High-pressure lamps (HID) have been used in horticulture for more than half a century. Although recent light emitting diodes (LED) technology is more efficient, HID lamps have come a long way in all these years. HID lamps, especially HPS lamps, are still the most widely used in technical horticulture, although the great advantages of a higher energy efficiency and a tailored light spectrum make LED technology the best option for cultivators.
Nowadays, advanced systems for indoor horticulture use LED technology for improving crop growth, enhancing the plant productivity and favouring the best nutritional quality formation. In closed environments, as indoor growing modules, the lighting system represents the only source of light and its features are fundamental for obtaining the best lighting performances for plant and the most efficient solution. LED lighting engines are more efficient compared to the lighting sources used traditionally in horticulture and allow light spectrum and intensity modulations to enhance the light use efficiency for plants.
The importance of good lighting for indoor cultivation
Photons are simultaneously an energy source for plant growth and a signal for development. Through photosynthesis, plants convert photon energy into chemical energy powering life on the Earth. To maximize survival, plants need to find ways to efficiently capture photons. Light plays a very important role acting as the trigger of the photosynthetic chemical reaction. The higher the light intensity, the more nutrition and carbon dioxide in the air the plant needs.
In order to get the maximum yield from a crop, adequate lighting as well as an adecquate contol of the other cultivation variables are required. A properly designed artificial lighting system and light plan adds great value to the production, allowing the chosen crop to be grown all year round.
Appropiate horticulture lighting requires to consider three important aspects:
Light intensity refers to the quantity of photons falling in the canopy of the crop. Depending on the type of crop, the grow lights need to emmit the right light intensity to suit the needs of the plant and the growing area. The requirements between crops may vary significantly, even between varieties of the same species. The accumulated photons obtained from a certain light intensity during a day is called DLI (Daily Light Integral).
The photoperiod, or day length, is the number of consecutive hours of light in a 24-hour period. The number of hours of darkness — not the photoperiod itself — is what influences photoperiodic plant responses. In the case of photodependent plants, depending on the number of hours of light of the appropiate intensity, the phases of the crop will be controlled and managed from the vegetative to the flowering stage.
Light is a form of electromagnetic radiation, a type of energy that travels in waves. Together, all the types of electromagnetic radiation make up the electromagnetic spectrum. The light from a specific portion of the spectrum emitted by grow lights can be different and ir presents a variety of colours depending on the type of electromagntic radiation emitted. The colours of the light spectrum affect the morphology and chemical compounds of crops, such as the secondary metabolites. which are important for the organoleptic properties of the crop and therefore the final product after harvesting. Choosing an appropiate light spectrum for the different stages of the plant favours the production and quality of the final product.
How to light our growing space?
The distribution of the lighting equipment in the growing spaces is a critical point in order to obtain the maximum yield of the harvest. These growing spaces must be homogeneously illuminated in order to obtaing an uniform growth, avoiding that some plants receive more light than others. Cultivators need to analyze their facility and consider that the higher the lighting equipment, the greater the homogeneity and the lower the intensity. On the contrary, if we bring the lamps very close to the plants we will obtain a high intensity but there will be less homogeneity, thus the plants will not receive the same intensity equally, obtaining an uneven growth in the cultivation area.
How much light does your grow room need?
It is important to note that in agronomy, light intensity reaching the plants, or Photoshynthetic Photon Flux Density (PPFD), is measured in micromoles per second per square metre µmol/s/m².
The amount of PPFD indicates the amount of µmol that a surface of 1 square metre receives every second.
The required intensity is different depending on the crop needs.
- Tomato: 150 – 360 µmol/s/m²
- Cucumber: 115 – 355 µmol/s/m²
- Pepper: 115 – 325 µmol/s/m²
- Roses: 165 – 355 µmol/s/m²
- Chrysanthemum: 100 – 225 µmol/s/m²
- Strawberry: 65 – 145 µmol/s/m²
- Medicinal Cannabis in Vegetative Process: 275 – 575 µmol/s/m²
- Medicinal Cannabis in Flowering process: 600 – 1000 µmol/s/m²
The number of grow lights needed for every crop will depend on the surface area and the type of grow light used, as well as the target harvest yield.
Light during growth and flowering in indoor cultivation
The vegetative or growing process in plants with short photoperiods occurs when the plant receives more hours of light per day than during the flowering process. As the number of hours is greater, the intensity of light can be lower, hence the lighting equipment used in cultivation allows the intensity to be regulated, so that it can be adapted to the plant’s phases. The flowering or fruiting process of plants with short photoperiods occurs when the number of hours of light is less than during the vegetative process. The photosynthetic process is more demanding and the number of hours of light is lower. Therefore, the intensity requirements are higher in this process.
Types of HID lamps for indoor cultivation
HID lamps can be classified by their technology or by their connection.
– HPS. High pressure sodium. They are the most widely used and offer greater intensity with lower energy consumption, they are more efficient. They enhance the flowering processes due to their greater amount of reds.
– MH. Metal halide. They are less energy efficient. They are used in seed germination and vegetative processes as they provide a greater quantity of blue.
– CMH. Ceramic metal halide. This is the most recent technology, and although it does not reach the energy efficiency of HPS, it does have a balanced spectrum between blues and reds, being suitable for full cycle crops.
– DE. Double Ended. These are double ended lamps that use the K12X30s lampholder. Usually used for 1000W lamps that are installed in luminaires.
– E40. These are lamps with a threaded socket. Typically used for 600W lamp.
– PGZX18. Usually used in 315W CMH lamps.
How to choose the best lighting for a crop
Not all growers have the same crop management, nor do they all have the same demands. This conditions the level of economic investment allocated to each project. Fortunately, there are several technological solutions, with different levels of investment. So there are several options to choose from. Generally speaking, making the right choice for the best lighting involves choosing equipments with a high electric efficacy (µmol/J), both in terms of energy and product design. Electric efficacy is a measure the of light intensity given emitted by a grow light in relation to the energy consumption to emmit it. Nowadays, the best full spectrum LED grow lights present approximately around 2.7 µmol/J. In relation to HID technology, 1000W luminaires and Double Ended lamps are the best alternative, as they combine all these features with a moderate level of investment, although the best lamps only reach 2.1 µmol/J (just the lamp, without the equipment, meaning that the real efficacy would be even lower).
The best lamps for indoor growing will depend on the area, the plant and the harvesting objective. In small growing areas and with low production requirements, CMH is more suitable than HPS, although it is less energy efficient. Nevertheless CMH offers a better spectrum of light that helps to obtain a higher quality. In large growing areas, where productivity and energy consumption are the most important parameters, choosing lighting systems that incorporate high efficacy equipments is the right solution.
Since last few years, LED lighting equipments have achieved superior results with lower energy consumption than HID, but it needs a higher level of initial investment. Nevertheless, the energy consumption savings with LEDs are really important and interesting to consider for the ROI (Return of Investment) in the long-term.
Tips and rules for placing the lights for our crops
- Consider the maximum power of your electrical supply point. If necessary, ask your supplier for advice.
- Plan your growing area correctly, without having excessive spaces between plants, lighting an empty corridor costs money.
- Install the lamps at the correct height depending on their anchorage points, the area and the type of crop.
- Choose the right wattage and type of equipment to optimize grow light efficacy.
- Always choose the most energy efficient lighting systems.