- What is the photoperiod phenomenon of plants?
- What kind of light does the photosynthesis of cannabis absorb?
- Do you know the concept of grow light parameters?
- What are the grow lights for cannabis cultivation? Their strengths and weaknesses?
What is the photoperiod phenomenon of plants?
Before we officially start, we must first understand a term, photoperiod phenomenon. The photoperiod phenomenon refers to the reaction of organisms to changes in the light cycle and dark cycle. The most significant effect of photoperiod on organisms is to start reproduction or delay reproduction. Long daylight will cause many animals in cold regions to start breeding, such as hares and ferrets. Short days will allow many animals living in warm areas to start breeding, such as sheep and cattle. However, many animals are not very sensitive to changes in the photoperiod. Most of these animals have stable growth environments, such as people and animals around them.
Plants also have photoperiod phenomena. Compared with animals, plants behave more clearly. There are 6 specific manifestations, and we mainly talk about 3 common ones.
- Long-day plant (LDP)
It refers to the plants that can form flowers when the sunshine length is longer than a certain number of hours in the 24-hour day and night cycle. Extending the light to these plants can promote early flowering, on the contrary, prolonging the darkness will cause delayed flowering or failure to form flowers.
The long-day plants are: wheat, barley, rye, rape, spinach, radish, cabbage, cabbage, celery, beet, carrot, coneflower, camellia, rhododendron, osmanthus, hydrangea, etc. The typical long-day plant Hydrangea vulgaris must meet a certain number of days of 8.5 to 11.5 hours of sunshine to bloom. If the length of sunshine is shorter than 8.5 hours, it cannot bloom.
- Short-day plant (SDP)
It refers to the plants that can form flowers when the sunshine length is shorter than a certain number of hours in the 24-hour day and night cycle. Prolonging the darkness or shortening the light for these plants can promote early flowering. On the contrary, prolonging the sunlight will delay flowering or fail to form flowers.
The short-day plants are: rice, corn, soybean, sorghum, cocklebur, perilla, hemp, jute, strawberry, tobacco, chrysanthemum, begonia, winter plum, Japanese morning glory, etc. For example, chrysanthemums must meet less than 10 hours of sunshine to bloom.
- Day-neutral plant (DNP)
The flowering of this kind of plants is not sensitive to the length of sunlight, as long as other conditions are met, they can bloom under any length of sunlight. Such as rose, cucumber, eggplant, tomato, pepper, kidney bean, clivia, sunflower, dandelion, etc.
The above are the typical photoperiod characteristics. In order to make the short-day cannabis plant bloom, we must give it less than 15 hours of light per day, otherwise the cannabis will not bloom and stay in the growth period. We can also shorten the light in advance to stimulate the flowering of cannabis, so that the flowers enter the mature period in advance, so that we can harvest faster. By shortening the light time, we are sending a signal to the cannabis that autumn is coming. Growers now generally believe that 12 hours of light and 12 hours of darkness are the most conducive to cannabis blooming. However, there are also day-neutral marijuana on the market. The flowering node of this marijuana is not determined by the change of the photoperiod, but by the time of growth. When grown for enough time, this marijuana can bloom even in an environment without light, regardless of whether there is a change in light. This hemp is called self-flowering hemp.
In addition to affecting the reproduction time of plants, light is another very important plant activity-a necessary condition for photosynthesis. The pigments chlorophyll a, chlorophyll b, carotene, and lutein in plants absorb light to synthesize compounds such as sugar, oil, and protein. Photosynthesis is the process by which plants convert inorganic substances in their bodies into organic substances by absorbing the energy in light.
Let me first clarify a few misunderstandings or doubts that many people have.
What kind of light does the photosynthesis of cannabis absorb?
Cannabis absorbs all light throughout the growth period, but the amount of absorption varies for different parts and different growth periods. The figure below shows the light absorption spectrum of the whole cannabis.
The ordinate of this graph is the relative light intensity, which is a proportional value. 1 is the ratio of normal sunlight. The ordinate is the color of light corresponding to the wavelength of different light. The white light we usually see is the color of the fusion of various colors. The white light is composed of many different colors of light, and the sun is also the same. But plants selectively absorb white light. This picture shows us what kind of light hemp absorbs and what is the ratio of absorption.
