If your indoor plants seem to struggle despite having the proper water habits and soil quality, chances are, there’s a problem with the light quality they receive.
Not all grow lights are created equal, and the spectrum they provide makes a big difference in your plant’s development. The light spectrum is important in plant development as it triggers photosynthesis.
But don’t just shine any grow light on your plant. Grow lights have specific spectrums that trigger Photosynthesis. And to get the ideal result, you need to understand what spectrum works best for each stage of plant growth.
Table of Contents
- Understanding Light Spectrum and Plant Growth
- What is Photosynthetically Active Radiation (PAR)?
- Spectrums for Plant Growth
- Blue Light (400-500 nm)
- Red Light (600-700 nm)
- Green Light (500-600 nm)
- UV Light (Below 400 nm)
- Infrared (IR) Light (Above 700 nm):
- Full Spectrum vs. Targeted Spectrum Grow Lights
- Matching the Spectrum to Growth Stages
- Seedling Stage: Focus on Blue Light
- Vegetative Stage: Add more Blue
- Flowering or Fruiting Stage: Increase Red and Infrared Light
- What Happens When the Wrong Spectrum is Used?
- Can Side Effects of Using the Wrong Spectrum Be Fixed?
- Conclusion
- Frequently Asked Questions About Grow Light Spectrums
Understanding Light Spectrum and Plant Growth
The light spectrum refers to the range of wavelengths, or colors, emitted by a light source. Plants absorb these wavelengths, using them to trigger essential processes like photosynthesis.
Sunlight naturally provides the full light spectrum. For indoor plants to get the same benefits, they rely on grow lights to achieve the same spectrums. Grow lights have a certain balance of spectrums needed for stages of plant growth, which allow indoor growers to have lush and thriving indoor gardens.
What is Photosynthetically Active Radiation (PAR)?
Photosynthetically Active Radiation, or PAR refers to the range of light usable for plants and is measured in nanometers (nm).
Lights with higher PAR outputs provide more usable energy, translating to
robust and healthier plants. When choosing grow lights, pay attention to the PAR levels so that your plants become strong until it’s time to harvest.
Spectrums for Plant Growth
Another thing you will notice when selecting grow lights are colors, which are the spectrums these fixtures cover. Each color or spectrum has a particular benefit in a plant’s development.
Blue Light (400-500 nm)
Essential for the early stages of plant growth, blue light is used to strengthen root development and encourage thick, leafy growth.
Best for developing seedlings, vegetative growth, and leafy greens like lettuce or spinach.
Red Light (600-700 nm)
Promotes flowering, fruiting, and stem elongation. It signals plants to focus energy on blooming and producing fruits.
Best for the later stages of growth, flowering plants, and fruit-bearing crops.
Green Light (500-600 nm)
Although plants don’t absorb green light as effectively as red or blue, it helps penetrate the canopy to ensure shaded parts of the plant can continue photosynthesizing.
Best for general plant health and ensuring even light distribution in dense gardens.
UV Light (Below 400 nm)
Often used as supplementary lighting, UV improves a plant’s resistance to pests and disease. It also enhances the oils, flavors, and scents of fruit-bearing plants and flowers.
Best for specialty crops, herbs, and flowering plants.
Infrared (IR) Light (Above 700 nm):
Infrared light stimulates cell elongation and flowering, speeding up the blooming process. It’s best used in the final stages of plant growth.
Best for flowering plants, fruiting-bearing plants, and increasing yields during bloom phases.
Full Spectrum vs. Targeted Spectrum Grow Lights
Another thing you will notice when choosing grow lights is their classifications. Often you will encounter full spectrum and stage-specific spectrum grow lights.
Full Spectrum Grow Lights
If there was a way to bring the sun indoors, then full spectrum grow lights are the way to go. These grow lights deliver the wavelengths found in natural sunlight to your indoor garden.
Since these provide a balanced blend of colors, full-spectrum grow lights have the widest range needed for plants.
If you’re looking to grow a variety of plants in the future indoors, these grow lights are a good consideration. They can handle leafy vegetables and even fruit-bearing plants like tomatoes. Likewise, it’s a good way to simplify indoor gardens since you don’t have to factor in swapping out lights between stages.
Targeted Spectrum Lights
Some plants require particular spectrums during stages. Plants like lettuce, spinach, and herbs, are best grown under a targeted spectrum. If this is your garden’s focus, using a vegetative stage grow light is best.
While using a full spectrum will also work, it will cost more than a grow light for vegetation.
In some cases, targeted spectrum lights are used to supplement an existing grow light. For instance, UV lights are added to improve plant resilience and overall quality.
