The application of LED supplemental lighting in greenhouse vegetables and flowers is becoming more and more popular. Although it has been confirmed that many crops grow well under full LEDs, but sometimes growers prefer blendedlighting schemes (switching between LED supplemental lighting and other lighting technologies such as HPS). When all or part of the supplemental lighting is converted to LED, energy consumption can be significantly saved or light intensity can be increased. In either case, after selecting an appropriate LED lighting solution, the overall cultivation plan should be kept in mind to ensure successful conversion. This includes factors such as plant planting density, irrigation and varieties. HPS lamps produce radiation heat, while LEDs generally produce very little radiation heat. The light efficiency of the most widely used LED module on the market is 3.2-3.7μmol/J, and the light efficiency of HPS is 1.8μmol/J, which is 40%-50% lower. In addition to energy efficiency, there is a big difference between HPS and LED, LED can better control the climate by independently controlling temperature and lighting. As a grower, you should always be aware of the application of LED supplementing light to create suitable climate and cultivation conditions. Of course, different cultivation methods have great differences, but there are also some common points.
1. Optimize illumination with dimmable LEDs When HPS are replaced by LEDs, the overall level of illumination in the greenhouse usually increases significantly. In this case, dimming the LED intensity is very useful: with a dimmable device, you can adjust the intensity without changing the uniformity of the illumination, depending on the crop, weather conditions, and energy market demand. Another advantage of dimmable LED is that when it is dimmed, the light efficiency increases by about 10%, which can reduce energy consumption.
2. Crop vitality is the key Photosynthetic assimilate partitioning is an important consideration. It is a misconception to try and artificially supplement light in order to get the plant to absorb and utilize all light, without creating an environment suitable for the plant. We should take measures to direct the assimilates to the parts of the plant we want them to go, usually the fruits and/or flowers. Without proper measures, crops may suffer from too little transpiration, low temperatures, or inadequate nutrient uptake. In some applications of LED cultivation, the insulation curtain is used more frequently, and the vent window is often closed to maintain the heat in the greenhouse. This may lead to an overly passive climate environment, which affects the plant's transpiration. There are several ways to maintain the vitality of plants. The key lies in the flow of air around the plants. You can consider using fans, or maintaining a minimum heating temperature and combining with an incompletely closed insulation curtain, or slightly opening the window to promote air flow. Other management methods, such as active dehumidification through air handling units, are also perfect control operations when applying LED. In this way, you can actively maintain heat and dehumidify with limited energy consumption. In some cases, we found that the electricity savings from LED were slightly offset by the additional heating required to compensate for greenhouse temperature. There is a great variation in how much additional heating different crops require, but compared to HPS, the net savings are still quite considerable. Furthermore, in most cases, the cost of heating is lower than the cost of electricity.
3. The plant growth law For optimal growth, the growth law of the plant itself should always be in the most important position. The crop will eventually show what kind of light level is needed to achieve the desired growth and development state. Pay attention to observe the indicators such as water absorption and development speed, and adjust the climate accordingly to maintain the balance of the crop. For many crops, in order to make the plants use the assimilates produced in the right way compared with HPS, you need to make the reproductive growth of plants more vigorous. For example, consider implementing larger DIF, water balance, (leaf) removal strategies, and adjust EC or nutrient formulation when needed. For your crops, there is a big difference between the greenhouse temperature under 20℃ of HPS and LED. This means that when using LED, you should pay more attention to the temperature of plants rather than the environment. It is also a good idea to observe the temperature of each part of the plant separately. For example, when using different heat sources, the temperature of roots and fruits will be affected differently compared to the top of the plant. Another example in this regard is that in high rack crops, heating pipes are used more with LED or mixed lighting to directly affect the temperature of the fruits.
4. Using thermal screens to control plant temperature In many cases, we discover that thermal screens combined with shading curtains are more flexible and provide more control over humidity and plant temperature than thermal screens alone. Using thermal screens to control plant temperature has many advantages. Especially for those growers accustomed to using high intensity HPS, they often do not realize the effect of heat radiation from the lights when net radiation is low or even negative. In many cases, closing thermal screens almost completely is a good option to reduce the crop's heat radiation loss while still allowing for air exchange and dehumidification.
5. Always calculate based on total amount of light As the intensity of light increases, the possibility of light becoming a limiting factor for cultivation will gradually decrease. In winter, artificial lighting can bring stable light. Therefore, it is possible to create a stable cultivation by using the total amount of light to ensure continuity. Especially when the temperature and light can be controlled separately with LED, light will no longer be a bottleneck. But as a grower, you should be aware of the total amount of light to be achieved and the growth or production potential arising from it. As it is recognized that if the plant load is too high, the crop growth balance will be broken and it will be difficult to recover in winter, it is necessary to have a clear understanding of planting density, harvest yield, harvest stage and leaf removal strategies.