Cannabis Grow Lights: How High Light Intensity Impacts Growth (2024)

FAQs

When should I increase my cannabis light intensity? ›

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.

Too much light can harm cannabis plants, and a thoughtful grower needs to be strategic about the placement and strength of light sources in a greenhouse environment.

Studies have shown increasing the light intensity can have a positive effect on plant photosynthesis and/or growth of Cannabis.

Telltale Signs of Too Much Light

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.

However, plants require some period of darkness to properly develop and should be exposed to light for no more than 16 hours per day. Excessive light is as harmful as too little.. When a plant gets too much direct light, the leaves become pale, sometimes burn, turn brown and die.

If your plants surpass the maximum PPFD range, damage can occur. Overall, if you exceed the maximum PPFD for your cannabis crop, the plants will exhibit leaf burn and the overall health of the crop will decline.

Sufficient lighting is essential for all stages of growth, but sometimes you can overdo it - leading to light stress in plants. This can cause a variety of issues with your plants. This can get tricky, because you absolutely need intense lighting to produce strong root systems to develop fruits and flowers.

Red Light (620nm-700nm)

but if plants are grown under only red light. They will have a stretched and elongated appearance. The leaves are long and thin and plants become tall.

Most flowering plants grow best with 20-30 watts of light per square foot. Don't make the mistake of thinking more is better. Too much light can lead to bleaching and burning your plants.

With that said, plants generally use light to perform the process of photosynthesis which uses the light energy to combine CO2 with water to make sugars and 02. The higher the light intensity, the more rapid this process can proceed. Thus, most plants grow faster in higher light intensities.

What light intensity is best for flowering? ›

Up to 2000 PPFD matching the sun's intensity. Mammoth recommends to target 600 – 900 ppfd in Veg and 1100 – 1500ppfd in flower.

To some degree, more light translates to fatter buds and higher yields (you'll need to pay attention to the distance between your grow light and plants or your plant may suffer from light burn). Increasing light intensity is the most effective way to fatten up buds.

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.

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.

Symptoms of excess sunlight on indoor plants

Damage appears as pale, bleached or faded areas. These areas eventually become brown and brittle. Symptoms are more severe when strong sun is combined with dry soil conditions.

Medium light intensity plants prefer 250 to 1,000 foot-candles. 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.

Intense, direct light is great for some plants, but it will damage (or even kill others). The plant isn't able to convert all of the light into consumable energy, and the excess creates a heat issue over time. The plant might use available water to cool itself, which creates a moisture shortage as well.

Plant height, stem diameter, and fresh weight were significantly increased or decreased with changing light intensity. The 50% and 65% shading treatments improved plant height, stem diameter and fresh weight of biomass of A. elata, whereas 80% shading revealed harmful effects with a significant decrease (p < .

A limiting factor could be the amount of chlorophyll molecules that are absorbing the light. At a very high intensity of light, the rate of photosynthesis would drop quickly as the light starts to damage the plant. This is a very important aspect of photosynthesis.

Where the plant is in the plant lifecycle also has an impact on their optimal PPFD levels. For example, younger plants that are still growing will survive better with lower PPFD, while plants that are flowering or fruiting will require higher PPFD levels.

Do plants under grow lights need a rest period? ›

A: In general, you should not leave grow lights on 24/7. Plants need a light-dark cycle to develop properly. It's believed that they truly do “rest” during periods of darkness, and probably use this time to move nutrients into their extremities while taking a break from growing.

For a cultivation area or a grow tent of 80 x 80, you will need LED systems from 100W to 200W depending on the manufacturer. Any LED system between these watts will be enough to fully grow up to 4 plants.

If you leave the lights on all the time, it messes with plants' circadian rhythm and can stunt growth as well. Location is Everything – grow lights should sit no more than 3″ above the leaves of seedlings. Anything further away will cause legginess as the plants reach for the light source.

Red radiation (around 700nm) is considered most efficient at driving photosynthesis – especially in the flowering stage for biomass growth (important to Cannabis growers).

Light intensity

Light is the most important factor when trying to get denser cannabis flowers because lights help cannabis plants produce sugars through the photosynthesis process which helps them grow, just have in mind that not any light will do, weed needs an optimal light intensity to produce big fat buds.

