Spectral Manipulation in Greenhouse Lighting
April 9, 2025 In the past dozen years of working with greenhouse and indoor growers, researchers, and engineers in the burgeoning grow lighting world, I’ve witnessed the evolving understanding (and sometimes misunderstanding) of how different light spectra can affect plant growth. While manipulating the light spectrum offers exciting possibilities for optimizing growth, determining the most strategic approach requires balancing multiple factors.
Different parts of the light spectrum have different effects on plants, including biomass and growth rate. | Photo: Magdalene Mastin
Understanding Spectrum Impacts
The fundamental tradeoff when changing light spectrum is quantity versus quality—compactness versus expansion, secondary metabolite production versus raw biomass. Different parts of the spectrum create distinct trends:
- Blue spectrum: Produces less total biomass, but creates more compact, thick plants with higher secondary metabolite concentrations (compounds like antioxidant anthocyanins and others that enhance nutritional value, taste, and coloration) and greater stress and pest resistance.
- Far-red spectrum: Encourages expansion/extension, helps plants fill growing space faster, and increases overall growth rate by triggering shade-avoidance responses.
- Full, balanced spectrum: Most closely mimics natural sunlight, providing the benefits of both blue and red wavelengths. This approach works best for most applications where extreme plant manipulation isn’t necessary, supporting natural development across growth stages.
More often than not, the blue side of the spectrum will produce more compact, thicker plants that have better transplant quality and shipping durability. This is especially important if you’re growing plants that will be moved or transplanted before reaching their final growing location.
Real-world Applications
At MBG Marketing in Michigan, North America’s largest grower-owned marketer of blueberries, we recently installed 64,000 watts of energy-efficient LEDs with far-red and blue spectrum tuning capabilities. Because MBG grows hundreds of different crosses for customers across the country, a tunable full-spectrum toolbox provides tremendous flexibility.
In practice, they use increased far-red during the early vegetative stage to encourage faster leaf expansion, then shift to higher blue light intensity when preparing plants for shipping to growers. During winter months with low natural light, they adjust to a more balanced spectrum to maximize growth while maintaining plant quality. The result? Southern highbush blueberries blooming inside a snow-covered Michigan greenhouse in December, with stronger, healthier plants ready for their grower customers.
At York College in Pennsylvania, we created an educational setup with four distinct light spectrums ranging from pure blue to pure far-red over greenhouse NFT lettuce plants. This experimental approach demonstrates what each spectrum can do at a small scale. Students can observe how different light recipes affect leaf expansion, coloration, and nutrient content in real time, ultimately providing a toolbox of strategies to utilize at a larger scale in their future careers.
Greenhouse operators should consider their budget, technical capacity, and other factors before implementing spectral manipulation in their facility. | Photo: Magdalene Mastin
When Spectral Manipulation Makes Sense
Not every operation will benefit from advanced spectral manipulation. Several factors increase the likelihood it’s worth implementing:
- Light source dominance: What percentage of light comes from LEDs versus natural light? The more artificial light dominates, the greater impact spectral changes will have.
- Value of secondary attributes: If coloration, quality, or chemical concentrations significantly impact your bottom line, spectral manipulation becomes more valuable.
- Crop consistency: The more consistent your crops and genetics are, the more finely you can tune your lighting for predictable, optimal results.
- Technical capacity: Consider your team’s ability to manage additional variables in your growing system.
- Budget and incentives: Utility incentives can make advanced lighting more accessible.
Leafy greens, herbs, and microgreens are examples with greater potential for spectral benefits, particularly when red coloration is desirable for visual appeal and nutritional value.
Common Misconceptions
Beware of oversimplifications about light spectrum. A persistent misconception based on historic lighting technology is that you need blue light for vegetative growth and red light for flowering. While there’s some truth here, it’s usually overstated. Both spectrums provide benefits at all growth stages.
Another mistake is treating spectrum as binary rather than considering intensity. Including far-red or UVA in your lighting doesn’t guarantee results—the amount matters tremendously. Too little might have little to no effect, while too much could be detrimental.
Implementing Wisely
If you’re considering spectral manipulation for the first time, I recommend a measured approach:
- Identify a manageable first step, perhaps testing different spectrums in a small section of your grow space.
- Consider whether a fixed spectrum optimized for your specific crops might be more cost-effective than full tunability.
- Work with lighting partners experienced in your crops and growing situation who can share relevant case studies.
As technology advances and costs decrease, spectral manipulation will become more accessible. The key is determining whether the benefits for your specific situation justify the additional complexity and investment. Sometimes the simplest approach—adding more light of the right quality—remains the wisest path forward.