During the growth period of plants, it is mainly the chlorophyll in the plant that is working. The light absorbed by the plant is mainly light with a wavelength of 380nm ~ 550nm, namely blue and green light, which is mainly used to grow new plant tissues and expand their body size. .
So why does hemp look green? The color reflected by an object is the color it represents. Isn’t that common sense?
This is because, as we can see from the above picture, the light absorbed by hemp at the wavelength of 450nm ~ 550nm is relatively small, that is to say, most of this part of the light is reflected by the hemp and not absorbed. The reflected light merges into the color of marijuana, that is, the exterior color of marijuana.
After hemp enters the pre-flowering period, hemp will begin to absorb a large amount of light with wavelengths of 550nm to 700nm, namely yellow light, red light, and deep red light. The greater the wavelength, the greater the energy of the light, and the plants after the pre-flowering period begin to absorb more energy for the production of various active substances. Male flowers absorb energy to make the pollen more active; female flowers absorb energy to make the calyx easier to fertilize, and also begin to secrete large amounts of cannabinoids to drive away foraging animals. From the spectrum chart, we can see that the light with a wavelength of about 650nm is relatively reflected, which is why female cannabis will appear reddish brown after the pre-flowering period.
Of course, this cannabis absorption spectrum does not represent all varieties of cannabis. There are also purple varieties of cannabis. Her absorption spectrum is different. She reflects blue and red light more during the flowering period, and then shows purple. Externally, it absorbs more light from 450nm to 600nm.
Therefore, when purchasing a grow light, we must first consider the light time. Lights that cannot be operated for a long time are totally unacceptable. On the other hand, we have to consider the light absorbed by the cannabis. The light we provide must be able to give the cannabis plant the light of the required wavelength. It must have the blue and green light required during the growth period, and must have the necessary after the pre-flowering period. We must use together or not consider the light color of yellow, red, deep red light, the light color is too single or the wavelength is not suitable. In addition, for energy-saving considerations, we need to make the lamp emit less light with a wavelength of about 500nm to reduce the waste of light color. And let the light intensity ratio match the ratio in the figure above, that is, more blue light and yellow-red light, relatively less light of 500nm wavelength and 650nm wavelength, to reduce the waste of light intensity.
After understanding the above knowledge, there will be a clear framework when choosing grow lights. But after understanding the plants, we still have to understand what different lights can provide, the advantages and disadvantages between them, and whether they are suitable for our plants.
Light is to plants as rice is to us. Plants produce glucose through photosynthesis for growth. In the previous section of this chapter, we shared what we eat with cannabis. Today we will talk about how much we eat and what bowl to use.
Do you know the concept of grow light parameters?
The professional term for how much cannabis eats is called illuminance, which refers to the amount of light radiation (luminous flux) received per unit area on the surface of an object that is uniformly illuminated, in Lux or lx. In order to allow marijuana to photosynthesize smoothly, we need to control the illuminance between 35000lux and 85000lux. Each plant growth lamp will identify its own luminous quantity, but this quantity refers to the luminous quantity at full load and zero distance. Light is a kind of electromagnetic wave, which will be greatly attenuated during the propagation, so as the distance increases, Some changes in external conditions such as temperature changes and air humidity changes, although under the same light, the illuminance at different locations and at different levels is different. Plants are affected by light, and the intensity of respiration and photosynthesis are also different. In order to maintain the most basic accumulation of plant nutrients, an illumination of 2500 lux is essential. However, the promotion of photosynthesis by light is limited. When it reaches a peak of about 100,000 lux (the peaks of different varieties are different), the promotion of photosynthesis by light is very small. On the contrary, excessive light will damage the plant. The pigment can make plants turn yellow and white or directly burn plants.
The easiest is to use a light meter to measure the illuminance, or refer to the product manual.
What are the grow lights for cannabis cultivation? Their strengths and weaknesses?
