Why Are Some LED Grow Lights Purple?

why are some led grow lights purple

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LED grow lights have many advantages for indoor plants cultivation. You can get fast and healthy plant growth similar to or even better than plants under sunlight. But why are LED grow lights purple in color?

LED lights are actually not purple, but it appears purple in human eyes. They seem purple because of the mixture of blue and red wavelengths. Blue and red wavelengths enhance the light absorption by chlorophyll for photosynthesis. These lights are also low-in-cost, efficient, and versatile for your indoor plantation. 

This article will discuss the reasons behind purple LED grow light. Let’s dive deep!

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What Is Color Spectrum?

The color spectrum is also called the visible spectrum. It means a range of the different colors produced when light expires through the glass prism. Certainly, the electromagnetic radiation is very light, and we can only see a small portion of the radiation.

The visible color spectrums are from red to blue and violet tones, with wavelengths within 450 – 700 nm. It means that all lights have a color spectrum. Some light sources have all the colors, while others have only some colors. 

Sunlight has all the colors mixed; hence it looks white or color-free to humans. It provides all the sufficient nutrients that plants need too.

For plant cultivation, different light spectrums will have varying impacts on the UV light absorption by plants. It is crucial to use the right LED grow light with suitable color spectrums to yield higher quality and quantity of crops. 

Before we learn further, you can read at this link to learn How LED Grow Light Works.

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What is the Relationship of Wavelengths and Colors?

The LED grow light manufacturers will make LED grow lights with specific wavelengths. The purpose is to create lights that are beneficial for your indoor plants. They also try not to make harmful or less beneficial wavelengths for your plants.

There is a nanometer range for each light wavelength that produces different light colors.

ColorWavelength (nanometer)
Blue Light400 – 500 nm
Red Light620 – 750 nm
Ultraviolet A320 – 400 nm
Ultraviolet B290 – 320 nm
Ultraviolet C100 – 290 nm
Infrared700 – 1,050 nm

The Functions of Purple Color LED Grow Lights 

The plants will respond to external stimuli such as light, weather, and others. The response of plants, positive or negative, will affect plants’ growth. 

In the case of light, different colors of LED grow light will influence the health of plants. But, what color of the light spectrum do different plants need in each growth stage? Does it have to be purple?

Let’s discover further about the effect of light colors on indoor plants.

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The Function of Red Light from LED Grow Lights

Red LED grow light is most important for plant growth and development. It can produce from 0 – 100% proportion of photosynthetically active wavebands similar to sunlight. Let’s look at the functions of red light from LED grow lights.

The red color from LED grow lights drive photosynthesis and promote plant growth better. In other words, it has the highest efficiency in transforming electricity to photosynthetic photons

It is because red lights are often absorbed more strongly by the chlorophylls, the green pigment in your plants. 

Besides, red lights are also essential for stem growth and leaf expansion. You can use them to promote or inhibit stem stretch. They can also produce thinner leaves and bigger and taller plants. 

But, you must control the red light as too many red lights will cause the plants to be too tall and spindly.

Red lights from LED grow lights can also affect the plant flowering. The red light of 1 μmol could restrain the flowering of short-day plants like violet at night. In contrast, you can use the same amount of red light to enhance the flowering of long-day plants like coneflower.

Moreover, the light of red will let plants grow up healthy as it will signal to the plants that there are no other plants so they can have free growth.

To sum up, red light is less costly and more efficient for your indoor plants. 

why are some led grow lights purple

The Function of Blue Light from LED Grow Lights

Most people assume blue lights are those with short wavelengths of 400 – 425nm. Thus, many think it is less effective than the green color wavelength. But, blue light can actually generate a similar effect as green or red lights to enhance photosynthesis.

In general, blue light produces a 400 – 500nm visible spectrum wavelength. These blue lights provide high energy and better effects for plant development and flowering.

Blue color LED light will also control the plant stomatal opening. It is crucial as it regulates the loss of water and intake of carbon dioxide for the plants. 

Besides, the blue color from LED grow light will inhibit stem elongation. You’ll find it beneficial to grow short plants, especially foliage plants.

Moreover, light in the blue range also affects the thickness of the leaf and chlorophyll content present. You’ll be able to produce plants with thicker, larger, and darker green leaves for your needs.

Blue wavelengths will also affect the leaf coloration. For example, your indoor plants with purplish leaves like Forest Pansy need blue color radiation. Otherwise, it might produce green leaves without blue lights.

