During the flowering stage, you should decrease the DLI and increase the light intensity. The photoperiod should be 12 hours during the flowering stage. And 18 hours during the vegetative stage. When you increase the light intensity, your hemp plant is going to need water and nutrients.
Light Intensity for Flower
Studies have shown that increased light intensity is directly linked to increased harvest size and higher concentrations of cannabinoids. Most cultivators suggest increasing light intensity to 800 to 1500 µmol/m2/s PPFD during flower.
The greatest amount of intensity should be used during Weeks 3 through 6. It is during Weeks 3, 4, 5, and 6 that the plants go through the most maturity growth. There is where bud development occurs. It is during these weeks that we want the greatest amount of light intensity.
Faster flowering can result in significant savings and better profitability for plant breeders. Various conditions can affect the flowering speed, but the quality of the light spectrum is probably the most important.
Light intensity influences the manufacture of plant food, stem length, leaf color and flowering. Generally speaking, plants grown in low light tend to be spindly with light green leaves. A similar plant grown in very bright light tends to be shorter, better branches, and have larger, dark green leaves.
Light Intensity and Yields
The light intensity rule of thumb is that a 1% increase in light equals to a 1% percent increase in yield. In a study by Wageninen University, they discovered this to be true of all horticultural crops they evaluated including, fruiting (vine) crops and flowers.
As you rise from low light intensity to higher light intensity, the rate of photosynthesis will increase because there is more light available to drive the reactions of photosynthesis.
Myth #14: LED Lights Can't Damage Plants
The reality is that modern LED grow lights can produce a very high level of light and it can cause photo-bleaching and burn leaves. This depends very much on the plant, but a PPFD of 800 is enough to damage some plants.
Manufacturers' guides often tell you not to dim the LEDs until the plant bloom, but this is impractical. Your plant will be dim unless you dim at least somewhat during seedling phases. The solution is choosing LED grow lights dimmable that are most likely to work well with dimming and keep your plants thriving.
In general, blue light spectrums encourage vegetative and structural growth and red light promotes flowering, fruit, leaf growth, and stem elongation.
When plants lack light, they don't produce chlorophyll (the green pigment in plants), and plants can turn pale green to yellow to white. Plant stems become “leggy,” meaning stems become long and thin and appear to be reaching toward the source of light.
Pale green and yellow leaves that drop off are a sure sign of inadequate sunlight. Also, with variegated plants, the leaves will revert to a solid green color so the chlorophyll within can do its job. If your typically colorful plant has lost its color, move it to a sunnier place and see its color return.
The most apparent sign is leaf burning. This typically causes the yellowing of leaves at the top of the plant but the veins stay green, and the leaves take on a yellow or brown, burnt look.
Because bud formation starts after 7 hours of dark period, it is also wise to always maintain a minimum day length of 17 to 18 hours during the vegetative period. A dark period of 12 hours is used as a standard in cannabis to ensure a smooth flowering process.
However, at a higher intensity (such as 20 µmol∙m–2∙s–1 or higher), blue light can promote flowering of long-day plants and inhibit flowering of short-day plants.
High Intensity Discharge (HID) Grow Lights. HID lamps are considered the most effective for growing cannabis. Compared to fluorescent lighting, you get a better ratio of yield and watts used. Another advantage of HIDs is that they are easy to use.
A:LED grow lights are now powerful enough and full spectrum enough to be considered the ideal choice for cannabis grow lights. With the correct umols and PAR value, an LED grow light will deliver larger and thicker results than an HID or High pressure sodium light.
Generally yes, you can use any LED Light to grow plants, especially white LEDs as they have a good mix of different wavelengths plants need. However, regular LEDs typically don't have sufficient light output or power to help plants flower.
For the wattage between 200W to 400W, keep the LED grow light about 12 inches to 20 inches from plants. The height about 20 inches to 28 inches is suitable for LED grow light in 400W to 600W. For up to 800W, LED grow light can be placed up to 38 inches above the plants.
If a plant is getting too much light and suffering from high light stress, its leaves may look as though they have burned or simply are falling off. In many cases, the soil will be dry to the touch, too.
First, for young plants, keep the light 36-48 inches away at 50% intensity. In the flowering stage, plants can often take more light intensity. In the first couple weeks of flower, you can ramp up the intensity to 100% and afterward, start decreasing the distance to about 18-24″ at a rate of 1-3″ per day.
Improper watering is the common cause of leaf scorch. Too much fertilizer can cause leaf spots and marginal burning. Scorched tree leaves can drop prematurely.
The first thing to know is that plants typically absorb red and blue light. And natural sunlight is in the range of 2,700 to 7,000 Kelvin. So, as a general rule of thumb, if you're looking to promote vegetative growth, pick lights ranging between 5,000 and 7,000 Kelvin.
The main reason why green light is purportedly not useful to plants is because it is poorly absorbed by chlorophyll. However, absorption of chlorophyll is usually measured using extracted and purified chlorophyll, in a test tube (in vitro), and not using an intact leaf (in vivo).
Best growth occurs above 750 foot-candles unless plants also receive extended periods of direct sunlight. Give them artificial light in the 500 to 1,000 foot-candle range, or 15 or more watts per square foot of growing area.