperature, and leaf area index. Among them, solar radiation regards as one of the important factors which largely influence the growth of crops. The radiation crops receive to determine the yield result. That explains that more and more growers concern about using grow lights to improve the harvest yield of grown crops.

The Netherlands is one of the frontier countries apply supplement light in the greenhouse. In the last 30 years, the Dutch growers have usually taken a 1% additional light results in 1% additional growth and production. According to their experience, by lettuce, cucumber, rose, freesia, poinsettia, and Ficus, it is important to have high light levels during their growing process. All growers are convinced that the relative effect of light is larger in winter than in summer.

To test the  1% additional light results in 1% additional growth and production principlethe scientists choose soil-grown vegetables, fruit vegetables, cut flowers, and bulb flowers to test quantification of the growth response to the light quantity of greenhouse Grown Crops.

Soil grown Vegetables (Lettuce, Radish)

For soil grow vegetables by increasing 1% radiation leads to 0.6% to 1.4% increase in the yield. The formation of radish tubers is strongly dependent on light. The effects of light have more influence on tuber weight than on sprout weight, and consequently, the shoot/tuber ratio increases at low light. In the final stage of tuber development has a stronger effect on the final tuber weight than light during the initial phase of the crop. However, when a lack of light, a 1% decrease in radiation leads to a reduction in both the fresh and dry weight of lettuce heads by about 0.8%.  

Fruit Vegetables (Cucumber, Tomato, Sweet Pepper)

Green LEDs with high PPF (300 µmol/m-2/S-1) are most effective to enhance the growth of lettuce. Supplementation of green light enhanced lettuce growth under red and blue LED illumination.

When reducing light during the growth of cucumber, it will change in dry matter partitioning and water content, hence, the light reduction has a stronger effect on cucumber yield than duration during a short period. The reduction in cucumber yield due to 1% less radiation varied in most cases between 0.6 and 1.2%. Pepper is slightly more sensitive to light than are tomato and cucumber, since when reduce 1% light, reducing the yield of tomato between 0.6 and 1.1% and 0.8 and 1.3% sweet pepper. For fruit vegetables in general, a 1% light reduction leads to an average yield reduction in the range of 0.8 to 1%.

Cut Flowers (Rose, Chrysanthemum)

LEDs can play a key role in floriculture by providing a suitable light spectrum (quality and duration). Light controls the circadian rhythm of plants which means the clocking of plants to day (light) and night (dark) cycles, and this circadian rhythm influences photomorphogenesis.

Red and far-red light have been shown to affect photomorphogenesis, thus, the ratio of red and far-red light plays an important role in the regulation of flowering. Flowering in plants is mainly regulated by phytochromes (a group of plant pigments), which occur in two forms: Pr (responds to red light) and Pfr (responds to far-red light). These two pigments (Pr and Pfr) convert back and forth. Pr is converted into Pfr under red light illumination and Pfr into Pr with far-red light. 

The active form which triggers flowering is Pfr. Pr is produced naturally in the plant. The ratio of Pr to Pfr is in equilibrium when the plant receives light (day) because Pr is converted into Pfr by red light and Pfr is converted back to Pr by far-red light. Back conversion of Pfr is however also possible in a dark reaction, so it is the night (dark) period which mainly affects the ratio of Pr to Pfr and controls the flowering time in plants

In terms of cut flowers such as rose, whether flowers can get enough light affects quality effects. Similar to soil grow vegetables a reduction of 1% light reduced yield between 0.4 and 1.2%. A decrease in radiation results in fewer shoots, lower shoot weights, and less quality in rose. Moreover, when flower buds receive not enough light, it can cause blind shoots. In winter, lack of light have a great influence on flowers. In chrysanthemum, the effects of a 1% reduction in radiation led to yield reductions varying between 0.3 and 1.0%, but in most cases, a yield reduction of 0.6% fitted reasonably with the observations. 

Bulb Flowers (Freesia, Lily)

For several long-day plants, the addition of far-red light (700-800 nm) to red light (600-700 nm) extend the day length promotes flowering and growth. The higher energy efficiency and longer lifetime are the most important advantages of LEDs in floriculture.

When reducing 1% light, it decreases around 0.5% fresh weight of shoots and till 1.2%. These data were based on summer experiments. In winter the effects of light are likely to be stronger.

In conclusion, a 1% light increment results in 0.5 to 1% increase in the harvestable product can apply to most of the crops. As a rule of the thumb, the following values may be used: 0.8-1% for soil-grown vegetables, 0.7-1% for fruit vegetables, 0.6-1% for cut flowers, 0.25-1.25 for bulb flowers, 0.5-1% for flowering pot plants and 0.65% for non-flowering pot plants. These are average values.

How does light affect plant growth? Different spectrum affects the growth of crops.

Plants require light throughout their whole life-span from germination to flower and seed production. During the grow process, they do not absorb all wavelengths of light (solar radiation), but selective in absorbing the proper wavelength according to their requirements. 

