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How Much Light Do Your Garden Plants Need?

Like humans and other animals, plants need energy to do work. Unlike humans and animals, plants don't eat their food to get this energy. Rather, they use the energy from the sun, namely, light, to make their food. The ingredients for this process are water, air, and light. Plants don’t use all the parts of the air, they only use the carbon dioxide (CO2). The process is called photosynthesis, in which plants convert Carbon Dioxide and light into energy and oxygen.

Increased light duration allows the plant to make sufficient food to survive and grow. Increasing the time plants are exposed to light can be used to compensate for low light intensity, as long as the plant’s flowering cycle is not sensitive to day length.

In some cases you find your plants still alive even under a deficiency of light. While it is possible to survive this way, the plants will not reach their full growth potential. If your plants get plenty of sunlight in your garden, there is still room for additional lights; research has found that long-day plants develop faster with over 12 hours of lighting. In either case you may find supplemental light useful for growing lusher plants.

Limits of Light

Too much light can be harmful to plants. There are two ways plants can get too much light:

Firstly, light that is too intense can damage your plants. 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. Therefore, people protect plants from too much direct sunlight during summer months.

Secondly, excess light duration can affect the growth cycle and blooming of many plants. Limits of light intensity and duration vary between plant species. Plants require some period of darkness to properly develop and should be exposed to light for no more than 16 hours per day.

Light Intensity (how strong the light is)

Light intensity is defined as the power/luminous flux emitted/received per unit area. The light intensity requirements differ for different plant species at different growth stages.

Due to the size of leaves and the limited amount of chlorophyll content, the plants have a photons uptake limit (The Photosynthesis rate limit). We could not radiate extremely high-intensity light within a short period to prevent the plateau/inhabitation effect in photosynthesis. Instead, we should follow the photoperiodism behavior and the plants' spectrum requirement to optimize the radiation efficiency.

Because the plant has its own limit, when a plant is exposed to high intensity light, not all energy is absorbed. Some of the light energy is wasted, but some is converted to heat. Additionally, of the sunlight that reaches Earth's surface, 54% is already heat (infrared), 45% is visible light, and about 1% at shorter wavelengths (ultraviolet). Your plant has to dissipate this heat energy, which normally involves using some of its available water to cool itself off. Over time, this can deplete the plant’s water reserves and leave insufficient water for vital processes such as photosynthesis. If heat generated exceeds the plant’s ability to dissipate it, the plant will suffer heat damage. This often presents as yellow or brown spots on the foliage, generally yellow leaves, brown crispy leaf edges or tips, or curled, dropping leaves.

Compared to over half of the sunlight having heat (infrared) incorporated, artificial light like LED has almost no heat in the beam. That means there is little to no risk of heat damage on the plant because of too much light intensity.

Light Duration (how many hours)

Being exposed to light for too long can affect a plant’s growth cycle and ability to bloom but this differs based on the type of plant. Some plants cannot trigger important phases of growth or bloom without appropriate levels of darkness per day. These plants exhibit photoperiodism.

Basically, plants are generally classified into short-day plants, long-day plants, and day-neutral plants according to the photoperiod’s requirement. Short-day plants grow better and form flowers only when lighting duration is less than about 12 hours, while long-day plants develop faster with over 12 hours of lighting and only need 6 hours of darkness to rest. Therefore, one should check whether their plant is a short-day plant or long-day plant to determine the best duration of lighting.

Overall, plant growth cycles tend to be impacted by the duration of light, but the plants are not as harmed as over-intense light.

Best Strategy for Lighting

Due to LED lights having no risks of overheating to damage the plant, modern growerst use LED light to grow plants with high spectrum quality light. At least you can’t go wrong with over lighting the plants.

Natural Sunlight (8 hours) + Supplemental LED Light (4-6 hours)

Enough lighting ensures a sufficient level of photosynthesis for plants can be carried out to generate energy to sustain their growth. When the plants lack lighting, the leaves will seem paler or even look yellow / white. The form of the plants will also look skinny, as they tend to be extending their stems trying to reach more sunlight for growth. If your plants are flowering plants, they may even fail to produce any buds. Total lighting duration is one of the critical parameters you should be aware of when growing plants in your desired scenario. It is very important to shine your plants in a correct way in order to optimize their growth and prevent damages.

While different states may have a different solar time according to their latitude, and plants need a variety of solar radiation according to their species & growth stage. The first thing we suggest doing after getting a supplemental light is to check the light requirement of your plant at specific growth stages.

A more precise way to calculate the best light duration is to use the DLI chart.

DLI stands for Daily Light Integral, and it is one of the typical units to describe the required amount of light (mol of photons) received by the plant per meter in a day. DLI is equal to PPFD x light hours per day(hDL) x 3.6 x 10e-4 (unit: mol/meter/day).

PPFD Stand for Photosynthetic Photon Flux Density, calculated by the PPF received on a unit area(m2). Since the area receiving the photon is proportional to the distance, the PPFD far from the light source will be decreased accordingly.

If you know your plant DLI and the PPFD of the light source, you can quickly look up the hours needed for your plants.

Below are some common long-day plants’ DLI.


As most plants fall in the window of 8-16 hours of lighting, we suggest applying both natural sunlight and supplemental light for the best plant growth.

Natural Sunlight (8 hours) + Supplemental Light (4-6 hours)

In this formula, as artificial light is one source of light for growing plants, the quality of light or wavelength must be carefully considered. Plants require mostly blue and red light for photosynthesis, but for flowering, infrared light is also needed. Incandescent lights produce mostly red and some infrared light, but very little blue light. Fluorescent lights vary according to the amount of phosphorus used by the manufacturer. Cool-white lights produce mostly blue light and are low in red light; they are cool enough to position quite close to plants. That’s why some LED grow lights like SOL-GROW have pre-tuned the specific spectrum for both crops and flowers to ensure you get the best results.

Operationally, 6-hour non-stop supplemental lighting seems hard to achieve - you can let SOL-GROW kick in to help your plant growing goals. It comes with 6-hour non-stop supplemental lighting, powered by free solar energy and can stick it anywhere in the soil of your garden, making the very important light source a nonissue to the plant.

By observing the lighting requirement and health of your plants, you will be able to adjust the tools and the plant position to optimize their growth.

Still confused? Feel free to contact us and our specialist will be more than happy to assist you with the full set of solution.

“OmniPV is a team of clean energy enthusiasts who has a strong commitment to provide the best service and high-quality products to our customers”


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