What is the Light Spectrum: The Science Behind Full-Spectrum Light and Plant Growth
With the increasing popularity of indoor cultivation, LED grow lights have become an indispensable tool for maintaining healthy and high-yielding plants. These lights provide the ideal light spectrum, enabling growers to cultivate lush plants all year round.
With the wide selection of LED grow lights on the market, the crucial difference lies in the precision of the light spectrum.
That's why we've created this comprehensive guide – to give you the knowledge you need to choose 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 Lights and Plant Growth
What is the Light Spectrum?
Effects of Different Visible Spectra on Plant Growth
Red Light
Blue Light
Green Light
Yellow Light
Orange Light
Non-Visible Spectra for Plant Growth: UV and IR
Ultraviolet Light
What is the Light Spectrum?
The light spectrum encompasses the entire range of wavelengths of electromagnetic radiation 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 the Visible Spectrum in Wavelengths (in meters)
The visible light spectrum is the part of the electromagnetic spectrum that the human eye can perceive, with wavelengths between 380 and 750 nanometers (nm). Within this range, light is divided into different colors, with each color corresponding to a specific wavelength, from violet at the shortest wavelengths to red at the longest.
Beyond the visible range is the non-visible light spectrum. The ultraviolet (UV) range lies just below 380 nm and includes wavelengths that are shorter and more energetic than visible light. At the other end of the spectrum, infrared (IR) light begins just above 750 nm and extends over much longer wavelengths. Although also invisible to us, IR radiation is often perceived as heat.
The entire light spectrum plays a role in various scientific, technological, and biological processes. In the context of plant biology, for example, certain parts 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 Spectra on Plant Growth
The visible light spectrum consists of the colors red, blue, green, yellow, and orange. Each color plays a unique role in plant development, including germination, vegetative growth, flowering, and fruiting.
Red Light
Red Light in the Spectrum
Red light, with wavelengths between 620 and 750 nm, plays a crucial role in plant growth. It is a key factor in photosynthesis and supports various developmental stages of plants.
Plants absorb red light through a pigment called phytochrome, which interconverts between two forms: Pr (which absorbs red light) and Pfr (which absorbs far-red light). When exposed to red light, phytochrome converts to its active Pfr form, triggering the production of gibberellins – hormones that stimulate seed germination. This process only occurs in the presence of red light and water, ensuring seeds germinate under favorable conditions.
Red light also increases the production of auxins, another class of hormones that promote cell growth and elongation. These hormones are essential for processes such as stem growth and root development.
Regarding 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 shaded by other plants, 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 in shade, triggering a shade-avoidance response that makes the stem grow taller to find more light.
Blue Light
Blue Light in the Spectrum
Blue light, with wavelengths between approximately 450 and 490 nm, is one of the most important components of the light spectrum for plant growth. It has a short wavelength and high energy, making it particularly effective in controlling various important developmental processes.
How does it work? Blue light plays a central role in photosynthesis by exciting electrons in chlorophyll molecules, thereby driving the light-dependent reactions that convert light energy into chemical energy. Although it does not directly increase chlorophyll content,
blue light influences plant development by affecting 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 these cells to elongate more and the plant to bend towards the light source. This is the basis of phototropism.
Additionally, blue light signals the opening of stomata by activating specific receptors in the surrounding guard cells. This allows for the uptake of carbon dioxide and the release of oxygen, as well as the loss of water vapor through transpiration.
Green Light
Green Light in the Spectrum
Green light, with wavelengths between approximately 495 and 570 nm, is in the middle of the visible light spectrum. Although not as critical for plant growth as red and blue light, it still contributes to several important physiological processes.
Green light is involved in regulating plant architecture by promoting shoot growth and 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 in shadow. This increases photosynthetic activity in these leaves and promotes 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 an essential role in plant survival by helping them respond to environmental stress.
Yellow Light
Yellow Light in the Spectrum
Yellow light, with wavelengths around 570–590 nm, belongs to the visible spectrum that plants can absorb, but it is less effective for photosynthesis. Although it does not significantly influence plant growth on its own, yellow light can interact with other wavelengths and thus influence growth responses.
