LED Spectral Composition and Daily Light Integral for Energy-Efficient Basil Production in Plant Factory Systems: A Systematic Review

1. Introduction

Global agriculture faces increasing pressure from population growth, climate variability, urbanization, and resource limitations [1,2]. Controlled-environment agriculture (CEA) has emerged as an alternative approach because it allows temperature, humidity, light, and other production factors to be regulated more precisely than in open-field systems [3,4]. Plant factories with artificial lighting (PFALs) represent a highly controlled form of CEA and enable year-round production in space-limited environments [3,5].

PFALs can improve production consistency and reduce dependence on external climatic conditions [1,3]. However, artificial lighting remains a major component of energy demand in indoor production systems [6,7]. Consequently, lighting optimization is important for improving both crop performance and the economic and environmental sustainability of PFAL production [8,9]. Figure 1 illustrates the main components of a plant factory system with artificial lighting (PFAL), including multilayer cultivation, LED illumination, and environmental control systems.

Light-emitting diodes (LEDs) have increased the precision with which light can be managed in CEA systems [10,11]. LED systems allow growers to modify spectral composition, photosynthetic photon flux density (PPFD), and photoperiod according to crop requirements [5,11]. Light also acts as a developmental signal and regulates photosynthesis, plant architecture, stomatal behaviour, and secondary metabolism [10]. These responses make spectral quality and light quantity important components of crop-specific lighting strategies [11,12].

Basil (Ocimum basilicum L.) is well suited to controlled-environment production because of its short production cycle, high commercial value, and adaptability to hydroponic systems [11,13]. Its value also depends on quality traits such as phenolic compounds, antioxidant activity, essential oils, and volatile compounds [13,14]. LED treatments can modify these traits together with biomass and plant morphology [12,14]. Recent studies further show that basil responses can differ with spectral composition, cultivar, light intensity, and photoperiod [15,16,17].

Despite substantial research, the reported responses of basil to LED lighting remain heterogeneous [10,11]. Studies conducted at the same daily light integral (DLI) can produce different responses when PPFD and photoperiod are changed [15,18]. Spectral treatments can also produce different effects on biomass, morphology, volatile compounds, and sensory quality [16,17,19]. Recent work in vertical-farm and greenhouse systems further demonstrates that lighting responses depend on the production environment and the balance between productivity and energy use [9,19]. These findings indicate that a single lighting recipe cannot be assumed to be optimal for all basil production systems [10,11].

Previous reviews have examined the effects of light intensity, duration, and spectral distribution on basil production [5,11]. However, the evidence base has expanded with recent studies on DLI, photoperiod, far-red light, supplemental lighting, volatile compounds, and energy-use performance [9,15,16,17]. These factors are also frequently evaluated separately rather than within an integrated production framework [10]. A systematic synthesis is therefore needed to distinguish consistent responses from context-dependent effects and to identify lighting strategies that balance productivity, product quality, and energy demand. Accordingly, this review evaluates the effects of LED spectral composition and light quantity on basil growth, morphology, physiological responses, phytochemical and essential-oil characteristics, and energy-use efficiency under controlled-environment conditions.

2. Materials and Methods

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines to identify and synthesize relevant evidence on the effects of LED spectral composition, photosynthetic photon flux density (PPFD), photoperiod, and daily light integral (DLI) on basil (Ocimum basilicum L.) production under controlled-environment conditions [20]. Studies were identified through searches of Web of Science, Scopus, ScienceDirect, and Google Scholar using combinations of the keywords “Ocimum basilicum”, “basil”, “LED”, “light-emitting diode”, “artificial lighting”, “plant factory”, “controlled environment”, “vertical farming”, “light spectrum”, “spectral composition”, “red light”, “blue light”, “green light”, “far-red”, “UV-A”, “UV-B”, “photosynthetic photon flux density”, “PPFD”, “daily light integral”, “DLI”, and “photoperiod”. Additional terms describing plant responses included “biomass”, “growth”, “morphology”, “photosynthesis”, “phenolic compounds”, “flavonoids”, “antioxidant activity”, “essential oil”, “volatile compounds”, and “energy-use efficiency”. The literature search was conducted between January 2025 and July 2026.

