Why Are Grow Lights Purple?

As a beginner who has never experienced grow lights, you will surely have some questions about the features and functionality of this artificial lighting system. One of the popular questions people have is, “why are grow lights purple?”

I wouldn’t say the illumination produced by LED grow lights is mainly purple. It is in the purple spectrum of color the light produced is typically perceived. Natural light from the sun contains all frequencies of color that are needed for healthy growth and good yield. Nevertheless, the light appears white.

However, in most LED grow lights, the particular spectra of color needed by plants the most for photosynthesis is what manufacturers focus on. That is the red and blue light that combines to produce a seemingly purple color. If you have also been wondering why these lights typically give out the purple color, I will explain the answer in this article.

Colors That Plants Need?

Several beliefs hold ground concerning the light colors that plants need for healthy growth. The most accepted seems to be that red and blue lights are sufficient for healthy plant development. However, that is only true to an extent.

While the red and blue lights are among the most important colors needed for photosynthesis, there are several other essential colors necessary for plant development. The distinguishing factor is the quantity of each wavelength required by plants.

Research by NASA established that LED lights offer the most optimal lighting for plants, of all types of grow lights. Other findings also determined the effect of different light wavelengths and how much the plants need them.

  • Red light (630 – 660 nm)
    Needed for seed germination, flowering, and dormancy period sustenance. Likewise, this wavelength helps with the growth of stems and the expansion of leaves
  • Blue Light (400 – 520 nm)
    The blue light has to combine with light in other spectra to prevent stunted growth because overexpsosure to this particular wavelength can cause it in some plants. In addition to influencing chlorophyll, the light is also responsible for leaf thickness.
  • Green Light (500 – 600 nm)
    This is another spectrum that is important to plants. It used to be a widespread belief that this wavelength was not necessary for plants. However, with indoor gardening becoming more popular, this wavelength can penetrate thick canopies to support leaves at lower levels.

Why LED Grow Lights Are Purple?

While light from LED grow lights typically appear purple to the human eye, they typically produce lights in several spectra. Nevertheless, blue and red lights are popularly regarded as the most significant in photosynthesis.

Red is responsible for photosynthesis and stem elongation inhibition. And blue light controls leaf expansion, stem elongation inhibition, stomata opening, photoperiodic flowering, and more.

The significance of the red and blue light in plant development is what has influenced the design of LED grow lights to include red and blue diodes majorly. A combination of red and blue diodes is responsible for the seemingly purple color that LED grow lights emit.

Most of the grow lights that dominate the market today have more than just the red and blue diodes, but they still produce purplish light due to the dominance of the red and blue diodes.

More than the functionality of red and blue diodes, these grow lights typically give out purple light because the red and blue diodes they come with are cheaper to make than other diode colors. So, manufacturers include more red and blue diodes, and in some cases, there is a significantly lesser quantity of white diodes.

Interestingly, red and blue diodes partly influence the energy efficiency of LED grow lights. The plants absorb all the wavelengths produced. The white diode, for example, produces yellow, green, and other wavelengths that are not critical for plant development.

Is Purple Light Effective?

The effectiveness of the different light spectra can be vague, with no specific measurement standard that is commonly accepted. However, there are specific indications that that inform prevailing beliefs.

Firstly, purple LED lights are effective; they perform well at the vegetative and flowering stage. However, some confusion exists as to whether the combination of blue and red lights is enough for plant development.

The specific wavelengths required for plant growth can be found among those produced by red and blue bulbs. This implies that the purple light is sufficient for plant development in typical cases.

However, the ratio of red to blue diodes in a grow light is also critical. This is why it is essential to know how exactly plants are affected by different wavelengths. If you want taller plants, for example, you need more blue diodes in your light that red.

On the other hand, if you want more leaves and better buds, more of the red wavelength is what the plants need. All in all, the purple light from LEDs, produced from a combination of red and blue bulbs, is effective for indoor gardening. Still, for additional benefits, you can also consider other spectra.

What about White Light?

Lighting from the sun is categorized as white light, and it contains all frequencies of light that can be seen with the naked eyes. This is why sunlight is still regarded as the best form of lighting for plants. Plants are typically able to utilize whatever wavelengths they need, from the full spectrum light provided.

However, in artificial lighting, a white light would contain the red and blue wavelengths needed for photosynthesis and green, yellow, and other wavelengths. As plants mostly absorb red and blue wavelengths, a lot of the different wavelengths contained in white light would only go to waste.

With sunlight, you don’t have to worry about energy waste, because the source is everlasting. However, it would help if you considered energy efficiency with grow lights. This is one of the reasons why LED grow lights majorly feature red and blue bulbs, with a low number of white diodes at times.


If you have ever wondered why a lot of the LED grow lights on the markets produce purplish light, it is simply as a result of the dominance of red and blue diodes in the lights. While the red and blue wavelengths are the most essential for plant development, it wouldn’t hurt for your plants to enjoy some benefits of other wavelengths. So, if you can afford to go for “full-spectrum” grow lights, you should go for them. Also, with these purple lights, you have to wear protective glasses, because they can be harmful to the eyes.

I sincerely hope you’ve found this article helpful. Do share with your friends, family, and other indoor gardening enthusiasts. Feel free to share your thoughts in the comment section below.

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