Purple LED Lights in Vertical Farming: Why Does Light Color Matter?

Purple lighting is getting a lot of attention in the vertical farming industry. Substantial plant growth, cheapness, low power usage, and low heat generation are just some of the benefits this technology presents. This article will discuss the importance of purple light for plant development, its power usage, and heat emission.

Purple LEDs are more cost-effective than any other artificial light source used in vertical farming while providing equal or better results. Purple lighting provides the plants with wavelengths needed for photosynthesis, growth, and flower formation.

Are you interested in finding out how purple light influences plant growth? If you want to know more about the electricity usage or heat emission of purple LEDs in modern vertical farming, keep on reading, and you will find answers to these and a few more questions.

Why Is the Light Color Purple?

Purple color boosts the plant’s growths, increasing it where it’s needed. It provides the plant with a mixture of blue and red lights while avoiding excessive lighting the rest of the plant. We need to first discuss how and why purple LED lights work to understand their benefits.

Plants ‘see’ a lot wider spectra of colors than humans do. They use wavelengths from the hyperspectral range, including ultraviolet and infrared spectrum, in addition to the ones seen by people. Studies show that the most important colors for plant development are blue and red. And guess which color you will get when you mix blue with red? You are right! Purple!

You can find blue at the beginning of the visible spectra at the wavelengths from 450 to 495 nm (nanometers). Red is at the very end of the same spectra, between 620 and 750 nm. These regions of the spectra are called Photosynthetically active radiation (PAR). By taking one blue and one red LED, their colors combine and emit purple light. When speaking plant language, we can safely say that our purple translates to blue-red for them.

Purple light LEDs are produced straightforwardly. Blue monochromatic LED chips radiate light onto red phosphor, which combined produce a purple light. Those are high-powered LEDs used for brighter light output. An alternative is to use only blue and red bulbs, one next to another, on a LED strip. These would be low-powered LEDs, mostly used as indicators or in smaller farming facilities.


Best Light Spectrum for Plants Growth.

When I say that the plants love the Sun, what I mean is that they enjoy only some distinct wavelengths. The human eye can only perceive the sunlight as white-yellow rays, but it’s a rave-party in the plant world. Sunlight provides the plants with a plate full of ‘light’ food, but they’re picky eaters. Their favorite colors are blue and red, and there are many reasons why.

Both blue and red colors are vital for photosynthesis. Chlorophyll, light-absorbing bodies in green parts of the plant, suck up these colors and deflect green wavelengths. We discern green color because it bounces off of a surface and returns to our eyes.

Blue color has a shorter wavelength than red. It also has a higher frequency which means it also carries more energy. It’s important in the process of photosynthesis, but most of all, it is needed for growth regulation. Green plant organs, like stems and leaves, grow thicker, shorter, and greener when exposed to more blue light. These traits are desirable when it comes to the production of houseplants, especially ornamental pot plants. You can control the growth of your plants by selectively shining a blue light on the particular parts of the plant.

On the other hand, the red color has a longer wavelength, a lower frequency, and carries less energy than blue. This energy allows the plant to grow flowers and strengthen the stems responsible for fruit-carrying. It also increases the effectiveness of photosynthesis, which allows better sunlight-to-energy conversion in chlorophyll. In contrast to blue color, red bolsters the organ growth, which makes leaves thinner and larger, which increases the plant in length.

By combining red and blue into purple color, plants get all the necessary light they need for healthy growth.

It’s important to differentiate between purple LEDs and ultraviolet lamps. First off, purple and ultraviolet are not the same color. As mentioned before, we could define purple as blue-red, peaking at 450 and 660 nm. Ultraviolet is a color in the spectra of 255 to 420 nm, which we can’t even see. Purple LEDs are much safer than UV lamps and provide the plant with all the indispensable light.

Grow Lights Color vs. Electricity Used

LED lights generally use very little electricity. They are extremely efficient for their cost and require minimal space, which makes them perfect in vertical farming.

Now, you may ask yourself, how is it possible? Well, an LED bulb contains a simple transistor or semiconductor. Essentially, it’s a tiny electric circuit that doesn’t use any additional means to produce light. A semiconductor consists of two separate plates facing one another. There’s a small gap between the plates, which means they’re never touching. When the electricity surges through the circuit, it causes the energy to jump from one plate to another. Any excess energy is then emitted as light.