Inclusion criteria comprised peer-reviewed articles published in English that examined O. basilicum grown under artificial or supplemental LED lighting and evaluated at least one of the following factors: spectral composition, PPFD, photoperiod, or DLI. Eligible studies were required to report quantitative responses related to biomass, morphology, physiology, phytochemical composition, essential oils, volatile compounds, or energy use. Studies conducted in controlled-environment chambers, greenhouses with supplemental lighting, and plant factory systems with artificial lighting (PFALs) were considered eligible. Exclusion criteria comprised non-peer-reviewed publications, conference abstracts without complete datasets, studies focused on crops other than O. basilicum, studies conducted solely under open-field conditions without controlled lighting, and studies that did not report relevant quantitative outcomes. Retrieved records were exported and managed using reference-management software, and duplicate records were removed before screening. The study-selection process followed the PRISMA framework from identification and screening through eligibility assessment and inclusion [20].

3. Results and Discussion

A total of 800 records were identified through the database search, of which 180 duplicate records were removed. Following title and abstract screening, 420 records were excluded, leaving 200 reports for retrieval. All 200 reports were retrieved and assessed for eligibility. Of these, 140 reports were excluded, and 60 studies met the inclusion criteria and were included in the final qualitative synthesis (Figure 2). The included studies examined the effects of LED spectral composition, photosynthetic photon flux density (PPFD), photoperiod, and daily light integral (DLI) on basil growth, morphology, physiological responses, phytochemical composition, essential oils, volatile compounds, and energy-use performance. The evidence was synthesized comparatively according to lighting treatment, production system, cultivar, and production objective to distinguish consistent responses from context-dependent effects.

3.1. Plant Factory Systems with Artificial Lighting (PFALs) as a Platform for Basil Production

The reviewed studies show that plant factory systems with artificial lighting (PFALs) and other controlled-environment systems provide suitable platforms for evaluating basil responses to controlled lighting conditions [21,22]. These systems allow light intensity, spectral composition, and photoperiod to be regulated while other environmental factors are maintained under controlled conditions [7,21]. Recent studies have demonstrated that changes in lighting conditions can affect basil biomass, morphology, flowering, phytochemical composition, and volatile compounds [7,21]. The magnitude and direction of these responses, however, vary with cultivar, light intensity, spectral composition, and developmental stage [7,15]. These findings indicate that controlled-environment production provides a useful basis for comparing lighting treatments, but basil responses should be interpreted in relation to the specific combination of lighting and production conditions examined [15,22].

Basil (Ocimum basilicum L.) is well suited to controlled-environment production because of its short growth cycle and adaptability to hydroponic systems, while its growth is strongly influenced by light intensity and spectral conditions [7,22]. Increasing PPFD increased fresh mass, dry matter content, and plant height in three basil cultivars grown in a vertical farm [22]. However, the magnitude and form of these responses differed among cultivars [22]. Similarly, increasing broadband LED intensity affected biomass, morphology, marketability, and light-use efficiency in four basil cultivars [7]. These findings show that basil responses to artificial lighting depend on both cultivar and light intensity [7,22].

Basil production involves both biomass and quality attributes, including phenolic compounds, antioxidant activity, essential oils, volatile compounds, and sensory characteristics [7,14]. Lighting treatments can modify these quality attributes together with plant growth and morphology under controlled conditions [7,16]. Continuous lighting at a constant DLI also increased antioxidant capacity, chlorophylls, flavonoids, and phenols in sweet basil without significantly affecting plant growth [18]. Supplemental LED lighting can further alter volatile compounds and sensory attributes in indoor-grown basil, showing that lighting effects extend beyond biomass production [16]. These responses increase the importance of evaluating lighting strategies according to both production and quality objectives [7,16,18].

LED technology allows precise control of spectral composition, photosynthetic photon flux density (PPFD), and photoperiod in controlled-environment basil production [7,22,23]. Spectral treatments can modify biomass, plant morphology, photosynthetic responses, phytochemical accumulation, essential-oil composition, and volatile compounds [14,22,23]. However, these responses vary with the spectral combination and experimental conditions [22,24]. Supplemental blue, green, and red LEDs produced different changes in polyphenols, anthocyanins, and volatile profiles without significantly affecting biomass in two sweet basil cultivars [25]. Supplemental blue and red light also altered key aroma volatiles in hydroponically grown ‘Italian Large Leaf’ basil [26]. Different LED spectra further modified essential-oil composition and plant morphology in O. basilicum [27]. These findings indicate that LED lighting can be used to regulate biomass, morphology, and product quality according to specific production objectives [22,25,26,27].

