Nowadays, LED grow lights have become an essential tool for ensuring healthy and robust plants. These lights offer the necessary spectrum for plants, enabling gardeners to cultivate vibrant plants throughout the year. However, understanding the right light spectrum for plants and its impact on their growth can be challenging and confusing. This guide aims to equip you with a comprehensive understanding of light spectra. So, let’s explore the fascinating world of light spectra!
What Is Light Spectra?
Light consists of various forms of electromagnetic radiation, but not all of it is visible to the human eye. Our eyes can only perceive light within a specific range of wavelengths. We have cone-shaped cells that act as receptors for certain wavelengths, primarily in the green, yellow, and orange spectra. This is why artificial lighting designed for humans has focused on these spectra and is measured in lumens.
However, plants respond differently to light spectra. While they do utilize energy from the middle spectra, they are more affected by the red and blue spectra. There are specific peaks in red and blue light that are crucial for photosynthesis, where most of the plant’s growth occurs. By adjusting the ratio of red to blue light, significant changes in plant growth can be achieved.
Additionally, there are invisible light spectra, such as ultraviolet light and infrared light, that can also affect plant growth. This is why LED lights have gained popularity in indoor gardening. LED systems with adjustable spectra allow growers to expose their plants to a specific light. This not only contributes to healthy plant growth but also allows growers to customize the desired outcomes. Different light spectra have a profound impact on plant growth, and LED lights enable growers to harness these effects effectively.
Do Plants Utilize All Light Spectra Emitted by the Sun?
Plant growers often believe that the ideal grow lights should mimic the light spectrum of the sun, which encompasses a relatively full spectrum across visible light frequencies. This belief stems from the fact that plants have evolved over millions of years to effectively transform light energy into carbs and sugars. The sun predominantly emits light in the middle spectra, which appear green, yellow, and orange to our eyes. These spectra are the primary frequencies that human eyes utilize.
However, studies have shown that these middle spectra are actually the least utilized by plants for photosynthesis. Instead, most photosynthetic activity in plants occurs in blue and red light. This is why plants benefit greatly from full-spectrum LED grow lights.
The counter-intuitive use of light by plants can be attributed to the evolution of photosynthesis in early forms of bacteria. Prior to the emergence of more complex leafy plants, photosynthesis is conducted in bacteria in the primordial sea millions of years ago. The yellow, green, and orange middle wavelengths were heavily used by these early photosynthetic bacteria for photosynthesis, which caused these spectra to be filtered out for plants growing at lower levels in the ocean. The non-filtered spectra, primarily in the red and green frequencies, that were not utilized by bacteria were all that remained as more complex plants evolved at lower levels. Photosynthesizing plants seem green because of the reflection of the yellow, green, and orange light off of their leaves.
How Do Different Spectra Affect Plant Growth?
Ultraviolet Light (10-400 nm)
UV light can be divided into three categories: UVA (320-400 nm), UVB (280-320 nm), and UVC (100-280 nm). However, only UVA and UVB are useful in the context of a grow room.
- UVA light (320-400 nm): UVA light is utilized in many grow lights but is not perceptible to humans. Studies have shown that 385 nm UV light facilitates the accumulation of phenolic compounds and promotes antioxidant activity in plant extracts without significantly affecting growth processes.
- UVB light (280-320 nm): It is not safe for human exposure but has been found to increase THC levels in Cannabis.
Depending on the intensity and duration of exposure, the effects of UV light on plants can vary. When plants are exposed to moderate doses of UV radiation, it can actually have positive effects. This exposure stimulates the production of secondary metabolites like flavonoids and anthocyanins. These compounds serve as antioxidants, providing protection to plants against UV damage. Furthermore, these metabolites can increase the nutritional and medicinal value of crops, offering additional benefits.
However, excessive levels of UV radiation can be harmful to plant tissues. It can cause mutations in DNA and inhibit photosynthesis, resulting in reduced growth, lower yields, and increased susceptibility to diseases and pests. In extreme circumstances, too much UV light can lead to cell death and even plant death.
Blue Light (400-500 nm)
Blue light, with its short wavelength and high energy, is an essential spectrum for plants. It serves several functions in plant physiology.
Firstly, blue light stimulates the production of chlorophyll, which is vital for photosynthesis. It plays a significant role in leaf development and promotes stem elongation. Additionally, blue light helps plants establish robust and healthy root systems. It also influences the opening and closing of stomata, which are tiny pores on the plant’s surface that regulate gas exchange.
