How to measure light intensity for cannabis
As we all know, light is a way for plants to produce food through photosynthesis, so there will be no plants without light. In other words, if there is too much light, the leaves will be saturated and burned. If there is too little light, you will have long and elastic plants. Neither is the best choice. This means that if you want to optimize the final yield of your planting, it is very important to find the best light intensity in your planting room. So what is light intensity? Light intensity is the amount of light energy per unit area. It is the largest near the bulb and decreases rapidly as it is away from the light source.
How much light plants need varies according to each stage of the growth cycle. Seedlings do not need much light, but once the plant enters the nutritional stage, this requirement will change and need almost all the light it can get. This enables plants to reach their full potential. So is flowering. Although flowering plants thrive in different spectra than during vegetables, they still need a lot of light to ensure that the flower buds are as large as possible. For healthy growth and good yield, there is almost nothing more important than providing sufficient light for your cannabis plant.
Light demand of cannabis plant in the whole growth cycle
Clones and seedlings: 5000 – 7000 Lux
Plant growth: 15000 – 50000 Lux
Flowering: 45000 – 65000 Lux
Maximum recommended light: 75000 Lux
There are two measurement methods related to light intensity and brightness, lumen and lux, both of which measure different aspects of light.
Lumens – lumens (LM) are measurements of the visible light or “luminous flux” emitted by a light source. Therefore, a higher lumen measurement is equivalent to a brighter light level in the light source.
Lux lux is a measure of the light that actually falls on a surface, such as a plant leaf. Lux is usually used for light measurement in the planting room because the light energy falling on the plant is more important than the output of the light itself.
Unfortunately, using lumen and lux measurements alone is not enough because they cannot fully sense the concentration of blue and red wavelengths, which are almost invisible to human eyes, but play an important role in plant growth. Instead, growers rely on par and PPFD values to measure horticultural light because they measure more accurately the light that plants can use.
Par – par, or photosynthetic effective radiation, is a measure of the visible spectrum of plants that can be used for photosynthesis, which is between 400-700 nm. Par measurement shows that the position of specific light output can be found in the visible spectrum.
PPFD – on the other hand, PPFD or photosynthetic photon flux density is a measure of the amount of light (PAR) received by plants over time, expressed in micromolar photons per square meter per second (µ mol / M) ²/ s) Is the unit In other words, PPFD measures how many photons hit the plant in one second.
In order to obtain accurate PPFD measurements, it is important to average several different readings from around the growth space. A single, centered reading will distort the actual average that your plants will experience, as most growth lamps tend to focus their light output in the center.
When determining the distance between the grow light and the crops, it is important to consider the plant growth conditions. For example, a height limit affects not only the height of a light, but also the type of light. HID lamps generate a lot of heat and need to be placed further away from the canopy than led grow lamps. In a short growing tent, there is no room for HID lamps at all, which requires reflectors and some cooling.
Just as important as light, height is the footprint of your light or the amount of space it can adequately cover. This is the importance of HID reflector. A reflector (sometimes called a cover) located around the bulb reflects light outward from its light source to form a wider coverage. In general, led plant lights do not have reflectors, which leads many growers to choose to run enough lights in their space to create overlapping footprints.
HID lamps –for HID lamps, it is important to remember that the higher the wattage, the more light and heat generated. Therefore, the HID bulb with lower wattage can be suspended close to the roof. In order to get a complete standard, most measurements are based on 1000 Watt hid bulbs, because at this wattage, the light intensity doubles every 15 cm from the roof. Growers usually install multiple low-power HID lamps on a high-power bulb to achieve greater floor area and more uniform light distribution. In general, a 1000 Watt HPS bulb will produce a floor area of 1.5 x 1.5 meters at a height of 1 meter, and the PPFD reading is 1435 µ mol / m ²/ s。
LED lamps – led plant grow lamps produce significantly less heat. Generally speaking, your led growth lamp should be between 60-90cm above the tree crown for seedlings and cloning, 30-60cm for vegetative growth and 40-90cm for flowering.
Benefits of measuring light
1 – helps increase production
Lux sensors can provide operational dates to increase the yield of cannabis plants – a clear benefit for growers. With it, you can determine the best location in the planting room, or you can use it to determine the appropriate distance from the lamp to the plant.
2 – preventive maintenance: know when to replace the planting lamp
The service life of some types of lamp (MH / s) is limited. Over time, they become darker and darker, which is why they need to be replaced at regular intervals.
3 – prevent some plant problems
Insufficient light and too much light can be harmful to your cannabis plant. An appropriate amount of light, not too much or too little, will reduce the pressure on plants and prevent further problems such as light burns and bleaching.