Growing A Plant With Artificial Light Is Possible If You Know How: The Mega-Guide To LED Lighting For Indoor Plants

Light energy and vegetable pigments

Light is a type of electromagnetic radiation, and as such, it travels in waves, just like radio waves, microwaves, or X-rays. In waves, the distance from the crest (top) of one wave to the next is known as wavelength, and it will be characteristic of each type of radiation. The unit of measurement is the nanometer (nm), one-millionth of a meter. The radiations that have long wavelengths, such as radio waves or microwaves, have less energy (note in the following image that the distance between crests is greater), unlike those more dangerous radiations such as X or gamma rays where the wavelength wave is short and therefore transmit much more energy.

Within this electromagnetic spectrum, our eyes only cover what appears as visible light, which ranges from 400 to 700 nm. Although the light which we see appears white to us, it has all the “colors” of light, that is, all the wavelengths comprised within visible light (the rainbow is an example).

The plants are going to go a little bit beyond our sight. They will be able to perceive wavelengths greater than 700 nm, getting into the infrared and less than 400 nm, going to the zone of ultraviolet radiation, although the really important zone is between 400 and 700 nm and that is where the energy used by the plant for photosynthesis, called photosynthetically active radiation (PAR).

And how do they perceive it if they don’t have eyes? We have cones and rods in the retina that are responsible for our vision, but in the case of plants, they are specialized molecules called pigments. There are different types of pigments and they will perceive a specific wavelength of light. In addition to chlorophyll, which is the best known (and abundant) responsible for the green color of plants, we will find cryptochromes and phytochromes, among others. For example, UV-B light receptors (280-320 nm); cryptochromes, which mainly absorb uv-A (320-390 nm) and blue (400-500 nm) light; chlorophylls, which absorb blue and red light (600-700 nm); carotenoids, which absorb green and yellow light (400-600 nm), and phytochromes, which absorb red and far-red light (700-800 nm).

What should the light of our plants have?

To know the best light that we can provide our plants, we need to take into account the three factors that most affect their growth :

Light quality

With quality, we refer to the color or the sum of colors that make up the light that reaches the plant. All the wavelengths within their absorption spectrum are important for plants, but they prefer blue and red, basically because, depending on the stage of their life they are in, it helps them develop or provides them with information. extra that can be very valuable, as is the case with red and far red. Green, let us not forget, is not absorbed by plants but rather reflected, and that is why we see them in that color.

• Blue. Between 400-500 nm. It is the color that favors vegetative growth, that is, from the time the seedling germinates until it blooms. If we only provide this color, the plant will have short stature and a darker green.

• Red/Far Red. Between 600-700 nm. This relationship affects the length of the stem and favors flowering. The red/far red ratio informs them if they have other plants too close and therefore they may be taking away light, in this case activating the shadow escape protocol. More far-red (i.e., lower red/far-red ratio), as is the case with incandescent bulbs, favors more length between leaves on the same stem, resulting in a taller plant. Therefore, the best option is a combination of blue and red light since this ratio is the most beneficial for plant growth.

Light duration

An excess of light can be as damaging to plants as a prolonged absence. We also know this parameter as a photoperiod, that is, the number of hours of light followed throughout 24 hours. Over the year, the number of daylight hours varies, right? We have more daylight hours in spring and summer and less in autumn and winter. Plants are adapted to this in nature, but even so, there are plants that prefer to flower in short-day periods (8 hours of light and 16 hours of darkness), others that will have long days (16 hours of light and 8 of darkness) and others, of the neutral day; it will give them the same because flowering will not depend on the hours of light and darkness but will be induced by other factors.

The needs will change depending on the flowers or crops that we want to grow since their requirements will be different, but, in any case, they all need a break and rest for a while in the dark. For example, as long-day crops, we have summer flowers and some vegetables, such as onions, lettuce, spinach, and potatoes. Indoor plants usually have a short day (remember that they do not need as much light as if they were outdoors). As for neutral day we have tomatoes, cucumbers, and some strawberries. Once the number of hours of light and darkness has been established, it is best to attach a timer to the artificial light that turns the light on and off automatically.

