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Planting Tips for Facility Agriculture with LED Grow Lights

  Signify, formerly known as Philips Lighting, changed its name in 2018. Signify manufactures state-of-the-art professional lighting for consumers, specific industries and the Internet of Things, including LED grow lights designed for facility agriculture. Today, LEDs are being used on a growing scale in greenhouses, vegetables and flower crops.

  While many crops have been shown to grow under 100% LED lighting, growers sometimes opt for a mixed light solution as a first step. When a cultivation facility transitions to LED or a partial transition, significant energy savings can be achieved on the one hand, and light intensity can also be increased on the other. In addition to choosing the right LED spectrum, growers should also consider the cultivation setup in general to make the transition successful.

  Factors to consider here include planting density, irrigation, and plant variety, to name a few. Currently the most widely used LED modules have an efficiency of 3.2 to 3.7 µmol per joule of electrical input, while the efficiency of high-pressure sodium lamps is only 1.8 µmol/J, which is 40% to 50% lower. Aside from the energy saving factor, LEDs have the added benefit of allowing better control of the indoor climate, including temperature and light. Because high-pressure sodium lamps produce heat radiation when they work, LED lamps do not. Therefore, growers should always pay attention to understand the suitable climate and cultivation conditions for LEDs. While different cultivation methods vary widely, there are several common factors. In this article, Signify's vegetable crop expert Erik Stappers shares what his team has learned from the experience.

1. Optimize light intensity with LED grow lights with adjustable controls

  Obviously, the grower should choose an LED spectrum, and one that has been validated for a particular crop. For many crops, the industry has developed their corresponding spectra, which can be selected from a database of more than 150 validated spectra. When high pressure sodium lamps are replaced by LEDs, the total light intensity within a facility typically increases significantly. In this case, being able to adjust the control of LED intensity is useful: with adjustable units, growers can respond to crop, weather conditions and energy demands without compromising on the uniformity of light. Another benefit of dimmable LEDs is that they are approximately 10% more efficient when dimmed, reducing energy consumption per lighting unit.

2. Crop physiological activity is the key

  Allowing crops to absorb all the light and neglecting to create the right environment for them to grow is a common mistake in facility farming. The assimilates produced by photosynthesis should be distributed by plants to where we want them to go, usually fruits and flowers. If proper measures are not taken, crop transpiration may be too low, keeping plant temperatures too low, or causing insufficient uptake of fertilizer nutrients.

  During cultivation with LED grow lights, since there is no heat radiation, growers will use barriers or close windows to keep the heat in the facility. This can lead to an overly passive indoor climate, which can cause problems with the transpiration of crops. There are a few options for improving your plant's activity, but the key is to drain the fluid around the plant. For example, consider using a fan to bring air flow, or adding a small heating pipe to the screen, or leaving the window slightly open. Also, the combination of active dehumidification and LEDs is also a perfect choice.

  In many cases, the energy cost savings from LED lighting can be partially invested in the heat input within the facility. The additional heat input required for different crops varies widely; however, the net energy cost savings with increased heat input compared to high pressure sodium lamps is still considerable. In fact, heating also costs less than electricity consumption in most cases.

3. Pay attention to plant status

  For optimal growth, plants should always be the focus of attention. Plants will eventually show the degree to which they convert the light provided into growth and development, so growers should pay close attention to crop water absorption, growth rate, etc., and adjust the climate accordingly to maintain crop balance. For many crops, growers need more control over their plants under LED grow lights in order for them to use photosynthesis in the right way. For example, consider water balance, pruning strategies, and adjust soluble salt concentrations or nutritional formulas if needed, among other things.

  For crops, a 20-degree high-pressure sodium lamp greenhouse feels very different from a 20-degree LED greenhouse. This means that when using LED grow lights, growers should look more at the plant temperature than the surrounding temperature. Also, it's a good idea to look at the temperature of each part of the plant individually. For example, the roots and fruit of a plant are affected differently by temperature than the top of a plant. An example of this is that in hanging wire cultivation, growing pipes are used more with LED or mixed lighting to directly affect the temperature of the fruit.

4. Barriers control plant temperature

  In many cases, growers with temperature-controlled barriers next to shading barriers are more flexible and have better control of moisture and plant temperature than growers with only shading barriers. Using temperature-controlled barriers to control plant temperature has great advantages, especially for growers who are used to high-intensity HPS lighting. In the case of low or even negative outside temperature, they do not realize the influence of thermal radiation generated by lamps. In the case of LED lighting, it may be a good option to turn off the temperature-controlled barrier completely; this will limit the amount of heat the crop emits to the atmosphere, while air exchange and dehumidification can continue.

5. Cultivation according to the amount of light

  When higher light intensities are applied, the luminaires themselves only limit and affect planting to a lesser extent. Especially in winter, artificial lighting will bring a steady amount of light. Therefore, calculating the amount of available light can create a stable cultivation environment to ensure the continuity of light. Especially when heat and amount of light can be controlled separately with LED lighting, lighting is no longer a bottleneck. As a grower, you should still be aware that a certain amount of light is required for crop growth and production potential; otherwise, the plant is overloaded and becomes unbalanced, making it difficult to recover in winter. Therefore, it is critical to determine planting density, harvest weight, harvest stage and pruning strategy based on realistic light levels.

  More and more growers are turning to LED grow light lighting, convinced of its possibilities. Maximizing LED potential requires understanding your crop to the fullest; consider not only the light, but all the growing factors in the greenhouse, and let the plants guide your decisions.