What is Light Spectrum: The Science Behind Full-Spectrum Light and Plant Growth
With the growing popularity of indoor cultivation, LED grow lights have become a vital tool for achieving healthy and abundant plants. These lights provide the ideal light spectrum, allowing gardeners to grow vibrant plants year-round. With a wide variety of LED grow lights on the market, the main difference lies in the science of the spectrum.
That's why we've created this comprehensive guide—to equip you with the knowledge needed to select the ideal full-spectrum grow lights for your garden. Let's explore the science behind full-spectrum lighting and plant development!
Table of Contents
The Science Behind Full-Spectrum Grow Light and Plant Growth
What Is the Light Spectrum
Effects of Different Visible Spectrums on Plant Growth
Red Light
Blue Light
Green Light
Yellow Light
Orange Light
Non-Visible Spectrums for Plant Growth: UV and IR
Ultraviolet Light
Infrared Light
Spectrum Science in LED Grow Lights
How to Read an LED Grow Light Spectrum Chart
Color Temperature (CCT)
Optimal Spectrum Lighting for Each Plant Stage
Seedling Stage
Vegetative Stage
Flowering and Fruiting Stage
Final Thoughts
What is the light spectrum?
The light spectrum encompasses the entire range of electromagnetic radiation wavelengths that we can perceive as light, including both visible and non-visible light. This spectrum ranges from gamma rays, which have the shortest wavelengths and highest energy, to radio waves, which have the longest wavelengths and lowest energy.
The light spectrum and visible spectrum in wavelengths (in meters)
The visible light spectrum is the portion of the electromagnetic spectrum that the human eye can detect, with wavelengths ranging from 380 to 750 nanometers (nm). Within this range, light is divided into different colors, each color corresponding to a specific wavelength, from violet at the shortest wavelengths to red at the longest.
Beyond the visible range lies the non-visible light spectrum. The ultraviolet (UV) region is just below 380 nm and includes shorter, more energetic wavelengths than visible light. At the other end of the spectrum, infrared (IR) light begins just above 750 nm and extends to much longer wavelengths. While also invisible to us, IR radiation is often felt as heat.
The entire light spectrum plays a role in various scientific, technological, and biological processes. In the context of plant biology, for example, specific portions of the light spectrum – particularly the blue and red regions of visible light – are essential for photosynthesis, while other parts, such as UV and IR, can indirectly influence growth, development, or stress responses.
Effects of Different Visible Spectrums on Plant Growth
The visible light spectrum consists of red, blue, green, yellow, and orange colors. Each color plays a unique role in plant development, including germination, vegetative growth, flowering, and fruiting.
Red Light
Red light on the spectrum
Red light, with wavelengths between 620 and 750 nm, plays a crucial role in plant growth. It is a key driver of photosynthesis and aids in various stages of plant development.
Plants absorb red light through a pigment called phytochrome, which switches between two forms: Pr (which absorbs red light) and Pfr (which absorbs far-red light). When exposed to red light, phytochrome switches to its active Pfr form, triggering the production of gibberellins—hormones that stimulate seed germination. This process occurs only in the presence of red light and water, ensuring that seeds germinate under favorable conditions.
Red light also increases the production of auxins, another class of hormones that promote cell elongation and expansion. These hormones are essential for processes like stem growth and root development.
In terms of reproduction, red light plays a significant role in flowering. In long-day plants, it acts as a signal to activate genes that initiate flowering. In short-day plants, it activates genes that delay flowering, allowing the plant to flower when conditions are ideal.
Furthermore, red light helps plants detect shade. When a plant is overshadowed by others, the ratio of red light to far-red light changes—chlorophyll absorbs red light, while far-red light is reflected. A higher proportion of far-red light signals to the plant that it is shaded, triggering a shade avoidance response that causes the stem to grow taller in search of more light.
Blue Light
Blue light on the spectrum
Blue light, with wavelengths between approximately 450 and 490 nm, is one of the most crucial parts of the light spectrum for plant growth. It has a short wavelength and high energy, making it particularly effective at driving several key developmental processes.
How does it do that? Blue light plays a central role in photosynthesis, exciting electrons in chlorophyll molecules, powering the light-dependent reactions that convert light energy into chemical energy. While it does not directly increase chlorophyll
Blue light affects plant development by influencing the distribution and activity of auxins. Auxins are primarily produced in the apical meristems, the growing tips of shoots and roots. In response to light, they tend to accumulate on the shaded side of the plant shoot, causing those cells to elongate more and bend the plant towards the light source. This is the basis of phototropism.
Furthermore, blue light signals stomata to open, activating specific receptors in the guard cells surrounding them, allowing for the intake of carbon dioxide and the release of oxygen, as well as the loss of water vapor through transpiration.
Green Light
Green light on the spectrum
Green light, with wavelengths ranging from approximately 495 to 570 nm, sits in the middle of the visible light spectrum. While not as crucial for plant growth as red and blue light, it still contributes to several important physiological processes.