Light intensity

The most critical moment for the growth of the plant is at the beginning when it begins to germinate. It is the phase in which they need the greatest amount of light, like a baby that requires the greatest care. Keep this in mind if you are putting seedbeds and you are going to set up your small garden from scratch.

When they are tiny, it is advisable to put the artificial light bulb (if they do not have enough natural light) at a height of about 5-7 cm and raise it as they grow so that they are always about 8-10 cm from the light source. In indoor plants with flowers that are already adults, 25-30 cm tall is fine and if they are plants grown for their foliage, we can put it at 90 cm.

So what light do I put on my plants?

Once we are clear about the quality, duration, and intensity of the light that our plants need inside the house, the key question arises: what light to put on the plants? In the following figure, we will see some sources of artificial light. Look at the first diagram that represents natural light from the sun. That is the ideal for plants and the one we should try to reproduce.

Remember that within the useful area of ​​the spectrum, red and blue light (or better still, the combination of both) is the most important.

Incandescent lamps

Incandescent lamps emit light with a continuous spectrum (this is positive) although it is poor in blues and rich in reds. Even so, in the absence of natural light, they can provide quantity and quality of light. They have been widely used up to now due to their low price, broad spectrum emission, variety of shapes, use in direct and alternating current, different voltages, etc.

On the contrary, they are very polluting systems, with low light output (only 10-15% of the energy consumed by the lamp is transformed into light and the rest is heat) and short useful life (500-1000 h). , reasons for which, the tendency is for them to disappear. The European Union and some countries have banned the manufacture and sale of incandescent lamps with low energy efficiency, to increase energy efficiency and, therefore, save energy.

Halogen lamps

Incandescent lamps were perfected and gave rise to halogen lamps, based on the same principle, but with better luminous and color performance, although, yes, they reached such a high temperature that it was difficult not to get burned if it was handled while it was on. For practically the same reasons as the previous ones, the EU began to withdraw them in 2009, and in 2018 the manufacture and import of halogens for most uses came to an end.

High-Intensity Discharge (HID) Lamps

High-Intensity Discharge (HID) lamps are used to supplement light during the day or replace this part of the night. Within the HID are high-pressure mercury lamps, high and low-pressure sodium, and metal halide lamps. High-pressure sodium vapor is still widely used today in public lighting (those orange lampposts, roads, and tunnels… for example).

These lamps have a completely different operation than incandescent ones. They stand out for their great economy in operation, thanks to the fact that they generate an extremely high luminous flux in a very small space, they emit almost no heat, excellent color reproduction, and long duration are other advantages of high-pressure discharge lamps, in addition of its compact construction, which facilitates the orientation of the light.

The spectrum of light that they emit is not continuous, unlike incandescent and halogen bulbs, but it presents important peaks in blue and red that ensure the balanced growth of our plants. On the contrary, they are very dangerous lamps due to the type of waste they generate and the possibility of poisoning (specifically with mercury and metal halide).

Fluorescent lamps

Moving on to energy efficiency and safety (well, this is relative), we find fluorescent lamps. They are low-pressure mercury vapor discharge lamps. Inside the tube, we will find a small amount of mercury vapor and an inert gas, normally neon or argon. The tungsten filament that is at the end of the tube is the one that, once red hot, ionizes the gases inside.

The fluorescent ones are very suitable for growth, for scions, and for rooting cuttings, which is why they are especially recommended during the first stages of plant growth. Among their advantages, we highlight that they are quite economical, have high luminous efficiency and useful life (5000 – 75,000 hours), as well as a wide variety of color tones which, being diffuse, means visual comfort and do not emit too much color. However, they take up more space, they have a flicker that can be somewhat annoying (and that is corrected with an electronic ballast), their turn-on time is appreciable, and, in addition, the multiple turns on and off can reduce their useful life (also corrected by the use of the ballast). It should be noted that due to the presence of mercury vapor they are considered hazardous waste and there is a possibility of poisoning by this vapor.