Artificial lighting is a major energy input in plant factory systems with artificial lighting (PFALs), making lighting efficiency an important consideration for sustainable basil production. Increasing light intensity can improve basil biomass and marketability, but it can also increase electricity consumption [7]. Higher daily light integral (DLI) can similarly promote biomass production and phytochemical accumulation, although the response depends on the light level and production conditions [28,29]. These findings indicate that greater light input does not necessarily result in proportional gains in production efficiency [7,28]. Light-use efficiency also varies among basil cultivars and across different lighting intensities [7,22]. Therefore, the reviewed evidence supports evaluating lighting strategies using biomass production, light-use efficiency, and energy demand rather than maximizing light input alone [7,28].

Overall, the reviewed evidence shows that basil responses to artificial lighting are strongly context dependent [15,22]. Light quantity and spectral composition can affect biomass, morphology, phytochemical composition, and volatile profiles, but the magnitude of these responses varies among cultivars and production conditions [7,22,25]. DLI and spectral composition should therefore be considered together when evaluating lighting strategies for basil production [15,28]. Recent studies also show that changes in spectral quality can modify phytochemical and sensory traits without necessarily reducing biomass [16,25,30]. Thus, no single lighting treatment can be assumed to maximise biomass, quality, and energy-use efficiency across all basil production systems [7,15,30]. Table 1 summarizes representative primary experimental studies examining the effects of light spectrum, PPFD, DLI, and photoperiod on Ocimum basilicum L. under controlled-environment and supplemental-lighting conditions.

3.2. Integrated Effects of LED Spectral Composition on Basil Growth, Morphology, and Phytochemical Accumulation

Spectral composition is a major control variable in plant factory systems with artificial lighting because LEDs allow specific wavelength ranges to be adjusted with high precision [22,23,37]. In Ocimum basilicum L., changes in spectral composition can modify biomass production, plant architecture, photosynthetic performance, essential-oil composition, and secondary metabolite accumulation [22,27,37]. These responses are mediated by several photoreceptor systems, including phytochromes, cryptochromes, phototropins, and UVR8, which connect light perception with photosynthesis, stomatal regulation, plant architecture, and secondary metabolism [48,49,50]. Recent experimental evidence in basil further shows that different LED wavelengths can alter photosynthetic efficiency, photoinhibition, and the accumulation of phenolic and flavonoid compounds [45]. Thus, spectral composition should be considered not only as a source of photosynthetically active photons, but also as a regulatory signal that influences the balance between vegetative growth and phytochemical production in basil [37,45].

Red light is an important component of LED lighting because it contributes strongly to photosynthetic carbon assimilation and vegetative growth in basil [22,23,31]. Red-enriched lighting can promote leaf expansion, shoot growth, and biomass accumulation, particularly when plants are grown under sufficient overall light intensity [23,51]. However, the response to red light depends on the presence of other wavelengths and on the overall lighting regime [22,31,36]. In basil, different red-to-blue and red-to-green combinations can produce distinct responses in growth and photosynthetic performance, with cultivar differences further modifying these effects [22,36]. Red-dominant treatments therefore do not consistently provide the highest biomass or physiological performance across cultivars and lighting conditions [36,52]. Red light should consequently be considered an important driver of vegetative growth, but its effects should be interpreted in relation to spectral balance, cultivar, and the broader lighting environment rather than red-light intensity alone [22,31,36].

Blue light has important regulatory effects on basil morphology, photosynthetic performance, and secondary metabolism [22,36,37]. Higher blue-light fractions can produce more compact plants and alter leaf morphology, although the magnitude of these responses depends on cultivar and the accompanying wavelengths [22,36]. Blue enrichment can also modify photosynthetic performance, but higher blue fractions do not necessarily increase carbon assimilation or biomass production [45,52]. Recent experiments show that blue light can increase phenolic and flavonoid accumulation in basil, indicating that spectral quality can influence secondary metabolism as well as growth [37,45]. However, these responses are not uniform across cultivars or metabolic traits. Changes in spectral composition can increase some phenolic compounds while altering volatile phenylpropanoids and terpenoids in different directions [37]. Blue light may therefore provide advantages for nutritional and phytochemical quality, but high blue-light exposure can also reduce photosynthetic assimilation and promote earlier photoinhibition under some conditions [45]. The production value of blue-light enrichment therefore depends on the target trait, cultivar, and overall lighting regime rather than on blue-light proportion alone [22,37,45].