Matching the Spectrum to Growth Stages
The light spectrum you use significantly impacts how your plants develop from day one to harvest day. Let’s break down how to match your grow light spectrum to the key phases of plant growth to encourage stronger plants, better yields, and healthier harvests.
Seedling Stage: Focus on Blue Light
Blue light (400-500 nm) is essential for promoting compact growth and healthy leaf formation in the seedling stage.
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Use grow lights heavy in blue wavelengths with some red for balance.
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Keep the light close to the seedlings, but do not crank it up. Gentle blue light encourages them to grow bushy and strong without stretching.
Vegetative Stage: Add more Blue
A good amount of blue light helps prevent legginess or tall, weak growth and promotes a lush canopy. Adding a touch of red can also stimulate energy production.
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If you’re using full spectrum lights, start with a ratio of 60:40.
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Depending on the plant, you can keep the lights on for 14 -18 hours daily.
Flowering or Fruiting Stage: Increase Red and Infrared Light
If you’re growing plants that bear fruits or flowers, increase red and infrared lighting to signal plants to produce flowers and fruits.
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You can add a touch of blue light to support overall plant health for full-spectrum lighting.
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Lighting duration will also depend on the plants, but it can last between 12 -14 hours.
What Happens When the Wrong Spectrum is Used?
Using the wrong spectrum or mismatched lighting can lead to more harm. That is why it is critical to know when to exactly use each spectrum. To give you an idea of what to expect when lighting is mismatched:
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Too much red light in the early stages can cause plants to become leggy and weaken the stems, leading to thinner foliage.
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Too much blue light during the flowering stage can affect fruit development, causing more energy to be diverted into foliage development.
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Not using UV for certain crops can reduce flavor and aromas of the end product.
Can Side Effects of Using the Wrong Spectrum Be Fixed?
The good news is that spectrum mismatches can be corrected before long-term damage occurs. You can adjust full spectrum lights or add targeted supplemental lighting to fix this problem.
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If there’s a growth slowdown, add an hour of additional exposure.
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You should notice stronger growth and improved vigor within a week or two with the right adjustments.
Conclusion
Light is the foundation of plant health and productivity. By understanding and matching the right light spectrum to each stage of plant growth, you can improve yields, and ensure your plants thrive from seedling to harvest.
Remember that the key is to provide plants with the wavelengths they need at the right time. With the right spectums, your indoor garden can flourish, producing lush greenery, vibrant flowers, and abundant fruits.
If you’re ready to start indoor growing, check our selection of grow lights, including those that target particular spectrums. Be sure to check the most popular grow lights in the market to give you an idea of the best options in the market.
Frequently Asked Questions About Grow Light Spectrums
- ◄What is the best light spectrum for plant growth?
- Different growth stages require different spectrums. Blue light (400-500 nm) is ideal for seedlings and vegetative growth, while red light (600-700 nm) promotes flowering and fruiting.
- ◄Why is light spectrum important for indoor plants?
- Light spectrum directly affects photosynthesis and plant development. The right balance ensures strong roots, healthy leaves, and better yields.
- ◄What is Photosynthetically Active Radiation (PAR)?
- PAR is the range of light (400-700 nm) that plants can use for photosynthesis. Higher PAR levels result in stronger, healthier plants.
- ◄Should I use full spectrum or targeted spectrum grow lights?
- Full spectrum lights mimic natural sunlight and are great for all growth stages. Targeted spectrum lights are best for specific plant needs, such as blue for vegetative growth and red for flowering.
- ◄Can using the wrong spectrum harm my plants?
- Yes. Too much red light early on can cause weak stems, and too much blue light during flowering can reduce fruit production. Matching the spectrum to the growth stage is key.
- ◄How many hours should grow lights be on?
- It depends on the plant's stage: seedlings need 14-16 hours, vegetative plants 14-18 hours, and flowering plants 12-14 hours.
- ◄Do plants need UV or infrared (IR) light?
- UV light enhances plant resistance to pests and boosts flavors in herbs and fruits. IR light promotes flowering and cell elongation in the late growth stages.
- ◄How do I fix issues caused by the wrong light spectrum?
- Adjust your lighting setup by switching to the correct spectrum or adding supplemental lighting. Plants typically recover within 1-2 weeks.
- ◄What happens if my plants don't get enough light?
- Plants may become leggy, weak, and produce fewer flowers or fruits. Ensure they receive adequate light based on their growth stage.
- ◄Are grow lights necessary for all indoor plants?
- While some houseplants can survive in low light, grow lights are essential for optimal growth, especially for fruiting or flowering plants indoors.