In contrast, leafy greens like kale and broccoli will produce more healthful nutrition with sufficient blue lights. For instance, nutrition like vitamins or antioxidants.

Not only that, your indoor plants will be healthier with sufficient blue lights. For instance, The nightshade family plants like eggplants might get physiological disorders like small blisters on petioles, leaves, and stems without blue light. 

You can also use blue light to control the flowering of plants. High-intensity light at 20 μmol can cultivate flowering for long-day plants like spinach. It can also restrain flowering for short-day plants like a chrysanthemum.

In short, blue light from LED grow lights are affordable, efficient, and multifunctional. But, you must be careful when using it. You must not look directly at blue LED lights without UV protection glasses. Besides, overexposure to the plants will also affect plant species. You can learn more about How to Use LED Grow Lights for Indoor Plants at this link. 

Combination of Blue and Red Lights

During production, LED grow light manufacturers do not use pure white light that contains all wavelengths. It is because plants do not absorb all lights equally. You’ll get the most out of your LED grow lights if manufacturers choose the right light color in making them. Botanists can also save much electricity by using a suitable LED grow light.

We can see from the above that red and blue lights are essential colors for your LED grow lights. When combined, they generate purple color, which is commonly seen in LED grow lights.

Among all, yellow and green colors are the least absorbed. Plants reflect these lights and hence appear green in color.

After choosing the suitable LED grow light for your indoor plants, you must also note the distance to place them and ways to use them to generate the best output. 

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Advantages Of Purple Color LED Grow Lights

The right LED light color is the key to healthy plant growth. Now, let’s look at the benefits of purple color LED grow light. 

The purple LED grow light is versatile by providing the light needed for all growth stages. The blue light will enhance the growth and development and growth of plants. At the same time, red lights promote flowering and photosynthesis. Besides, the lighter and darker purple color will provide different benefits for your indoor plants.

Your indoor plants can also have a better routine for their day and night cycles. It is like how plants grow under sunlight.

LED grow lights manufacturers often build LED grow lights by focusing on blue and red lights combination. Your plants get the lights they need for healthy growth. Also, it prevents the wastage of unnecessary lights.

Lastly, the purple LED light provides more energy than another color.

From the information above, we know that LED grow lights are excellent tools for plant growth and development. You should not use regular LED lights as LED grow lights as these lights are specially designed for plants.

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Light Colors Needed by Plants on Different Growth Stage 

Do you know the light colors your plant requires at its particular growth stage? Let’s dive deep.

Germination and Seedling Stage

Plants need an intense concentration of blue light at this stage to allow compact growth. It is for the sprouting and growing of strong roots. 

Cannabis will need a certain percentage of 660 nm to 730nm of red and far-red lights to grow strong roots. You can also visit this link to learn more about cannabis lights.

Vegetation Stage

Purple light contains a shorter wavelength and produces more energy. It is ideal for indoor plants’ growth and development during the leafy vegetation stage. 

Red light is equally important during the plants’ vegetation phase. It will enhance hormone production to deter chlorophyll disintegration. As a result, your plants are taller and produce more nutrients. You can also get bigger leaves with more red lights and fewer blue lights.

In fact, red light is vital for cannabis to grow taller with lesser leaf nodes. You can adjust the red and far-red light ratio to achieve the optimum height and leaf percentage for your cannabis.

The plants will absorb certain green light during the photosynthesis process to grow taller and produce fruit. Though most green light is the least efficient wavelength for photosynthesis, it is the most useful in regulating plants. They will also reflect many green lights and hence look green in color. 

Flowering Stage

You should provide a combination of all wavelengths during the blooming stage of your plants. 

But, you should reduce blue lights during the late flowering stage of cannabis for better harvesting.

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Final Thoughts 

LED grow lights are famous for energy-efficient lighting and long-lasting. It has features such as a built-in heat sink to improve brightness and longevity. Although the price is higher than fluorescent light, you save much more operating costs in the long run.

Remember to inspect the quality and brand of the LED grow lights before purchasing. Other factors like warranty, heat sink, and certificates are equally important. You can also refer to our articles to learn the Top 11 Things to Consider When Purchasing LED Grow Light.

I hope this article answers your question about “why is LED grow lights purple.” If you are new to LED grow lights, you can seek free consultation from Darkless LED. We have over 20 years of experience in providing professional LED lighting solutions for worldwide customers.

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