Red-blue combinations are widely used in indoor basil production because they combine the strong photosynthetic contribution of red light with the regulatory effects of blue light [22,33]. In basil, mixed red-blue spectra can improve growth and physiological performance compared with some monochromatic treatments, but the response depends on spectral ratio, PPFD, cultivar, and growing conditions [22,36]. Lin et al., (2021) reported higher photosynthetic capacity and quantum yield under a 4:1:1 red:green:blue treatment than under 2:1:1 or 1:1:1 treatments in both green and purple-leaved basil. However, this result should not be interpreted as evidence for a universal optimal red-blue ratio because other studies have reported different responses under different experimental conditions [21,22]. In a controlled indoor experiment, d’Aquino et al., (2022) found that white light produced greater biomass than a blue-red treatment, whereas the blue-red treatment resulted in higher concentrations of several phenolic compounds [21]. Recent evidence further shows that changing the blue:red ratio can modify specific flavonoids and volatile compounds without necessarily changing basil biomass, and these responses can differ among cultivars [30]. Thus, red-blue mixtures should be evaluated as part of an integrated lighting regime rather than judged by a single preferred ratio, particularly when biomass, morphology, nutritional quality, and aroma are considered together [22,30,33,36].

Green light (500-600 nm) can penetrate deeper into leaves and dense canopies than red and blue light, allowing photons to contribute to photosynthesis in lower canopy layers [34]. In basil, this response can alter plant architecture and biomass production, but the direction and magnitude of the response depend on the spectral background [34,35]. Schenkels et al., (2020) reported greater leaf area, leaf number, stem length, and biomass when green light was added to the lighting regime, indicating a shade-avoidance response. In contrast, [35] found that including green wavelengths in red-blue treatments reduced shoot biomass in two O. basilicum cultivars under indoor vertical-farming conditions, while morphological responses differed between green and purple-leaved plants [35]. Recent physiological evidence further shows that green light can support high carbon assimilation in basil, with assimilation remaining relatively high under increasing green-light intensity [45]. Green light may therefore contribute to photosynthesis directly rather than acting only through changes in plant morphology [45,53]. However, its effects on biomass and quality are not uniform, as responses vary with cultivar, background spectrum, canopy structure, and production environment [32,34,35]. Therefore, green light should be considered a complementary component of basil lighting rather than a universally beneficial replacement for red-blue spectra [32,34,35].

Far-red (FR) radiation (700-800 nm) regulates basil architecture mainly through phytochrome-mediated signalling and changes in the red-to-far-red ratio [54]. In basil, FR supplementation generally promotes stem and leaf elongation, which can increase canopy spread and light interception but may reduce plant compactness [22]. Recent experiments confirm this response, with FR increasing stem elongation and biomass in both green and purple-leaved basil grown under controlled conditions [16]. However, greater biomass under FR does not necessarily indicate improved production quality, because excessive elongation can reduce compactness and alter marketable plant form [16,17]. FR can also influence stomatal behaviour and water use; [54] found that FR increased stomatal opening and evapotranspiration in sweet basil without increasing photosynthetic rate under the tested base-light intensity. Far-red photons may nevertheless enhance photosynthetic efficiency when combined with shorter wavelengths through the Emerson enhancement effect, although the response depends on the accompanying spectrum and total light intensity [50]. Evidence from supplemental-lighting experiments further shows that FR can modify basil biomass and essential-oil production when combined with red, blue, and green wavelengths, indicating that its effects cannot be separated from the broader spectral background [38]. Therefore, FR should be treated as a controlled spectral component that can improve canopy development and selected quality traits, while its intensity and red-to-far-red ratio must be managed to avoid excessive elongation and unnecessary water or energy use [16,17,54].