The planting lights currently on the market can be divided into three types:
- Fluorescent light
Fluorescent growth lamps come in many different shapes and sizes, from curved bulbs to long tubes. Fluorescent lamps are popular because they can provide efficient and pleasing lighting for humans, and they can also be well suited for herb gardens and other types of low-key indoor gardening without using a lot of electricity.
Low power consumption and less heat generation
Low light intensity and low heat, can illuminate plants very close, very suitable for small spaces
The soft light is very suitable for the seedling stage and cutted plants.
The spectrum is not suitable. Although fluorescent lamps are more efficient in converting electricity into light, only a small amount of this light is suitable for the needs of cannabis. Cannot make cannabis grow huge and bloom densely.
The penetrability is poor, and it can only reach the top of the plant, and cannot fully irradiate the whole plant.
At present, fluorescent lamps are mostly used in the seedling stage and cutting rooting stage of the plant in cannabis cultivation. It is to give the plant a mild light environment for her to stand firm. But it cannot satisfy a plant that is growing and blooming.
- High intensity discharge lamp (HID)
The high-intensity discharge lamp consumes more electric energy, but the conversion efficiency of electric energy is low. It generates a large amount of light energy and also generates a large amount of heat. In order to dissipate heat, a good heat dissipation system must be equipped, and in order to save light energy, a reflector is often equipped.
(1) Metal halide lamp (MH)
The spectrum emitted by this lamp is very suitable for plant growth during the vegetative period.
(2) High pressure sodium lamp (HPS)
The light spectrum of this kind of lamp is more suitable for plants after the pre-flowering period, which will greatly encourage the cannabis to bloom dense flowers.
(3) Ceramic metal halide lamp (CMH) and light-emitting ceramic lamp (LEC)
The general principle is the same as that of metal halide (MH) lamps, but ceramics are used to partially or completely replace the electrified materials, making the luminous efficiency higher than MH lamps.
The amount of luminescence is large. Because of the different luminescence principles, HID lamps consume more electricity and emit more light, which is completely sufficient for the energy supply of hemp.
The spectrum is suitable, and electrical energy is very suitable for hemp absorption after being converted into light energy. Many growers use MH lamps and HPS lamps to match planting to obtain very good results.
Lightweight and easy to arrange.
A lot of heat is generated, and this heat needs to be dissipated by a fan or a water cooling system. If the heat is not timely, the plants will be heated to death, and in serious cases, it will cause a fire. And this high heat is also a loss of life.
Because a cooling system is required, a certain amount of space is required.
There are many parts, it needs to be equipped with reflector, ballast and corresponding wires.
This kind of lamp has high power and high power consumption, which will cause excessive electricity bills and unnecessary attention.
In general, the high efficiency brought by this kind of lamp makes it a professional plant lamp, and the price of itself and supporting facilities is not expensive, and it is currently the choice of many professional growers.
- LED grow light
The lamps with the highest luminous efficiency. The LED grow lights we can see on the market are all equipped with cooling systems and electronic components. It generates little heat and can produce different spectra according to the purpose of the manufacturer.
Ultra-high luminous efficiency, the heat generated during work is very low, usually manufacturers will self-dissipate heat, so there is no need to worry about the trouble caused by excessive heat.
Simple installation, usually all-in-one, just plug in and use.
Low power consumption. Because the spectrum of LEDs can be customized and the conversion rate of light is high, the efficiency of turning electricity into energy absorbed by plants is very high. There is no need for too much electricity to be wasted on unnecessary heat or not. On the required spectrum.
The spectrum is suitable. At present, there are manufacturers that specialize in producing cannabis LED lights. The spectrum is completely suitable for cannabis absorption, almost not much, not much.
The price is high, and the price of really good LED grow lights is more than 1500RMB, because the cost of a good LED single lamp bead is more than 10RMB.
There are many fakes, there is nothing to say about this, after all, it is a celestial dynasty. The publicity is very good, and there are many stories about scrap plastic.
Well, the above is a general description of all kinds of planting lights. I will also write a detailed explanation of each lamp later, and provide some opinions for readers when choosing to compare.