For example, the combination of blue and yellow light can promote root growth 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 in the Spectrum
Orange light, with wavelengths between 590 and 620 nm, may not be as critical for plant growth as red or blue light, but it still plays an important role in promoting healthy and high-yielding plants.
Orange light has been shown to positively influence the growth of certain plants such as tomatoes, lettuce, and strawberries. For example, 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 Spectra for Plant Growth: UV and IR
Although ultraviolet (UV) and infrared (IR) radiation are outside the visible light spectrum, they play a crucial role in plant development.
UV Light and Infrared Light in the Light Spectrum
Ultraviolet Light
Ultraviolet light (UV) is a form of high-energy radiation with wavelengths between 10 and 400 nanometers. It is commonly 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 have both positive and negative effects on plants, depending on the intensity and duration of exposure. In moderate amounts, UV light can stimulate the production of secondary metabolites such as flavonoids and anthocyanins. These compounds act as antioxidants and help protect plants from UV radiation damage, while also increasing the nutritional value and medicinal properties of the plants.
On the other hand, excessive exposure to UV radiation can damage plant tissue, harm DNA, and impair photosynthesis. This can hinder growth, reduce crop yield, and increase susceptibility to pests and diseases. In severe cases, it can even lead to cell damage and plant death.
Infrared Light
Infrared light (IR) is low-energy radiation. The wavelength range of IR radiation extends 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 most commonly used.
IR light primarily works by generating heat, warming plant tissue and indirectly stimulating metabolism and growth. This thermal effect can enhance various physiological processes, including stomatal regulation, which affects gas exchange and water loss.
Furthermore, it also influences plant morphology by promoting stem elongation and leaf growth in many species, while potentially accelerating flowering in others. Infrared light can also interact with plant hormone systems, including auxins, gibberellins, and cytokinins, although these pathways are not yet as well understood.
Both UV and IR light are essential "information spectra" for plants. Today, they are widely used in agricultural and medical production. Read our guide on the practical use of UV and IR light in your gardens.
Spectral Science in LED Grow Lights
Science has shown that plants have specific light needs for optimal growth and development, leading to the development of LED grow lights with tailored spectra. By understanding the science behind these lights, growers can optimize plant growth conditions, leading to healthier plants and more successful harvests.
LED Light Spectrum Chart for Plant Cultivation
When viewing an LED light spectrum chart, the x-axis represents the wavelength of light in nanometers (nm), while the y-axis indicates the relative light intensity in arbitrary units. The spectrum is usually displayed as a line graph, with different colors symbolizing different wavelengths.
It is important to pay attention to the peaks and troughs in the spectrum, as different plant processes require specific light wavelengths. For example, chlorophyll absorption peaks at approximately 450 nm (blue light) and 650–680 nm (red light), so a grow light with high intensity in these areas is ideal for photosynthesis.
In addition to peak intensities, the spectrum ratio is also an important factor when choosing a grow light. The spectrum ratio is the ratio between the intensity of red and blue light and is usually represented as a single number or a graph. The ideal ratio varies depending on the plant species and your cultivation goals.
Full-Spectrum LED (Full Spectrum)
Spectrum Chart for Full-Spectrum LED Grow Lights
Full-spectrum LED grow lights are designed to provide a balanced and complete light spectrum that closely mimics natural sunlight. The spectral properties of full-spectrum light typically include a mix of cool and warm white LEDs, as well as specific wavelengths of blue, red, and green light, and sometimes also UV and far-red light. Although the exact spectral composition may vary depending on the brand and model, most full-spectrum LED grow lights have a common characteristic: they have a higher proportion of blue and red light to emphasize their peak values.
Broadband LED
Spectrum Chart for Broadband LED Grow Lights
Broadband LED grow lights are similar to full-spectrum LED grow lights in that they cover a range of wavelengths beneficial for plant growth and development. However, broadband LED grow lights tend to have a more even wavelength distribution across the entire 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 general plant health and growth without focusing too heavily on specific growth stages or plant characteristics.