Ultraviolet (UV) radiation can influence both growth and secondary metabolism in basil [39,40]. The response depends on wavelength and exposure dose [39,41]. In sweet basil, supplemental UV-A and UV-B altered leaf growth, pigments, antioxidant-related compounds, and essential-oil composition [39]. These findings suggest that UV radiation can act as a developmental signal and a metabolic elicitor [39]. However, UV-A does not always reduce plant performance. Vodnik et al., (2023) found no clear growth or photosynthetic penalty in green basil exposed to 365 and 385 nm UV-A. Some treatments even enhanced photochemical activity and UV-protective responses [40]. Responses also differed between green and purple-leaved basil, showing a clear genotype effect [41]. In microgreens, UV-containing light treatments increased total phenolics and rosmarinic acid, although the specific contribution of UV could not be separated from the other wavelengths used [55]. Overall, UV responses in basil are highly context dependent. Wavelength, dose, exposure period, cultivar, developmental stage, and background spectrum can all modify the outcome [39,40,41,55]. UV-A and UV-B should therefore be viewed as targeted supplements for modifying basil quality rather than as reliable tools for increasing biomass alone [39,40,41].

Cultivar strongly influences how basil responds to LED lighting [22,56]. Green and purple-leaved basil can show different responses under the same spectral treatment [36,56]. These differences extend to biomass, leaf morphology, photosynthetic performance, and antioxidant-related traits [36,56]. Delgadillo-Narr et al. (2026) found that green basil produced greater biomass under some red:blue ratios, whereas purple basil showed stronger responses in bioactive compounds. Growth stage also affected the response, with spectral differences becoming more pronounced as plants developed [46]. The production environment adds another layer of variation. In a closed-type plant factory, ‘Amethyst Improved’ basil showed marked differences in biomass and morphology among LED treatments at a fixed PPFD and photoperiod [57]. By contrast, greenhouse-grown basil receives a changing solar background, which can modify the effect of supplemental LEDs [19]. Light quantity also interacts with this context, as different PPFD and photoperiod combinations produced different basil responses even when DLI was kept constant [15]. Therefore, spectral effects should be interpreted together with cultivar, developmental stage, PPFD, photoperiod, and production environment rather than as responses to wavelength alone [15,19,22].

Overall, basil responses to LED spectral composition are highly context dependent [11,22]. Red and blue light strongly influence photosynthesis, growth, and plant development, while green, far-red, and ultraviolet light can modify canopy structure, morphology, and secondary metabolism [35,39,54]. However, no single red:blue ratio consistently maximizes biomass and phytochemical quality across basil cultivars and growing conditions [21,30,36]. Spectral effects also depend on PPFD, photoperiod, and DLI, so the same spectrum can produce different responses under different light exposures [15,22]. Cultivar and developmental stage further influence these responses, as shown by differences between green and purple basil [46,56]. The production environment is also important because PFALs provide controlled lighting, whereas greenhouse supplementation interacts with natural sunlight [19,57]. Lighting strategies should therefore reflect the production objective, whether the priority is biomass, phytochemical quality, plant form, or energy efficiency [7,16]. Taken together, the evidence supports an integrated approach that considers spectrum, PPFD, photoperiod, DLI, cultivar, developmental stage, and production environment rather than a universal lighting recipe [15,22,30]. The integrated relationships between LED spectral components and key basil growth, morphological, and phytochemical responses are summarized in Figure 3.

3.3. Light Intensity Optimization, Daily Light Integral, and Energy-Use Efficiency in Basil Production

Photosynthetic photon flux density (PPFD) and daily light integral (DLI) describe different aspects of light availability in controlled-environment production [11,58]. PPFD measures the instantaneous flux of photosynthetically active photons reaching a given surface and is expressed in µmol m⁻² s⁻¹ [58]. DLI represents the cumulative amount of photosynthetically active photons received over a 24-h period and is expressed in mol m⁻² d⁻¹ [11,59]. Thus, PPFD describes the intensity of light at a given time, whereas DLI describes the total photon exposure accumulated during the day [5,58]. Both measures are important because the same DLI can be achieved through different combinations of PPFD and photoperiod [15,33]. These combinations do not necessarily produce the same physiological response in basil, even when total daily photon exposure is similar [15,18]. Eghbal et al., (2024), for example, maintained a DLI of 12.96 mol m⁻² d⁻¹ while varying PPFD from 200 to 400 µmol m⁻² s⁻¹ and adjusting the photoperiod accordingly, and observed different growth and phytochemical responses among treatments. Similar evidence from sweet basil showed that 16 and 24-h lighting regimes produced different quality responses despite maintaining the same DLI of 12.7 mol m⁻² d⁻¹ [18]. Therefore, basil lighting studies should report both PPFD and DLI, because cumulative photon supply alone does not fully describe the biological effects of a lighting regime [11,15,33].

