The global demands for sustainable and healthy crop production, without reliance on chemical fertilizers and pesticides, have increased significantly in recent decades1,2. Controlled-environment vertical farms (CEVFs), which use hydroponic systems and light-emitting diodes (LEDs) as artificial light sources, have emerged as promising systems to meet these demands3. CEVFs allow high-density cultivation of a wide range of crops in compact urban spaces, independent of external environmental factors4. In addition to enabling all-season farming, LED-based lighting systems provide spectral control over plant growth. However, despite their advantages, CEVFs are often criticized for their high energy consumption, much of which is related to artificial lighting. The type and spectral composition of LED light significantly affect both the energy efficiency and productivity of CEVFs. Different LED wavelengths vary in their energy-to-photon conversion efficiency and optimizing light spectra can reduce electricity cost while maximizing biomass output5. LEDs also influence plant development both directly (e.g., altering morphology and physiology) and indirectly (e.g., enhancing photosynthesis)6,7,8. Therefore, adjusting the spectral quality and intensity of LED lighting is essential for both economic and biological optimization of vertical farming systems.

Although the advantages of LEDs in CEVFs are well documented, optimizing their efficiency for specific crops still required detailed investigation into how different spectral compositions and light intensities affect plant growth and development. Numerous studies have explored the influence of LED spectra on various crops9,10,11, with particular attention to the width or narrowness of the wavelength range, and whether single-color or multispectral combinations are more effective11,12.

The photosynthetically active radiation (PAR) spectrum, defined as 400–700 nm, includes blue (B, ~ 400–450 nm), green (G, ~ 500–600 nm), and red (R, ~ 600–700 nm) wavelengths, each playing distinct roles in plant development13. Red and blue light are particularly critical for photosynthesis and photomorphogenesis. Numerous studies have demonstrated that red:blue (R:B) ratio can significantly influence plant growth, although the optimal ratio is species-dependent14,15,16. For lettuce and basil an R:B ratio around 3:1 has been suggested to promote improved growth performance17.

Beyond blue and red, other spectral regions such as green and yellow light have been explored for their physiological effects18,19. Green light has the ability to penetrate deeper into the plant canopy than red or blue, potentially enhancing light distribution and supporting photosynthesis in lower leaves20,21. However, the role of green light remains debated. While some studies highlight its contributions to plant growth, others suggest it is less efficient and unnecessary in artificial lighting setups18,22. Similarly, the impact of yellow light (Y, ~ 550 nm) on plant growth is not well understood, with some evidence indicating a negative effect on development23. These mixed findings underscore the complexity of spectral responses and the importance of evaluating combinations of wavelengths rather than isolated colors.

Far red (FR, 700–800 nm) light, although outside the traditional PAR range, has received growing attention for its ability to enhance plant growth by promoting shade avoidance response, increasing canopy expansion, and improving light absorption24. However, the optimal ratio of red to far-red (DR:FR) and its effect on plant physiology, including chlorophyll concentration, remains subjects of ongoing debate25,26. Recent studies have shown that FR supplementation can significantly enhance biomass production and canopy size in crops like lettuce and tomato, although in some cases this comes at the cost of reduced pigment or mineral content27,28. Yield improvements of up to 25% in tomato and 39% in lettuce have been reported when FR light was applied at specific durations during the photoperiod29,30. These findings highlight that both the intensity and timing of FR application are critical to achieving benefits without compromising crop quality.

In addition,31 broad-spectrum lighting, which more closely resembles natural sunlight, may outperform narrow-spectrum lighting in supporting plant growth and development31. Lu et al.31 demonstrated that broad-spectrum LEDs improved plant growth compared to single- or dual-band lighting. Studies have also shown that combining red and blue light with white LEDs can enhance plant morphology and visual quality, particularly in leafy crops such as lettuce32. Meng and Runkle24 reported that combining white, red, blue and far-red light lead to greater lettuce yield than narrower spectra.

Another key consideration in designing lighting strategies for vertical farms is photon flux density (PPFD), which determines the total light intensity received by the plants. Although optimal values vary across crops and setups, studies suggest that a PPFD of 250 μmol m−2 s−1, combined with an R:FR ratio 11:5, supports robust lettuce growth33, while spinach may perform better under lower intensities, such as 100 μmol m−2 s−1 with an R:B of 4:134. However, these findings are based on individual experiments and may not apply universally. Additionally, most do not consider the potential benefits of dynamic lighting, which adjusts light quality and intensity in response to crop development or energy costs, as discussed in recent literature35.

In this study, we tested the impact of adding supplemental deep red (660 nm) and far red (730 nm) LEDs to a fixed white LED background. The treatments created different spectral compositions, not isolated wavelengths, and were designed to reflect realistic conditions used in commercial CEVFs. We also evaluated the effect of increasing PPFD by doubling the total photon output in one treatment. The test crops, lettuce (Lactuca sativa cv. Batavia-Caipira) and basil (Ocimum basilicum cv. Emily), were selected because they represent widely cultivated leafy greens and herbs in vertical farms, with different light sensitivity profiles and growth habits (cool-season vs. warm-season).

We hypothesized that the addition of DR and FR light to a white LED base, and adjusting their relative intensities, would enhance growth parameters such as biomass accumulation, canopy development, and nutrient content. We further expected that increasing total PPFD would improve growth responses, but only when spectral quality was optimized.