What is the Optimal Light Spectrum for Plant Growth

LED lights for plant growth.
Perhaps you decided to start indoor gardening because it’s now snowy and icy outside. However, you may have found out you have more to learn about the optimal light spectrum for plant growth.

Before we explain the optimal light spectrum for plant growth, we’re going to remind you what the light spectrum is. When speaking of the light used to develop indoor plants, it’s a source of lamp that has one or more colors of the visible light spectrum in it.

Some growers stick with a single-spectrum wave lamp for each growth stage, such as red or blue. Others might use full-spectrum light, which consists of all the visible colors of the rainbow and the sun. It depends on your objectives when setting up your growing environment.

Factors that Determine Optimal Light Spectrum for Plant Growth

If you have no idea what we’re talking about yet, don’t worry. You’ll learn soon enough. The short answer is, the optimal light spectrum for plant growth depends upon a variety of factors.

Stage of Plant Growth 

You may have seen explanations of the plant growth cycle divided into different stages. Not all sources will use the same terms. However, you may be familiar with germination, sprouting and seedling, vegetative and flowering, or ripening and maturing used to describe the stages.

The primary stages we’re concerned with include the seedling, vegetative and flowering stages. During the seedling stages, we typically recommend the blue light spectrum. If you’re not sure on the specific “nanometer” reading, start with between 450 and 490.

A little bit longer of a range of blue during the time when your plants begin to sprout is fine too. If your grow light offers a blue-green spectrum range, that would work as well. By the way, a “seedling” is the time during which a plant begins to shoot out and up above the soil.

Before a plant becomes a seedling, it’s under the ground. At that time, it’s still in the “germination” process. From a seedling, a plant sprouts and ends up transitioning into the “vegetative” stages. At this point, the plant may still need blue light.

As soon as the plant starts to bud, at that point, you may want to add some red spectrum lighting. This usually measures about 700. A little lower and a little higher, from about 650-750 may work for you too.

Initial Indoor Growing Budget

Sometimes, the cost of setting up a grow room can feel overwhelming. If you want to get started on a lower budget, you may want to consider installing a full-spectrum light. It can provide you with the optimal light spectrum for plant growth at least on a smaller scale.

Perhaps you can set up an experiment to start. Add at least one full-spectrum (white) LED to your growing environment. Make sure you only place as many plants as will fit underneath it, leaving about a foot or two space between the stems – if you’re growing from a starter plant.

Most starter plants, by the way, start out as either a seedling or a crop in its vegetative stage. If you do this, it could increase your chances of growing indoors on a budget your first time out.

Back to the recommendation of a full-spectrum light: It’s because it will offer you all the visible light waves. You won’t have to necessarily buy any single-spectrum lights, such as red or blue lamps, right away.

Bear in mind that LED full-spectrum lighting systems may cost more than other lighting systems, such as fluorescent, incandescent or high-pressure sodium lamps. If you do choose the LED, which we recommend because of its efficiency, select one with adjustable settings.

Runtime Duration

We don’t recommend running your lights any less than the amount required for growing plants. This is usually an average of 12 hours per day. Some plants may only need about eight hours of “daytime” light. Others may require about 18 hours of it.

However, try not to “waste” energy by letting your lights run all night. You usually don’t need to. However, you may not want to stay up long enough to turn off your lights. If not, using a timer that automatically shuts them off helps. Newer indoor grow lighting systems provide this feature.

The Type of Light You Use

If you have the means for an LED grow light, start with that. It costs more upfront but will not heat up as hot, so it can provide you with more safety for your grow room. LED lights also radiate more light than they do the amount of heat they emit.

We do understand, however, that you may not have the funds just yet. Otherwise, you perhaps want to add some supplemental lighting, such as fluorescent ceiling tube lights. You can do that if you wish. Any amount of illumination for now will help.

Just so you know, the standard incandescent ones are probably one of the least efficient you can use. You also can’t place them as close to plants as other types of lights, although it’s best to keep all your plants at least one or two feet away from your lighting source–just to be safe.

Availability of Natural Light

Anytime you can take advantage of natural light to grow plants indoors, that will help. Even indirect light, such as what you might experience from the west or north side of a house, would help.

If anything, it may aid in nighttime light cycling, especially on a clear, starry night when the full moon is out. If you have plants you know need quite a bit of light, place them near a south window. If they can thrive in partial shade, perhaps near an east window is fine too.

Your Growing Objectives

Your plants will need more light from the time they shoot above the soil until they mature. The most crucial times are probably during the vegetative and flowering stages.

If you want to produce plants as fast as possible, you perhaps may alter the intensity of them. However, beware that too intense (or too bright) of light could burn your plants.

Be careful, but that’s what grow room testing is for. It will help you determine how intense you can set your lights for the speed you want them to grow.

When working on growing plants faster, you may want to research what the ideal light spectrum settings for your plants would be. Don’t go overboard though, or you might waste effort and money you don’t need to be wasting.

Sometimes, your growing objective may have more to do with improving plant quality. In this case, you might want to consider a light with a little more of a blue tint than usual. This will increase photosynthesis activation, and it could help you produce fuller sets of plant leaves.

On the other hand, a light with more of a red tint may increase budding and flowering success. Sometimes, you can turn up a single light wave higher within a full-spectrum lamp. This is one more way to achieve the optimal light spectrum for plant growth.

So what is the best light spectrum for plant growth?

Again, choosing the best light spectrum (optimal light spectrum) depends on a variety of factors. Plants usually make the most use of the visible light waves that range from about 400-700 nanometers (nm).

The blue hues of light waves typically range from about 400-490. The reds often start at about 700, but you may have some success turning up the temperature of red lights to 750nm.

Now, we do understand that what is optimal for plant growth may not be the best for your eyes. For that reason, we recommend a full-spectrum light that has dimming capabilities. Green light also is easier on the eyes, which allows you to tend to your plants while lamps are on.



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