Green light participates in regulating plant architecture, promoting shoot growth while inhibiting root growth. This effect can be beneficial in controlled environments, such as aeroponic or hydroponic systems, where space for root expansion is limited. Additionally, green light penetrates deeper into the plant canopy than other wavelengths, reaching lower leaves that would otherwise be shaded. This increases photosynthetic activity in those leaves, boosting overall biomass production.
Furthermore, green light stimulates the production of secondary metabolites, such as flavonoids, phenolic acids, and carotenoids. These compounds are not directly involved in growth but play essential roles in plant survival, helping them respond to environmental stresses.
Yellow Light
Yellow light on the spectrum
Yellow light, with wavelengths around 570-590 nm, is part of the visible spectrum that plants can absorb, but it is less effective at driving photosynthesis. While it may not significantly impact plant growth on its own, yellow light can interact with other wavelengths to influence growth responses.
For example, the combination of blue and yellow light can promote root elongation in Arabidopsis thaliana seedlings, while red and yellow light together can increase the production of photosynthetic pigments in lettuce. Yellow light can also help plants respond to environmental stresses, such as drought and salinity.
Orange Light
Orange light on the spectrum
Orange light, with wavelengths between 590 and 620 nm, may not be as crucial for plant growth as red or blue light, but it still plays an important role in promoting healthy and productive plants.
Orange light has been shown to positively affect the growth of certain plants, such as tomatoes, lettuce, and strawberries. For instance, supplementing red and blue light with orange light has been shown to increase plant height, leaf count, and fresh weight in lettuce seedlings, compared to using red and blue light alone.
Non-Visible Spectrums for Plant Growth: UV and IR
While ultraviolet (UV) and infrared (IR) radiation are outside the visible light spectrum, they play crucial roles in plant development.
UV light and infrared light on the light spectrum
Ultraviolet Light
Ultraviolet (UV) light is a high-energy form of radiation with wavelengths ranging from 10 to 400 nanometers. It is typically divided into three categories based on wavelength: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm).
UV radiation can affect plants in both beneficial and detrimental ways, depending on the intensity and duration of exposure. At moderate levels, UV light can trigger the production of secondary metabolites, such as flavonoids and anthocyanins. These compounds act as antioxidants, helping to protect plants from damage caused by UV radiation while enhancing the nutritional and medicinal qualities of crops.
On the other hand, excessive exposure to UV radiation can harm plant tissues, damaging DNA and interfering with photosynthesis. This can impair growth, reduce crop yields, and increase vulnerability to pests and diseases. In severe cases, it can even lead to cell damage and plant death.
Infrared Light
Infrared (IR) light is a low-energy radiation. The wavelength range of IR radiation spans from 700 nm to 1 millimeter (mm) and is divided into three categories: near-infrared (NIR, 700-1400nm), mid-infrared (MIR, 1400-3000 nm), and far-infrared (FIR, 3000 nm - 1 mm). In plant cultivation, NIR is the most commonly utilized.
IR light primarily acts through heat generation, warming plant tissues and indirectly stimulating metabolic activity and growth. This thermal effect can enhance various physiological processes, including the regulation of stomatal openings, which affects gas exchange and water loss.
Additionally, it also influences plant morphology, promoting stem elongation and leaf expansion in many species, while potentially accelerating flowering in others. Infrared light can also interact with plant hormonal systems, including auxins, gibberellins, and cytokinins, although these pathways are not as well understood
Both UV and IR light are "informational spectras" essential for plants. Currently, they are widely applied in agricultural and medical production. Check out our guide on how to use UV and IR for more practical use in your gardens.
Spectrum Science in LED Grow Lights
Science has shown that plants have specific light needs for optimal growth and development, which has led to the creation of LED grow lights with customized spectra. By understanding the science behind these lights, growers can optimize conditions for plant growth, resulting in healthier plants and more successful harvests.
How to Read an LED Grow Light Spectrum Chart
LED grow light spectrum charts are used to show the wavelength and intensity of light emitted by a particular grow light. These charts can be used to determine if the grow light is suitable for growing plants, as well as to compare the spectral outputs of different grow lights.
LED grow light spectrum chart
When reading an LED light spectrum chart, the x-axis represents the wavelength of light in nanometers (nm), and the y-axis represents the relative intensity of light in arbitrary units. The spectrum is typically displayed as a line graph, with different colors representing different wavelengths.
It's important to pay attention to the peaks and valleys in the spectrum, as different plant processes require specific light wavelengths. For example, chlorophyll absorption peaks around 450 nm (blue light) and 650-680 nm (red light), so a grow light with high intensity in these ranges is ideal for photosynthesis.
In addition to peak intensities, spectrum ratio is also an important consideration when choosing a grow light. The spectrum ratio is the ratio of red light intensity to blue light intensity and is typically displayed as a single number or as a graph. The ideal ratio varies depending on the plant species and your growing goals.
Full Spectrum LED
Full spectrum LED grow light spectrum chart
Full-spectrum LED grow lights are designed to provide a balanced and comprehensive light spectrum that closely mimics natural sunlight. The spectral characteristics of full-spectrum light typically include a mix of cool white and warm white LEDs, as well as specific wavelengths of blue, red, green, and sometimes UV and far-red light. While the exact spectral balance can vary between brands and models, most full-spectrum LED grow lights share a common characteristic: they have a higher proportion of blue and red light to emphasize their peaks.