Effects of Light Intensity on Plant Growth. Clear external differences were observed among plants grown under 60 days of different light intensities. Compared with high light intensities (L3, L4, and L5), leaf areas were higher under low light intensities (L1 and L2). L2 resulted in the highest leaf area.

Studies have shown that the number of floral buds increases in individual plants (and the days to flowering decrease) when supplemental, artificial light is applied, which indicates that light intensity affects floral induction and can feasibly enhance the yield (Choi et al., 2016).

A dimmed light won't provide the same exclusive spectral distribution and can change the quality of plant growth. It's understandable that some growers may want to dim their grow lights, but it's best to keep your lamps at full power.

For higher yields indoor, you want your plants to grow wide rather than tall. You want a bushier plant so more buds have access to direct light, rather than a long, lanky plant with several buds hidden under a canopy. By transferring your plants to larger containers, you can encourage more outward expansion.

To grow the densest, biggest buds possible, your plants need plenty of light. If you're growing outdoors, make sure your plants receive at least 6-8 hours of sunlight a day, but 10-12 is optimal. Put your plants on a south-facing slope and they'll get the most sun possible.

How do you get big colas? ›

Topping to increase the number of colas

Topping is a form of pruning and involves pruning off the branch tip of the main cola. When you top the main cola, the energy goes to the side branches. The next two lateral branches will become the main branches. Topping will increase the overall yield of your grow.

For the biggest yield, you must use High Intensity Discharge (HID) lighting. Metal Halide (MH) or High-Pressure Sodium (HPS) lights are the indoor grower's choice for plant production and heavy harvests.

The longer you keep your plants in the vegetative stage, the bigger your plant will be, resulting in bigger yields from plants that were vegetated longer.

What LED is equivalent to a 1000w hps? 1000W LED lighting fixtures typically have an output close to 900 watts of HPS light. They can deliver light that lasts longer and have a lower energy consumption.

The flowering stage occurs naturally when plants receive less than 12 hours of light a day. For cannabis to completely enter the flowering stage it requires periods of 10 to 12 hours of complete darkness.

Week 3. Your cannabis plants have still not entirely stopped growing and will now be about 50% bigger than what they were just three weeks earlier. Although still stretching a bit, the stretch will now gradually slow down and soon come to a complete halt.

If plants have a short-day response, then shortening the days by totally excluding light from the plants for 12 hours per day will accelerate flowering.

A lack of sufficient light causes the plant to grow long spaces on stems between the leaf nodes (the point where a leaf grows out from the stem). Plants without sufficient light may also drop their leaves, especially older leaves.

Once the light cycle is changed to 12 hours, adding more light to the plants helps increase the flowers and yield.

Height of plant: Depending on the strain, plants will generally double in size during flowering. So, if 'room' height is limited, the switch to 12/12 will need to be done no later than when the plant has reached 50% of the 'available' height (remember to consider the minimum gap distance between lamp and foliage).

How do you maximize yield in flowering? ›

During flowering, switch the lighting schedule to 12 hours on and 12 hours off. The key for maximum yields is to provide large amounts of light and to distribute it as evenly as possible across the canopy. Space your lights accordingly.

An even canopy means each plant gets a maximized light exposure. Maximum light exposure means more chance for the plants to grow big buds. Typically cannabis plants have a single central cola. As the plants grow, tying the branches to the screen or net trains the plants to produce colas from each branch.

Overall, these results suggested that 400 and 500 μmol m⁻² s⁻¹ is the optimum light intensity which positively changed the leaf orientation and adjusts leaf angle to perpendicular to coming light, consequently, soybean plants grow well under prevailing conditions.

12 or more hours of darkness is the biological trigger for photoperiod cannabis to bloom. Outdoors, as the nights grow longer incrementally from the summer solstice onward, some strains can even begin flowering when receiving 14 hours of sunlight.

This method typically involves a height-based flowering switch. Sativas are usually switched when they reach 30–45cm, since they grow so much during the flowering stage. Indicas are switched when they reach a height of around 100cm, giving them more time in the vegetative state.

Generally, you want to water every 2 or 3 days during Flower and you want to water enough that 10-20% of water comes out from the pot as runoff. You can check your soil moisture by sticking a finger in the pot: if the soil is dry a couple inches down, then it is time to water again.