Power consumption depends on the light color. Red light needs less electricity to excite photons than blue light, which in comparison, uses 6% more electric current to emit light of the same intensity as red LEDs. But in general, you can conclude that electricity consumption by LEDs is incredibly low.

Purple LEDs consist of 75% red and 25% blue diodes. The more red lights an LED has, the less power is needed to light it up, which means that purple lights are highly efficient when converting electricity into light.

Now let’s look at other light colors and their electricity consumption.

One option is to use green and yellow bulbs. Both of these colors have a higher frequency than red, so they need more electricity to shine.

Another option is white LEDs, which are often used as artificial light sources because they’re more appealing to the human eye. They consist of red, green, and blue bulbs (sometimes yellow too) connected in a series. They need the power to light all three RGB bulbs to achieve white color, which means they need a lot of energy.

Some gardeners use red, green, and blue (RGB) diodes for better growth, but they disconnect the green ones. The result is a purple light. Also, you can buy LED strips with only red and blue diodes. In the first case, purple light uses only 2/3 of the energy otherwise used for powering the entire RGB LED.

High-power phosphorous LEDs use 10 times the power of low-powered LEDs. However, they’re driven by a higher current, too, while providing 200 more lumens of light at once.

Grow Lights Color vs. Heat Generated

LEDs are well known for not producing too much heat. Purple, or blue-red ones, are no exception. In general, light sources that don’t produce infrared radiated (IR) light don’t heat their surroundings by much. For example, incandescent bulbs use 83% of the power to produce IR light, making them hot on touch.

Surprisingly, LEDs convert only 20 to 30% of the power into light, with the rest of the energy being transformed into heat.

Most LEDs don’t use any type of cooling device, so they release their heat passively via convection. Low-power LEDs naturally output low amounts of warmth around themselves. Heat sinks in the LEDs’ components, and the air around the surface of the light, so dissipates quickly.

The thing is, LEDs are produced in such a way that excessive heat damages affect the junction in the bulb. By raising the current, you also raise the temperature in the junction, which decreases the effectiveness of your lights. It sounds a bit oxymoronic that a higher current lowers the light discharge, but it’s more of a heat problem than anything else.

Red bulbs produce the most amount of heat in purple LEDs. They’re more tolerant to increased current, therefore temperature too, compared to the blue ones. Purple LEDs produce the combined heat of blue and red lights. The spacing between LEDs in an array causes a portion of the heat to fall off. In the end, it’s still very minimal, so you shouldn’t be afraid of purple lights burning your plants.

White LEDs generate more heat than purple ones, but they mostly come with a copper or aluminum heat sinks. These materials conduct temperature more efficiently, so you won’t notice the excessive amount of heat. On the downside, they’re expensive and are used only for high-power white LEDs. Again, heat is connected directly to the current passing through the LED. White ones use more bulbs, have more junctions, and produce more warmth compared to purple LEDs.

An array of high-powered purple LEDs produces a lot more heat. Using an external water cooling system is advised in vertical-farming. There are alternative solutions to heat problems, and one of them is using a controllable voltage. This way, you can alternate between low and high voltage, reduce overall heat, and still grow strong and healthy plants.


Purple LEDs are very commonly used in vertical farming nowadays. Purple light is a result of combining blue and red wavelengths.

Blue lights benefit the development of chlorophyll, make the stems and leaves shorter but thicker. Red color induces vertical growth and makes the fruit-bearing organ stronger.

Newer technology includes using blue background light strips that heat red phosphor, and the result is a mild purple color.

Purple LEDs are great for vertical farming because they’re cheaper, more effective, and more durable than any concurrent light technology.

Mateusz Piechowiak

In 2019 I stumbled upon the concept of vertical farming and since then it became my passion. I built in my home my own mini vertical farm to have access to fresh homegrown vegetables as well as to explore the subject of growing in a controlled environment. My goal is to spread the idea of vertical farms because I strongly believe that they can change the world for the better.

Recent Posts