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Greenhouse lighting system and which green lightings fit your needs

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 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 

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