Blue light achieves these effects by encouraging the production of auxins, which are plant hormones in charge of cell extension, division, and differentiation. Auxins accumulate on the shaded side of the plant, aiding the growth of roots and leaf tips toward water and nutrient sources. Moreover, auxins encourage cell elongation on the shaded side of the plant stem, leading the stem to lean toward the lighting. The presence of auxins also contributes to larger and thicker leaf growth due to increased cell division.
Green Light (500-570 nm)
Plants can utilize green light for photosynthesis, albeit less efficiently than red and blue light. While not as critical as other colors for plant growth, green light still contributes to various physiological processes. In terms of plant architecture, green light encourages shoot growth, resulting in taller and more slender plants, while thwarting root growth. This characteristic can be advantageous in situations where plants have limited space for root expansion, such as in hydroponic or aeroponic systems.
Furthermore, green light has the ability to penetrate deeper into the plant canopy compared with other wavelengths. This allows it to reach lower leaves that may be shaded, thereby increasing photosynthetic activity and leading to greater biomass accumulation.
Additionally, green light is instrumental in promoting the synthesis of secondary metabolites in plants, including flavonoids, phenolic acids, and carotenoids. Although these substances have no direct impact on plant growth, they play a vital role in plant survival and environmental stress response. Moreover, these secondary metabolites can be used in fields such as medicine and industry.
Yellow Light (570-590 nm)
Yellow light is less effective in driving photosynthesis compared with other wavelengths. Nevertheless, yellow light can interact with other light wavelengths to influence plant growth responses. When combined with blue light, it has been discovered to encourage root elongation in Arabidopsis thaliana seedlings. Similarly, a combination of red and yellow light has been shown to promote the accumulation of photosynthetic pigments in lettuce leaves.
Furthermore, yellow light may play a role in setting off environmental stress reactions such as dryness and salinity. For example, exposing tomato plants to yellow light has demonstrated a rise in their resistance to high salinity stress.
Although the precise mechanisms and effects of yellow light on plant growth and development are not yet fully understood, its potential significance in optimizing plant growth and production in diverse agricultural settings should not be overlooked.
Orange Light (590-620 nm)
Orange light, with a wavelength range of approximately 590-620 nm, may not be as crucial as red and blue light for plant growth and development. However, it still holds importance in promoting the health and productivity of plants and contributes to various physiological processes in plant growth.
Research studies have demonstrated the positive effects of orange light on the growth and development of specific plant species, such as tomatoes, lettuce, and strawberries. It helps the plant grow taller and have more leaves when combined with other spectra.
Red Light (640nm-680nm)
Red light plays a significant role in regulating various plant processes, especially in flowering and fruiting. It promotes blooming, fruit production and stem growth. 660nm has a powerful photosynthetic action among the red light wavelengths. It has a profound impact on the activation of red-absorbing phytochrome, which regulates important processes such as germination and flowering. This specific wavelength is highly effective for extending light cycles or interrupting the night period to induce flowering in long-day plants or prevent flowering in short-day plants.
Red light is also highly efficient in driving photosynthesis, contributing to the overall growth and development of plants. Its presence in a grow light spectrum helps balance the effects of far-red light and blue light. When the red light is dominant, it often stimulates the allocation of biomass to stems.
Far-red Light (> 700 nm)
Although the far-red light falls outside the PAR, it has a significant impact on the far-red absorbing form of phytochrome. It effectively converts the far-red form back to the red-absorbing form. This is particularly relevant for plants that require a relatively low phytochrome photoequilibrium to initiate the flowering cycle. By incorporating the far-red light at the end of each light cycle, flowering in short-day plants like Cannabis can be promoted.
Furthermore, maintaining a higher ratio of far-red to red light than what is typically found in sunlight can trigger a shade stretch response in plants. When plants sense an elevated ratio of far-red to red light, they tend to stretch and elongate their stems to outcompete neighboring plants for light. However, excessive levels of far-red light should be avoided if the goal is to maintain compact growth in plants, especially when using LED lights for cultivation.
Choose the Right Spectra at MokoLight
At MokoLight, we offer LED grow lights that provide a well-balanced spectrum of light, incorporating red, blue, white, and infrared wavelengths. While they are considered full-spectrum grow lights, they offer different ratios of red and blue light, allowing growers to select the most suitable spectrum for their specific plant needs.
In addition to full spectrum lighting, we also offer targeted spectrum lights with ultraviolet (UV) and infrared (IR) wavelengths. These specialized lights can be used to achieve specific plant growth objectives. Check out our LED grow lights and contact us for further information.