Chlorophylls (chlorophyll a and b) play an important role in the photosynthesis but they are not the only chromophores. Plants have other photosynthetic pigments, known as antenna pigments (such as the carotenoids β-carotene, zeaxanthin, lycopene and lutein etc.), which participate in light absorption and play a significant role in photosynthesis.

LED is a type of semiconductor diode which allows the control of spectral composition and the adaptation of light intensity to be matched to the plant photoreceptors in order to furnish better growth and to influence plant morphology as well as different physiological processes such as flowering and photosynthetic efficiency. Several reports have confirmed successful growth of plants under LED illumination. 

For example, biomass yield of lettuce increased when the wavelength of red LED emitted light increased from 660 to 690 nm. Blue LEDs (440 and 476 nm) used in combination with red LEDs caused higher chlorophyll ratio in Chinese cabbage plants. Positive effects of blue (400-500 nm) LED light in combination with red LED light on green vegetable growth and nutritional value have been shown in several experiments. Red LED (640 nm) light as a sole source and results showed increase in anthocyanin contents in red leaf cabbage. Green (495-566nm) and yellow (566-589nm) light contributes to photosynthesis, orange (589-627 nm) will optimize for maximum photosynthesis and red light (627-770 nm) enhances flowering, stem elongation. Several horticultural experiments with potato, radish and lettuce have shown the requirement of blue (400-500 nm) light for higher biomass and leaf area. 

The most important part of the light spectrum is 400 to 700 nm which is known as photosynthetically active radiation (PAR), this spectral range corresponds to more or less the visible spectrum of the human eye. 

Far-red also important during the growing process. Application of far-red (730 nm) with red (640 nm) caused increase in total biomass and leaf length while anthocyanin and antioxidant potential was suppressed. Addition of far-red (735 nm) to the red (660 nm) LED light on sweet pepper resulted in taller plants with higher stem biomass than red LEDs alone . 

Solar radiation

The solar radiation can be divided into three wavebands:

  • the ultra -violet (UV) corresponds to the wavelengths less than 400 nm and can cause skin damage because of their high energy.

  • the visible light, within the 380-770 nm waveband, and contains the PAR (400-700 nm) waveband. The different colors of the visible light, which corresponds to different waveband, may not have the same function towards plant’s development. 

  • the infrared (IR), greater than 770 nm and have an heating effect. Red: Far-red (R:FR) ratio is very important for plants because it influences plant growth response.

Red
Red (630-720 nm) light is required for the development of the photosynthetic apparatus and photosynthesis. It is essential for the growth of stems, as well as the expansion of leaves. This wavelength also regulates flowering, dormancy periods, and seed germination.

Blue
Blue (400-520 nm) light is important for the synthesis of chlorophyll, chloroplast development, stomatal opening and photomorphogenesis. Blue light needs to be carefully mixed with light in other spectra since overexposure to light in this wavelength may stunt the growth of certain plant species. Light in the blue range also affects the chlorophyll content present in the plant as well as leaf thickness.

Green
Green (500 – 600 nm) penetrates through thick top canopies to support the leaves in the lower canopy. Green light alone is not enough to support the growth of plants because it is least absorbed by the plant but when used in combination with red, blue, and far-red, green light will certainly show some important physiological effects. Supplementation of green light enhanced lettuce growth under red and blue LED illumination. Green LEDs with high PPF (300 µmol/m-2/S-1) are most effective to enhance the growth of lettuce.

Far-red LED light
Far-red LED light (700-725 nm) which is beyond the PAR has been shown to support the plant growth and photosynthesis . Far Red Light also passes through dense upper canopies to support the growth of leaves located lower on the plants. In addition, exposure to IR light reduces the time a plant needs to flower. Another benefit of far red light is that plants exposed to this wavelength tend to produce larger leaves than those not exposed to light in this spectrum.

Red+Blue
Different wavelengths of red (660, 670, 680 and 690 nm) and blue (430, 440, 460 and 475 nm) light might have uneven effects on plants depending on plant species.

Green + Red+ Blue
The effect of green (525 nm) LED light on germination of Arabidopsis seedlings and results showed that seedlings grown under green, red and blue LED light are longer than those grown under red (630 nm) and blue (470 nm) alone.

Green+Red+Blue+Far-red
Red and far-red light have been shown to affect photomorphogenesis, thus, the ratio of red and far-red light also plays an important role in regulation of flowering. Experiments with different wavelength of green, red, blue, and far-red lights (provided by LEDs) would be beneficial in determining the species specific optimal wavelength for plant growth. The findings of the light response spectrum studies could be used to design an energy efficient tailored light response spectrum for specific plant species.

As plants mature and go through their growth cycle from seedling, to adult, and then flowering and fruiting they use different color spectrums so the ideal LED light is different for each stage of growth. The best color spectrum also depends on the type of plant you are trying to grow. This can get very complicated and is important for commercial growers where they want to maximize results.

It also suggest that lights can increase nutritional value and enhanced antioxidant status in green vegetables: increased carotenoid, vitamin C, anthocyanin and polyphenol. In future more and more research will help us to better understand how lights shape growth of plant.