PPFD directly influences photosynthetic activity and biomass accumulation in basil [7,22,60]. Increasing PPFD generally increases fresh and dry biomass when light availability is limiting, although the magnitude of the response varies among cultivars [7,22]. Pennisi et al., (2020) observed progressive increases in basil biomass as PPFD increased from 100 to 250 µmol m⁻² s⁻¹ under red-blue LEDs, while a further increase to 300 µmol m⁻² s⁻¹ produced no additional yield gain. This response indicates that biomass does not necessarily increase linearly with increasing photon supply. Recent evidence also shows that higher PPFD can continue to increase biomass under some conditions. d’Aquino et al., (2024a) reported greater fresh and dry biomass at 380 µmol m⁻² s⁻¹ than at 250 µmol m⁻² s⁻¹ under white light, showing that the response can extend beyond the range reported by [60]. However, increasing light intensity does not always improve light-use efficiency to the same extent as biomass, because additional photons can provide smaller gains once plants approach their photosynthetic capacity [7,22]. Akter et al. (2026) further showed that dynamic increases in light intensity from 200 to 400 µmol m⁻² s⁻¹ improved dry biomass and light-use efficiency when light delivery was progressively adjusted during crop development. Therefore, the biomass response to PPFD should be interpreted as a context-dependent response rather than a fixed linear relationship, with cultivar, spectrum, developmental stage, photoperiod, and DLI influencing the point at which additional light produces smaller returns [15,22,47,62].

Daily light integral (DLI) provides a measure of cumulative photon exposure and is closely related to biomass production in basil [11]. Increasing DLI generally improves biomass when light is limiting, but the response is not proportional across all exposure levels [29,60]. Dou et al., (2018) reported greater biomass and improved nutritional traits as DLI increased, with a DLI of 12.9 mol m⁻² d⁻¹ identified as a practical compromise between yield, quality, and energy demand under the conditions tested. However, this value should not be treated as a universal threshold because basil responses differ with PPFD, photoperiod, cultivar, and production stage [15,22]. Ciriello et al., (2023) compared DLI values of 7.5 and 15 mol m⁻² d⁻¹ in Genovese basil and found that the higher DLI improved yield during the first harvest but did not consistently increase fresh biomass after the second harvest. The higher DLI also reduced incident light-use efficiency at the first harvest, showing that greater biomass does not necessarily correspond to greater efficiency [28]. Pennisi et al., (2020) similarly showed that increasing PPFD from 250 to 300 µmol m⁻² s⁻¹, corresponding to an increase in DLI from 14.4 to 17.3 mol m⁻² d⁻¹, produced no further basil yield increase under their red–blue lighting regime. These contrasting results indicate that DLI can explain part of the variation in basil productivity, but simple DLI thresholds cannot reliably predict biomass across different lighting regimes and production conditions [15,28,29].

DLI can be achieved through different combinations of PPFD and photoperiod, but these combinations do not necessarily produce the same response in basil [15,18]. Eghbal et al., (2024) maintained a DLI of 12.96 mol m⁻² d⁻¹ while comparing 200, 300, and 400 µmol m⁻² s⁻¹ at 18, 12, and 9 h of lighting, respectively, and found better biomass and phytochemical responses under the lower-intensity, longer-duration treatments. The 400 µmol m⁻² s⁻¹ treatment with a 9-h photoperiod produced poorer growth and antioxidant activity, despite receiving the same daily photon dose [15]. Puccinelli et al., (2025) similarly maintained a DLI of 12.7 mol m⁻² d⁻¹ and found no significant difference in basil growth between 16-h and continuous 24-h lighting, although continuous lighting increased several leaf-quality traits. Evidence from successive-harvest experiments further shows that longer photoperiods can improve basil yield after cutting, while having little effect on uncut plants [28]. These findings indicate that photoperiod can modify the biological response to a given DLI, particularly when crop developmental stage is considered [15,28]. From an energy perspective, distributing the same DLI over a longer photoperiod does not necessarily reduce total lighting electricity use, although lower PPFD can reduce peak electrical demand and heat generation [9,15]. In another indoor basil study, intermittent lighting with a shorter photoperiod maintained biomass and quality while offering opportunities to reduce energy demand and shift lighting operation to periods with lower electricity prices [63]. Therefore, photoperiod should be considered as a separate management variable rather than simply a means of achieving a target DLI, because its effects on biomass, quality, and energy performance depend on PPFD, developmental stage, lighting schedule, and electricity conditions [15,18,28,63].

