Why are LED Grow Lights Purple? Do Plants Need Purple UV Light?

purple led lights

A Guide Through Uv Grow Lights

Growing plants at home are one of the best ways to ensure you get the best quality produce with minimal chemicals. However, growing them outside is impossible throughout the year, calling for indoor gardening.

One challenge, however, is providing the plants with the benefits they get from the sun, which is why you need to invest in grow light for UV light.

What Is UV Light?

UV (ultraviolet) light is a type of electromagnetic radiation from the sun transmitted at different frequencies and wavelengths. It is broken down into UVA, UVB, and UVC. While UVC does not naturally occur on earth because of the atmosphere, UVA and UVB play an essential role in different parts of our lives.

UVA is the most penetrative and abundant on earth and offers the most benefits for plants. While UVB is consumed mainly by our atmosphere to change oxygen to ozone, it is essential for plants because it helps improve color and protects them against microorganisms.


Do Plants Need UV Light?

When you use it in the right amounts and the correct way, UV light offers the following benefits to your plants.

  • Increases resins and oils
  • Reduces stretching and increases branching
  • Increases root mass
  • Increases plant potency
  • Improves smell and taste
  • Increases plants’ resistance to fungus, bacteria, and pests
  • Improves flower quality and weight

UV light also hastens the germination process when you grow your seedlings indoors. Moving the seedlings immediately from low-intensity light to strong-intensity light could result in shock, slowing down the growth.

When you move them outside, UV indoors prepares the seedlings for more intense light sources, making the transition smoother.

How To Introduce Grow Lights To Plants

Depending on the space and budget, there are different ways to incorporate UV light into your indoor growing space.

1. LED grow lights

This is one of the most popular and safe options for commercial or small-scale growers. One of the main benefits is that these lights convert approximately 90% of the energy into light, reducing heat emission. This makes them produce light that is closest to natural light.

This increases their effectiveness and reduces heat damage to plants. It also helps save energy and reduce your bills. They also play a massive role in increasing your yields because they use spectral tuning and are adjustable.

LED lights are also among the most durable options, reducing costs in the long run. You also don’t need to worry about exposing yourself or plants to toxic vapors.

2. Fluorescent lights

While they are less effective than LED lights, they are suitable for beginners because they are more affordable. They produce UV light through a chemical reaction activated by electric currents. However, most of this light is blocked by the bulb’s phosphorus coating.

Another significant thing to worry about when using fluorescent bulbs is exposure to mercury vapor when they break and the sharp pieces that can damage your plants and hurt you.

3. HID grow lights

High-Intensity Discharge grow lights are the most powerful. These lights are made with a glass tube that uses metal salts and gases to transmit electric currents between the tungsten electrodes.

While they produce a lot of helpful UV light, they also produce a lot of heat, which damages the plants if left on for too long.

Why are LED Grow Lights Purple?

Many people have started adopting indoor farming, and while you can use different LED colours, many people gravitate towards purple grow light. When choosing a color for your grow lights, consider the wavelength because the shorter it is, the more energy your plants get.

So why are grow lights purple? With a wavelength of between 380 and 450 nm, purple UV light has the shortest wavelength.

Another reason why you should use purple light for plants is that the purple spectrum is a combination of blue and red light spectra, colors that are key to solid plant growth.

Red has a wavelength of between 630 and 660 nm, and it is the primary color plants use stem elongation inhibition and photosynthesis. It also indicates to the plant that no plants are above them, signalling uninhibited development.

On the other hand, blue light, with a wavelength of 400-500 nm, stimulates stomatal opening, leaf expansion, stem elongation inhibition, photoperiodic flowering, and curvature towards the light.

While you can use blue and red lights separately, it will be more costly and consume more space than using a purple LED grow light. Also, purple lights for plants are more robust than the two individually, and research shows that plants exposed to purple light are richer in antioxidants.

Combining blue and red colors also ensures your plants have a circadian rhythm. This ensures the plants know when to rest and perk up, as they would if you planted them outdoors.

One of the main advantages of using purple LED grow lights is that you can adjust the level of blue and red light depending on your plants’ needs. The typical ratio for the two lights is 15 to 20 percent blue light and 80 to 85 percent red light.

They are also cheaper to manufacture, making them cheaper to buy than other lights like white.

When Should You Use Purple Grow Lights?

Blue light affects how plants produce chlorophyll and acquire nutrients. On the other hand, red lights stimulate the development of root systems, flowering, fruiting, seed germination, and photosynthesis, increasing the rate at which plants convert nutrients to chemicals they can use as food.

This means that plants require more red than blue light. However, if you are growing plants adapted to low-light conditions or want to plant them where there are fewer daylight hours, ensure to increase the blue light ratio.

Purple light is primarily beneficial for plants in the vegetative growth cycle. This is when the plants are producing the most leaves and stems.

Purple light plant growth differs depending on how much red or blue light your purple spectrum has. If you want smaller and more compact plants for smaller spaces, ensure you expose them to more blue light. However, dial the red light when it is time
for flowering and fruiting.

When germinating your seeds, it is best to ensure the purple light has a more red spectrum.

Which Plants Do Well Under Purple Uv Light?

Purple LED grow lights are best suited for plants that produce fruits and flowers instead of leafy ones. These include tomatoes, peas, beans, eggplants, squash, pepper, and cucumber.

Also, most of these plants require long sunlight days to produce high-quality and well-sized fruits. Whether you use purple LEDs or a purple light lamp, you can increase the amount of light your plants get by lighting them even at night.

Full Spectrum Led Grow Lights

While LED growing light purple color can sustain plants throughout their life cycle, you might want to include other colors throughout some development stages to help with quality and growth speed.