Standard fluorescent bulbs may not be the best for home lighting, but they are great for supplementing natural light for houseplants or starting seedlings. Their cooler light makes them one-dimensional, so they’re ideal when the goal is lush foliage, not flowers. Since this light does not damage the leaves of the plants by not emitting too much heat, they can be placed at a low height.

But within the fluorescents, we also find compact or low consumption ones that have the following advantages over the previous ones: their low consumption, high luminous efficiency, little heat emission, they are small, spectral quality, and long life. Despite being somewhat more expensive, their longevity and energy efficiency make them considered an option to take into account since they are profitable in the long term.

Full-spectrum compact fluorescent (CFL) lights are the best choice as they provide a balance of warm and cool light (red and blue) that accurately reproduces natural light. Available in tube and bulb forms, CFL grows lights are more intense than standard fluorescent lights.

Latest generation: LEDs

Finally, LED lights (Light Emitting Diode), seem to have come to stay and over time supersede all the previous ones. Its use began discreetly for signage, step markings, or level changes, but a series of attractive features and the unquestionable advantages they present have made their development and implementation for multiple applications unstoppable.

Due to their variety, they allow us to choose the color of the emitted light since they offer light of different wavelengths. We find a diversity of shapes (ceiling lights, spotlights, tubes…) that are easy to handle since, as they do not contain toxic compounds, they do not cause health or environmental problems, making them the most ecological option. In addition, they represent great energy savings thanks to low consumption, high luminosity and hardness, low maintenance, and long life.

In the scientific literature, we can find numerous works on the use of LEDs in the cultivation of plants, where they are used as the only source of lighting or as a light supplement. As we already know by now, the energy zone used by plants is between 400 and 700 nm, regions where pigments use that absorbed energy to carry out their fundamental processes.

The combination of red and blue light from LEDs allows good growth and development of plants since it is found in the most important regions, although it is true that monochromatic red light at 680 nm seems to be 36% more efficient for photosynthesis. than the monochromatic blue at 460 nm.

Looking at the above figure of artificial light spectrums, it seems logical to combine a cool white (blue) LED with a warm white (red) LED to provide all the necessary spectrum. In this way, we can achieve “isolated” colors from a light source since we provide the blue light and the red light that the plant needs without providing anything more than what is necessary for growth and flowering. With this, we could save on energy costs, because why light with others like green if the plant does not absorb it?

Having a vertical garden at home or a small indoor crop has become fashionable in recent times, so manufacturers have stepped up and today we have ‘grow’ LEDs that combine blue light in a single source and red. voila. They are narrow-spectrum LED grow lights and are not to be confused with regular LEDs. They provide a purplish-looking light as they contain blue and red bulbs.

If you like to illuminate the living room or a bathroom with purple like a pub, go ahead. But if we want the same effect on plants and ‘normal’ light, we would have to use wide-spectrum ‘grow’ LEDs. That is, we will see it white (like natural visible light) and it will provide the entire useful spectrum for the plant, including blue and red, of course.

What you have to look at if you want plants with artificial light

We have a good variety of artificial lights on the market that are increasingly efficient and respectful, although it is clear that LED lights are gaining ground because their qualities are unbeatable and provide quality light for the growth of your plants. The important thing before deciding on one type or another is that you take into account:

1. Will they be in an area with little natural light or nothing is reaching them?
2. What plants do you want to grow/enjoy at home? Remember that the photoperiod can be different.
3. You must use the appropriate light for the specific growth phase (germination, vegetative growth, flowering)

Once we have this clear, there are all kinds of forms of light sources: attached to flexible arms such as flexo or fixed floor lamps, or hanging from the ceiling, but, in any case, it is advisable to attach timers and remote controls to program the ignition. already paid. Plants like us need a few hours of rest.

If after reading the entire article you are not clear at all, keep it simple: blue (cold) light for germination and growth and warm (red) light for flower production. Or better, a broad spectrum and that’s it. In your trusted store, they will surely be happy to help you.