Artificial lighting is a major energy input in PFALs. Therefore, increases in DLI should be evaluated against the biomass gained from the additional light [7,9]. Higher DLI can increase basil biomass, but gains may become smaller as light availability increases [29,60]. Pennisi et al., (2020) reported increasing biomass as PPFD increased from 100 to 250 µmol m⁻² s⁻¹, whereas 300 µmol m⁻² s⁻¹ produced no further yield increase under their red-blue LED treatment. Ciriello et al., (2023) similarly found that increasing DLI from 7.5 to 15 mol m⁻² d⁻¹ increased first-harvest yield but reduced incident light-use efficiency. The yield advantage was less consistent after the second harvest [28]. In greenhouse-grown Genovese basil, Hammock et al. (2023) also found large differences in biomass efficiency among supplemental-lighting treatments, showing that additional electrical input does not always produce proportional biomass gains. Thus, DLI should be evaluated using biomass production, light-use efficiency, electricity consumption, and yield gained per unit of energy supplied [9,28,42].

Light quantity also affects basil phytochemical quality, but its effects are not always proportional to biomass production [15,29]. Increasing light exposure can modify phenolic compounds, flavonoids, antioxidant activity, and essential-oil production [43,64]. However, these responses depend on cultivar, spectrum, and the distribution of light over the day [15,43]. Eghbal et al., (2024) maintained the same DLI of 12.96 mol m⁻² d⁻¹ while changing PPFD and photoperiod, and observed different phytochemical responses among treatments. Eskandarzade et al., (2024) also found that light intensity affected phenolic compounds, flavonoids, antioxidant activity, and essential-oil content and yield in green and purple basil. These results show why phytochemical concentration should be distinguished from total phytochemical yield, because concentration does not account for differences in biomass production [43]. Light quantity also interacts with spectral composition, so the same DLI can produce different quality responses under different spectra [30,37]. Marter et al., (2026) found cultivar and compound-specific changes in flavonoids and volatile compounds across blue:red spectral treatments, while basil biomass remained relatively stable. Recent evidence further confirms this interaction, with far-red and UV-A producing different phytochemical responses at different light intensities in indoor-grown basil [65]. Therefore, DLI should be evaluated together with spectral composition and biomass when assessing basil phytochemical quality [15,30,65].

The response of basil to light quantity also depends on spectral composition and cultivar [7,22]. Increasing PPFD does not produce the same response under all spectra because wavelength composition can alter how plants use additional photons [15,24]. Farhangi et al., (2025) found that increasing PPFD from 122 to 244 µmol m⁻² s⁻¹ increased biomass in ‘Emily’ basil, while deep-red and far-red supplementation produced different effects on leaf number, canopy size, and biomass at similar PPFD. This finding shows that light quantity and spectral quality should not be evaluated separately. Cultivar adds another source of variation because basil genotypes differ in growth, photosynthetic capacity, morphology, and phytochemical responses to the same lighting conditions [7,22,56]. Recent spectral-gradient experiments further showed that blue:red ratios produced cultivar and compound-specific phytochemical responses while biomass remained relatively stable [30]. Delgadillo-Narr et al. (2026) similarly found different responses between green and purple basil, with spectral effects becoming more pronounced as plants developed. DLI can also interact with the growing environment. Walters et al., (2023) showed that DLI effects on basil growth and leaf colour changed with mean daily temperature, demonstrating that higher light availability does not produce a fixed response across conditions. These findings support cultivar and stage-specific lighting strategies rather than a single PPFD, DLI, or spectral recipe for all basil production systems [15,24].