This means that you have to consider using a full-spectrum grow light. While many manufacturers use only red and blue diodes to achieve a purple spectrum, some include white and green diodes to make it full-spectrum, the closest to the one produced by the sun.

Full-spectrum lights affect the accumulation of compounds like phenolic, which help boost the flavor and smell of plants, plus their benefits to you.

Full-spectrum grow lights also make it easier to control your plants’ growth. If, for example, you want your plants to grow taller, you will increase the yellow, orange, green, and far-red colors, but if you want them to grow shorter and more compact, you increase the blue light.

These lights are also essential if you grow different plants in the same room, ensuring they all get maximum benefits.

Green grow lights, with a wavelength of 500-565 nm, offer significant benefits to plants because it promotes germination, leaf expansion rate, vegetation, stem elongation, and flowering. It does this by letting light reach lower branches of the plants that other lights would not have reached.

It is also beneficial for small plants unable to produce adequate chlorophyll amounts for proper germination. The green pigment helps increase chlorophyll, increasing the plants’ growth rate.

With a wavelength of 400-700 nm, white light is considered the least useful for indoor plants. However, it provides a range of colored lights for different pigments.

Distance Between The Plants And Lights

This is the most important thing to consider to ensure your plants get the right amount of light without excess heat that will cause bleaching. There is no exact answer to how high or low the lights should be.

It depends on the plants you are growing, the size of your space, and the types of light you use.

The higher the wattage of the lights you use, the further away they should be from your plants. Usually, you require 20 to 40 watts of power for every square foot. Therefore, low-wattage LEDs that produce approximately 200 watts should be between 12 and 20 inches from the plants’ tips.

However, if you use higher-wattage LEDs producing over 1,000 watts, you should have them between 36 and 46 inches away from the plants.

Medium-wattage purple lamps should be between these ranges. While this solution works for many lights, different styles like spider-style lights and science LEDs have different specifications indicated by manufacturers.

Ensure you monitor your plants closely and adjust the distance as they grow depending on their stage. Seedlings are the most vulnerable and sensitive. While you might be tempted to shed high-intensity light for a short period to stimulate growth, keeping the light above the canopy for the following wattages is best.

  • Up to 20 inches for 200W
  • Up to 27 inches for 400W
  • Up to 38 inches for 600W
  • Up to 42 inches for 800W
  • Up to 46 inches for 1000W and above

In the vegetative stage, the plants are still vulnerable but require more light for strong root development. This means you should regulate the proximity to the plants as follows.

  • Between 12 and 20 inches for 200W
  • Between 20 and 27 inches for 400W
  • Between 30 and 38 inches for 600W
  • Between 32 and 42 inches for 800W
  • Between 36 and 46 inches for 100W and above

The flowering stage is the plant’s final stage, requiring the highest light intensity to support stem growth, flowering, and fruiting. This means that you should move your light closer to your plants as follows.

  • Between 8 and 16 inches for 200W
  • Between 13 and 21 inches for 400W
  • Between 18 and 30 inches for 600W
  • Between 19 and 34 inches for 800W
  • Between 21 and 36 inches for 100W and above

To ensure your plants have a smooth transition between different stages and different light intensities, ensure you change the light distances gradually.

You should also monitor your plants for any signs of too much or too little light. Some signs of too much light include burning, bleaching, and stunted or irregular growth. This causes your plants to have brown outlines along the leaves, yellow and white spots, and curly, limp, or droopy leaves.

With little light, your plants will look weak and stretched. Since the plants grow exceedingly long trying to reach for the light, you might confuse this with accelerated growth. However, if you don’t correct it soon, it could result in death or stunted growth.

Things To Know Before Buying Grow Lights

Getting your grow lights is the first step of the process, but there are more things you must consider to ensure your plants’ health and safety.
Before you buy your grow lights, here are the things you should consider.

1. Plant requirements

Knowing whether your plants need to grow tall, develop more branches, become bushy, or produce flowers or fruits will help you choose the right type and color of LED grow light.

2. Space limitations

Purple grow lights come in different styles like purple lamps and purple LEDs, suitable for different spaces. Before planting, ensure your planting space has the proper ventilation, filters, fans, and tents. This ensures there is ample air exchange from the plants and outdoors, reducing plant toxicity.

It also ensures your plants are safe from extreme weather conditions like snow, wind, and heavy rains, ensuring you get a good harvest, plus pests like rodents, ants, spider mites, and aphids.

3. Cost

LED lights are usually expensive to buy and install. However, they are the most durable and require the least maintenance, making their long-run costs lower than other lights.

Before buying your purple LED lights, research and compare different sellers to get the best price. While getting the cheapest sounds like the best deal, ensure you look at the quality and brand to ensure you get your money’s worth.

4. Safety precautions

While UV light has numerous benefits for you and your plants, too much exposure could cause damage to the plants and hurt you.


Whether you are growing plants for commercial purposes or domestic use, having the right equipment will ensure high-quality and quantity production. The most important thing to consider when planting indoors is to grow lights.

These ensure that your plants get the UV they would have if you planted them outside. They are more beneficial than outdoor planting because they allow you to control how much light your plants get at certain times and stages.

While there are many colored grow lights, purple grow lights have become increasingly popular because they combine the advantages of blue and red lights. These are the most important for flowering, fruiting, and proper root development.
Before buying the lights, however, ensure you research everything that goes into using purple LED grow lights and how you can maximize your yield.

Ask for advice from experts or other people using purple light for plants. This gives you an insight into what to expect and what you can do differently for better results.


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