Broad Spectrum LED
Broad spectrum LED grow light spectrum chart
Broad-spectrum LED grow lights are similar to full-spectrum LED grow lights in that they provide a range of wavelengths beneficial for plant growth and development. However, broad-spectrum LED grow lights tend to have a more even distribution of wavelengths across the visible spectrum, without emphasizing specific peaks in the blue or red regions. This can make them a good choice for growers looking for a balanced light source that promotes overall plant health and growth, without focusing too heavily on specific growth stages or plant characteristics.
Targeted Spectrum LED
Targeted Spectrum LED Grow Lights Spectrum Chart
Targeted Spectrum LED grow lights are designed to emit specific wavelengths that cater to different plant growth stages, such as vegetative growth or flowering. These lights primarily focus on blue and red light, with minimal green or yellow. Some models also include UV or far-red wavelengths, which can further influence plant development. By using these lights, growers can fine-tune the spectrum to meet their plants' specific needs, promoting healthy growth and maximizing yields.
Color Temperature (CCT)
Color temperature is a measure of the color appearance of light emitted by a light source and is measured in Kelvin (K). Lower color temperatures (2000-4000K) produce a warm, red-yellowish light, while higher color temperatures (5000-6500K) produce a cool, blue-white light. The color temperature of grow lights affects how plants perceive and react to light, influencing their growth and development.
The differences between color temperatures observed by human eyes
Ideal Spectrum Lighting for Each Plant Stage
Full-spectrum grow lights can meet a plant's basic lighting needs. However, as discussed earlier, plants respond particularly well to some specific light spectra at different growth stages. Therefore, to help plants reach their maximum potential, it is ideal to adjust the spectrum that offers the greatest benefits at each specific growth stage.
Let's use the tomato plant as an example to examine the ideal light conditions for each phase of its growth. For primary grow light, we recommend Mars Hydro TS1000 or FC1500—both professional LED lights that offer full spectrum, uniform PPFD, and smart controls—ideal for the entire growth cycle of tomatoes.
Seedling Stage
During the seedling stage, young tomato plants need gentle yet effective illumination to promote strong root development and robust stems, while avoiding stress. A full-spectrum LED light with a color temperature between 5000K and 6500K is ideal. This range offers a well-balanced blend of blue and red wavelengths, with an emphasis on blue light. The higher intensity of blue light encourages compact, healthy growth and helps prevent leggy, weak stems.
Tomato Plant in Seedling Stage
Lighting Setup:
Color Temperature: 5000K – 6500K
PPFD: 100–300 µmol/m²/s
Hanging Height: 25 cm (10 inches)
Photoperiod: 18 hours on / 6 hours off
Vegetative Stage
In the vegetative stage, a balanced spectrum is key, with a slight increase in blue light compared to red. A color temperature between 4000K and 5500K supports optimal foliage and stem development. Blue grow light encourages compact structure and strong stems, while red light promotes overall plant growth. For best results, consider adding targeted blue spectrum LEDs to fine-tune the light quality.
Tomato Plant in Vegetative Stage
Lighting Setup:
Color Temperature: 4000K – 5500K
PPFD: 400–600 µmol/m²/s
Hanging Height: 25 cm (10 inches)
Photoperiod: 18 hours on / 6 hours off
Supplemental Spectrum: Blue light synchronized with the main lighting cycle
Flowering and Fruiting Stage
In the flowering and fruiting stage, tomato plants benefit from a red-richer spectrum, with a color temperature between 3000K and 4000K. Red wavelengths trigger flowering hormones and stimulate reproductive growth. At this stage, too much blue light can cause plants to revert to vegetative behavior, so a reduced blue-to-red ratio is preferred. At this phase, utilizing additional UV+IR and Deep Red wavelengths can further enhance the results.
Tomato Plant in Fruiting Stage
Lighting Setup:
Color Temperature: 3000K-4000K
PPFD Required: 800–1000 µmol/m²/s
Hanging Height: 25 cm (10 inches)
Photoperiod: 12 hours on / 12 hours off
Supplemental Spectrum:
UV light for 10 minutes/h during the main light cycle
IR light for 15 minutes before main light on/after main light off
Deep Red light in sync with the main lighting operation cycle.
Final Considerations
When choosing LED Grow lights for cultivation, it is important to tailor the spectrum to the specific needs of your plants at each growth stage. Mars Hydro LED Grow lights offer a balanced spectrum with red, blue, white, and IR light, making them ideal for all growth stages, from seedling to harvest. With different red-to-blue ratios, growers can select the best option for optimal results. Mars Hydro also offers targeted spectrum lights, including UV and IR, for specific plant growth needs. Explore our collections of LED Grow Lights and contact us for more details.
Alpha Blunt Growshop provides Mars Hydro LEDs and other high-quality equipment for your indoor cultivation! Visit our Growshop and be amazed!