What Type of Light do Plants Prefer?

Russian botanist Andrei Famintsyn first used artificial lighting for plant growth in 1868. Nearly 10 years later, he published his first Russian textbook about plant physiology, with a particular focus on plant metabolism and photosynthesis. His research paved the way for a new approach to agriculture.

After Famintsyn’s work was publicized, agriculturalists recognized this potential for growing their crops indoors. Artificial lighting empowers individual growers to tailor crops to their specific needs, regardless of season or weather conditions — a revolutionary accomplishment in human history. However, as growers both past and present have realized, lighting indoor plants is more complex than one might initially believe.

The timeless question persists: What light do plants best respond to?

Not All Light is Created Equal

Firstly, plants need some sort of light, period. Without ample exposure to a light source, plants aren’t able to accomplish photosynthesis — the process by which plants convert light energy into chemical energy.

However, not all light is usable by plants — this is important for any cultivator to take into consideration when choosing grow lights. The amount of available light that is usable by plants is most often referred to as Photosynthetically Active Radiation (PAR). According to our recent blog post discussing on uniformity, “PAR is sometimes misunderstood as a measurement, such as kilos or ounces. Rather, it is the type of light that is possible for plants to absorb for photosynthesis. This light is actualized in wavelengths seen between 400 to 700 nanometers.”

There are slight variances depending on the specific crop species. Depending on the type of plant, some may prefer direct light while others do best with some shade. Some require hours of darkness, others do best with lots of bright light. These settings may also be influenced by the individual plant’s stage of growth, whether it is a seedling or ready to flower. It’s best to understand the particular evolutionary needs of the crop before switching the lights on.

Over the Rainbow: How the Color Spectrum Impacts Your Grow

One may assume that the best lights are ones that most accurately replicate natural sunlight. To an extent, this is true: natural sunlight delivers the full spectrum of color, offering a whole host of benefits to a growing plant. However, as long as people have practiced agriculture, they have noticed the subtle differences with different kinds of light. This is illustrated by the way seedlings elongate in dimmer light, or how quickly a plant flowers. The physical responses of plants to different types of light is called photomorphogenesis.

Plants typically respond most to red, far-red and blue light. This is because of a collection of light receptors found within the biology of plants deemed phytochromes and cryptochromes. These receptors encourage the release of growth hormones. While red and blue light have received the most attention in the growing community, it’s also important to recognize the benefits of green light.

According to research initiated by NASA, LED lights are able to offer the most accurate full spectrum for indoor grow facilities. The lighting technology offered by LED bulbs is able to offer these red and blue light wavelengths, while not forgoing the green and yellow aspects of the spectrum. This research led scientists to install LED lights on the International Space Station. There, astronauts are able to cultivate cabbage and some flowering plants, such as zinnias. Their basic findings are summarized here:

  • Red light (630-660nm): Red light wavelengths helps deliver dormancy, germination and flowering in a plant. A grower seeking fast growth and ample harvests would primarily utilize red light.
  • Blue light (400-520nm): While this light should be mixed with other spectrums to prevent stunting a plant’s growth, blue light wavelengths can assist in developing leaf thickness and chlorophyll production.
  • Green light (500-600nm): Green light has proven to be helpful particularly when attending to a dense canopy. Green light is able to penetrate the lower levels of the canopy, whereas blue and red light may only be beneficial on the surface.
  • Far red Light (720-740nm): Like blue light, far red wavelengths are also able to penetrate a dense canopy, ensuring smaller plants receive much-needed light. Far red light has been utilized for its ability to encourage flowering early on.

To conclude, our initial question — what kind of light plants like best — is not easily answerable. There are several considerations when deciding what lights are best for your facility: What is your ultimate goal? Some growers want to have a large harvest in a short period of time. Others may prioritize potency or aroma.

As NASA research has shown and the growing community has confirmed, full spectrum LED lights are the best option for delivering the highest quality light for any type of indoor crop.