Targeted Spectrum LEDs
Spectrum Chart of "Grow" LED Grow Lights with Targeted Spectrum
Espectro Direcionado LED grow lights are designed to emit specific wavelengths tailored to different plant growth stages, such as vegetative growth or flowering. These lights primarily focus on blue and red light, with a minimal amount of green or yellow light. Some models also feature UV or far-red wavelengths, which can further influence plant development. By using these lights, growers can customize the spectrum to the specific needs of their plants, promoting healthy growth and maximizing yield.
Color Temperature (CCT)
Color temperature is a measure of the color appearance of light emitted by a light source, measured in Kelvin (K). Lower color temperatures (2000–4000 K) produce a warm, yellowish-red light, while higher color temperatures (5000–6500 K) produce a cool, bluish-white light. The color temperature of grow lights affects how plants perceive and respond to light, which in turn impacts their growth and development.
The differences in color temperatures perceived by the human eye
Ideal light spectrum for each plant growth stage
Full-spectrum grow lights can meet a plant's basic lighting needs. However, as mentioned earlier, plants respond particularly well to specific light spectra during different growth phases. To help plants reach their full potential, it is therefore ideal to adjust the spectrum to provide the greatest benefits in each specific growth stage.
Let's take the tomato plant as an example to examine the ideal lighting conditions for each phase of its growth. For primary cultivation lighting, we recommend the Mars Hydro TS1000 or FC1500 – both professional LED lights that offer a 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 but effective lighting to promote vigorous root development and robust stems, while avoiding stress. A full-spectrum LED light with a color temperature between 5000 K and 6500 K is ideal. This range provides a balanced mix of blue and red wavelengths, with an emphasis on blue light. The higher intensity of blue light promotes compact and healthy growth and prevents long, weak stems.
Tomato plant in the seedling stage
Lighting configuration:
Color temperature: 5000 K – 6500 K
PPFD: 100–300 µmol/m²/s
Hanging height: 25 cm
Photoperiod: 18 hours on / 6 hours off
Vegetative Stage
In the vegetative stage, a balanced light spectrum is crucial, with a slightly increased blue component compared to red. A color temperature between 4000 K and 5500 K promotes optimal leaf and stem development. Blue plant light promotes a compact structure and strong stems, while red light supports overall plant growth. For best results, consider using targeted blue LED lights to adjust the light quality.
Tomato plant in the vegetative stage
Lighting configuration:
Color temperature: 4000 K – 5500 K
PPFD: 400–600 µmol/m²/s
Hanging height: 25 cm
Photoperiod: 18 hours on / 6 hours off
Additional spectrum: Blue light, synchronized with the main lighting cycle
Flowering and Fruiting Stage
In the flowering and fruiting stage, tomato plants benefit from a spectrum rich in red light, with a color temperature between 3000 K and 4000 K. Red wavelengths activate flowering hormones and stimulate reproductive growth. At this stage, an excess of blue light can cause plants to revert to vegetative growth; therefore, a reduced blue-to-red ratio is preferable. In this phase, the use of additional UV+IR and deep-red wavelengths can further improve results.
Tomato plant in the fruiting stage
Lighting configuration:
Color temperature: 3000 K–4000 K
Required PPFD: 800–1000">800–1000 µmol/m²/s
Hanging height: 25 cm (10 inches)
Photoperiod: 12 hours on / 12 hours off
Additional spectrum:
UV light for 10 minutes/hour during the main light cycle
IR light for 15 minutes before turning on the main light / after turning off the main light
Deep red light synchronized with the main lighting's operating cycle.
Final Considerations
When selecting LED grow lights for cultivation, it is important to match the spectrum to the specific needs of your plants in 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. Thanks to different red-to-blue ratios, growers can choose the best option to achieve optimal results. Mars Hydro also offers lights with targeted spectrums, including UV and IR, for specific plant growth needs. Discover our collections of LED grow lights and contact us for more details.
Alpha Blunt Growshop supplies LED lights from Mars Hydro and other high-quality equipment for your indoor cultivation! Visit our grow shop and be amazed!