How long to keep grow lights on plants?

How long to keep grow lights on plants?

Sufficient light is essential for the health and growth of plants. However, there is a serious lack of light for our house plants in our homes, especially in our northern regions. Most of them come from brightly lit places like the tropics and deserts, at least for everything that is currently in. You have to understand that even if our house seems very bright to us, there is a huge difference in light with the outside. On a cloudy day, we find outside lighting around 15,000 lux (unit of brightness) while we consider a well-lit house around 500 lux! This means that even tropical rainforest plants that grow in the shade of tall trees enjoy infinitely more light than our house lighting. This is why artificial lighting is often essential if we want our indoor plants to thrive instead of vegetating in semi-dormancy from September to March! A little theory will help us understand the process.

What are artificial and grow lights?

It can be used in addition to natural light, depending on the number of hours of sunshine missing from the plants, or as a single light source. However, not all artificial lights are created equal for plants. These have 3 types of photoreceptors (photon receptors, elementary particles of light):

  • Those which are sensitive to red light (phytochromes) are the most versatile: they are used for germination, for the formation of chlorophyll, for flowering, among others.
  • Those who are sensitive to blue light (phototropin) adapt the “shape” that allows it to capture more and more light.
  • Those who are sensitive to blue and ultraviolet light (cryptochromes) have an action on the growth of stems and leaves, on flowering …

Each color has a wavelength, plants perceive reds and blues, so they use the waves emitted between 445 and 750 nm (nanometric wavelength). The human eye perceives colors between 400 and 750 nm. Good artificial light for indoor plants must therefore emit these wavelengths to be useful for their photosynthesis.

In addition, the needs of this or that light will depend on the phase of the plant’s development: they rather use blue light when they are in the growth period (between 400 and 500 nm) and rather red light when they are growing. ‘they are in the flowering period (between 620 and 780 nm).

Let’s see different types of grow lights:

Fluorescent lamps

Efficient and quite affordable in terms of price, fluorescent lamps are to be chosen according to the needs and form fairly good lighting for indoor plants. These lamps are, in fact, neon, adapted in the form of a bulb. They are low in energy consumption.

Energy-saving grows lights are lamps found in garden centers, specific for plants because they offer them the light spectrum that is suitable for them. They consist of a compact fluorescent lamp, a reflector, and a switch. This reflector illuminates the entire surface of the foliage and focuses the light on the plant.

The Cool White color (cold white, therefore with blue) is the most efficient for development and foliage, while the Warm White (warm white, therefore with red) favors flowering.


One of the most common systems for lighting indoor plants is the LED. Offering a light very close to natural light, LEDs do not heat up and have an extremely long lifespan in addition to consuming practically nothing. Aesthetic, they fit into any interior. They are very effective for indoor plants as well as for seedlings, providing growths up to 4 times greater than growth under fluorescent lights. Horticulture has also seized these led grow lights to promote growth and flowering and fruiting of plants.

Led grow lights are also able to be declined in all the colors of the spectrum, in this case, for plants in blue and red only. You will find LED grow lights, flowering lights, mixed ones that typically offer 80% red light and 20% blue light to suit the greatest number of plants, and customizable ones.

How to maintain indoor plants under artificial lighting?

Plants used to natural light need to adapt to artificial lighting and will take some time to do so – a few weeks at least, sometimes a few months for some. You should, therefore, not worry too much about this adaptation during the first weeks of autumn when the plants come back. It should also be understood that all plants do not come from the same environments. Tropical plants live in an environment that has almost the same amount of light all year round. However, this is not the case with other plants that come from environments that have winters and which therefore need a period of rest. It is better than leaving them in semi-dormancy for a longer or shorter period depending on the plant, which means less light, no fertilization, and little watering.

The Best Artificial Lighting Systems

Whatever system is chosen, it must cover the entire surface where the plants are located with light, have a reflector that directs the light towards the plants, and emit intense light.

There are three systems equipped with best led grow lights, neon lights, and incandescent lights:

  • An LED lighting system is by far the best possible lighting for indoor plants. In addition, these systems are generally more aesthetic. There is now neon typeled grow lights that are especially suitable for people who have many plants or who are making seedlings. Plants under LED lights grow 4 times faster than under a neon system and incomparably more than under an incandescent system.
  • Second, neon systems are quite effective but far behind LED light systems. Strangely, systems equipped only with Cool White fluorescents were found to be more effective than those equipped with both traditional Cool and Warm White. In addition, for maximum efficiency, neon lights should be replaced at least every two years.
  • Not surprisingly, systems with incandescent lamps have proven to be very poor performers.

Which lighting for which indoor plant?

Indoor plants do not all have the same needs, and these are determined by their natural environment: cacti, for example, live in deserts; they need as much sun as possible; ferns, on the other hand, live in forests, the light is greatly filtered by the trees.

Plants that love light

You will provide around 16 to 18 hours of light per day for those of your houseplants that have high needs. However, all do not have the same tastes; there are:

  • Those who like direct sun, which will therefore be placed near a window facing south, such as ficus, Beauharnais or phoenix, as well as succulents or carnivores;
  • And those who prefer western exposure, very bright but without the sun or at the very end of the day when it is the softest: spathiphyllum, cycas, Schefflera, for example.

Plants that prefer partial shade

Plants with green foliage are generally less greedy; give them on average between 12 and 14 hours of daily lighting.


If our budget allows it, it is clearly clear that we should prefer a system with the best led grow lights, especially since these lamps do not heat and take little energy, therefore are more economical.


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