Light Spectrum Effect on Each Stage of Plant Growth and Development

LED lights for plant growth.
Grow lights have become commonplace for use in indoor gardening. You have quite a few options when setting up your interior growing environment if you haven’t already.

If you have experience using grow lights to produce indoor plants, then you’re ahead of the game. If you’re new at this, you need to learn how to yield a successful indoor harvest. This requires understanding the light spectrum and the effect of light on plant growth and development.

Before we explain the light spectrum effect on plant growth, we will introduce a summary of the plant life cycle. If you understand the plant life cycle, you’ll know what we’re talking about when we mention the plant growth stages in relation to the light spectrum effect.

Summary of the Plant Life Cycle and Growth Stages

We compiled a complete summary of the plant life cycle using the information that Galveston Bay, individual growers, and major suppliers provide. It’s also a list of the terms we decided to use to teach you the plant growth stages.

The terms we use for this plant growth stages summary coincide with what we want to teach you about the effect of light on plant growth and development.


The beginning stages of germination happen when a seed begins to grow beneath the ground. It occurs right before or during the time when a plant begins to sprout.


Sprouting begins the transition between the germination and seedling stages. During the sprouting stage, a plant begins to grow at least one stem and some leaves. You will first notice the sprouts when they emerge from the soil’s surface.


During the seedling phase, a plant has become a mature sprout. It’s still a young plant though. It hasn’t become the vegetative process of preparing to bear fruit yet.


The time between germination and flowering is the vegetative plant growth stage. It’s like being an adolescent if a vegetative plant was a human. The vegetative plant is “almost an adult.”

At this growing stage, the vegetative plant is preparing for budding and flowering. You will notice crops growing taller and perhaps branching out more. They may appear wider than they were at the sprouting and seedling stages, but they have a ways to go before they reach maturity.


During the budding stages, you’ll notice little nobs on the stems. Later, those buds blossom into flowers. The plants may still grow higher and spread out more during this phase and reach near their maximum height and width than they would during the vegetative stage.


The buds on your ripened plants have already turned into flowers. For some crops, these flowers ripen into fruit before they fall off the stem. For other crops, the ripened stage calls for the flowers to drop their seeds to start the plant growth cycle all over again.

Some mature plants will lose their leaves and grow dormant. During the winter, that’s when they would usually show just bare stems coming up from the ground. That pertains to growing outside, however.

If handling mature plants indoors, you might take some of the offshoots from the flowering plants. Those you can transplant and discard the others that may no longer reproduce.

What is the light spectrum effect?

When we speak of the “light spectrum effect,” we mean how plants react to specific light waves present in grow lamps. You can either use the full-spectrum grow lamps for your plants for all stages. Otherwise, you can choose single light waves for specific growth stages.

The Light Spectrum Explained

When answering the question about the light spectrum effect, we realize you may need more information. The light spectrum is the seven visible colors of the rainbow found also in artificial grow lights, such as LED, fluorescent, high-pressure sodium, incandescent or other types.

Some lights on the market provide specific colors for your plants. For instance, you might find some LED lamps that only emit red or blue lights. Others may have white lights built into them. If you use the white lights for your plants, that signifies a full spectrum with all the rainbow light waves.

In case you need a review, the seven light wave colors in white light are these: red, orange, yellow, green, blue, indigo and violet. These colors present in white light make up the full light spectrum, all of which can have a positive effect on plants. Most of the time, however, growers usually choose between the red or blue lights and the full-spectrum lights.

Ideal Light Spectrum Based on Growth Stages

Most plants use the light waves from violet to red in the light spectrum. This ranges from 400-700 nanometers, with the cooler colors of blue and violet on the lower end. The red is on the opposite end of the light spectrum for plants.

Ideal Light Spectrum For Seedling Stage

Most sources recommend a blue light spectrum for seedling plants. This typically ranges from 450-490 nanometers on the light spectrum effect scale. Some seedlings you grow might also do well in the blue-green spectrum of a little bit above 490 nanometers.

Ideal Light Spectrum For Vegetative Stage

You can continue with using the blue light spectrum for the vegetative stage growing periods. However, you may want to start adjusting the light spectrum for veg stage settings once you see the plants have grown buds.

Ideal Light Spectrum For Flowering Stage

The ideal light spectrum for flowering stage growing periods usually is red. This usually measures from 600-700 nanometers. You may want to set this light spectrum for your flowering plants when the buds first start to blossom.

Do all lights have the same spectrum effect?

The spectrum effect on plants varies. Some grow lamps are engineered to only provide a single color, usually red or blue.

Others might provide the green light, which acts as a neutral color that’s easy on the human eyes and useful during plant maintenance sessions. Some lights provide every light wave on the spectrum, which offers a different effect than just a single light wave lamp. The light spectrum effect that a lamp can have also is different for fixed versus variable spectrum lights.

Fixed Versus Variable Spectrum Lights

Some grow lights only radiate a limited range of light waves. For those, you can’t change the color concentrations. You’re also committed to just one intensity for each light your lamps radiate. You might hear them referred to as “fix-spectrum lighting.”

Certain types of full-spectrum lighting, which does offer all seven visible light waves, may also only have fixed-spectrum light settings. You can’t change the concentrations of the colors, and you can’t change the overall brightness of your lamps either.

Other lights offer variable spectrums. This means you can adjust the temperatures, concentrations, brightness or intensities of your grow lights. This includes adjustments you can make within full-spectrum lights when you want more blue or more red for your plants.

What is the best light spectrum for plant growth?

If you try to control too many variables of your indoor garden, it may fail. When starting out, it’s best not to overthink what is the best light spectrum for plant growth.

We recommend that new growers use a full-spectrum light for plant growth. This ensures that your crops receive at least some of what they need. They should at least grow at a moderate pace if you leave your lamps at the recommended factory settings.

When choosing the best light spectrum for plant growth, consider light waves between 400-700 nanometers. Any LED white light will surely provide this, and we recommend this type of light the most.

Why do you recommend LED grow lights?

Why do we recommend LED grow lights? It’s because they usually provide the most efficiency and don’t burn as hot as fluorescent, or incandescent lights. It also runs safer than some of the HID lights you may have heard of out there.

What other lights can you use to grow plants?

All types of indoor grow lights have a different light spectrum effect on plants. You can experience some growing success using just about any light.

Even a standard incandescent household light can work in a pinch. the problem with this type is that its efficiency ratio is typically 10% light to about 90% heat.

Fluorescent lights, on the other hand, do provide almost as well of an efficiency rating as LED lights. The major issue is that they sometimes run almost as hot as the incandescent ones.

By the way, high-pressure sodium (HPS) and metal halide (MH) lights also can make plants grow. They even sometimes have a similar effect of light on plant growth and development as the LED growing lamps.

One issue with HPS and MH is that they’re also prone to accidental fires. It’s not that you can’t start a fire with an LED lamp, but the HPS and MH bulbs could break easily and start a blaze. When in doubt, stick with the LED if at all possible.


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