Overall, basil lighting should be optimized according to the production objective rather than by maximizing light input alone. Higher PPFD or DLI can increase biomass, but additional yield may not justify the associated energy demand [7,28]. Light-use efficiency can also decline when light is increased beyond the range that supports efficient biomass production [28,60]. Zhou et al. (2022) demonstrated this trade-off in Genovese basil, where different blue:red ratios favoured leaf biomass, resource-use efficiency, or flavour-related volatiles. The most suitable lighting treatment therefore depends on whether the production goal is yield, quality, resource efficiency, or a combination of these traits. Intermittent lighting can also reduce the energy footprint while maintaining basil growth under some controlled-environment conditions [68]. Therefore, commercial lighting strategies should consider biomass gain per unit of electricity, product quality, and production time together with PPFD, DLI, photoperiod, spectrum, and cultivar [28,67,68]. No single PPFD, DLI, photoperiod, or spectral combination can be considered optimal for all basil production systems. Lighting should instead be adjusted to cultivar, developmental stage, production environment, and market objective [15,24,30]. The conceptual relationship between light input, basil biomass accumulation, and energy-use efficiency is summarized in Figure 4.

3.4. Consensus and Contradictions in Basil Lighting Research

Across the reviewed studies, the clearest consensus is that basil responses to lighting depend on both spectral composition and light quantity. Red-blue combinations can support strong biomass production and photosynthetic performance, but responses vary with cultivar, PPFD, photoperiod, and spectral ratio [22,36,60]. Recent evidence also challenges the use of a single red:blue ratio as an optimum for basil production. Marter et al. (2026) found relatively stable biomass across a wide blue:red gradient, while phytochemical responses differed among cultivars and compounds. Blue light can increase phenolic and flavonoid accumulation, but high blue-light exposure may also reduce photosynthetic assimilation and increase photo-inhibition [45]. UV-A responses are also dependent on wavelength and intensity [40,41]. Light quantity interacts with spectral quality as well. Changes in PPFD and photoperiod can alter basil responses even when DLI is similar [15,18]. The strongest consensus is therefore not a specific lighting recipe. It is the need to evaluate spectrum, PPFD, photoperiod, DLI, cultivar, and production objective together [15,30,45].

A major area of context dependence in basil lighting research concerns the relationship between biomass and phytochemical quality. Some studies report greater biomass under red-rich or higher-light treatments, whereas others report higher concentrations of selected phenolics, flavonoids, or antioxidant compounds under different spectra [15,23,64]. However, these responses do not always indicate a direct trade-off. In Genovese basil, different blue:red ratios favoured different combinations of leaf biomass, resource-use efficiency, and flavour-related volatiles [67]. Supplemental LED treatments also altered polyphenol and volatile profiles without significantly changing biomass in green and red-leafed basil [25]. Recent evidence further shows that blue:red spectral gradients can modify flavonoids and volatile compounds while biomass remains relatively stable [30]. Light intensity can also affect both productivity and phytochemical composition, although responses differ between green and purple basil [43]. Similarly, LED lighting improved several nutritional traits while maintaining or improving yield in hydroponically grown Genovese basil, although the response differed between cultivars [69]. These findings indicate that biomass and phytochemical quality should be evaluated as separate but interacting production outcomes. Their relationship depends on spectrum, light intensity, cultivar, developmental stage, and the specific quality trait being measured [15,30,43].

Green light remains one of the most debated components of basil lighting. Green photons penetrate deeper into leaves and can reach lower canopy layers than red and blue photons [34,50,53]. However, greater penetration does not always increase basil biomass. Schenkels et al. (2020) reported greater biomass, leaf area, and stem elongation after green-light supplementation, whereas Dou et al. (2020) found cultivar-dependent responses under red-green-blue lighting. Lauria et al. (2023) further showed that supplemental LED lighting could modify polyphenol and volatile profiles without significantly changing biomass. Recent physiological studies provide further evidence that green light can contribute directly to photosynthesis. Jokic et al. (2025) reported high CO₂ assimilation under green light, while Pappert et al. (2025) found that red light produced the highest CO₂ assimilation in basil under their experimental conditions. More recent evidence shows that wavelengths within the green region can produce high photosynthetic rates under high irradiance, although responses varied with wavelength and leaf position [71]. These contrasting results indicate that the value of green light depends on irradiance, spectral background, cultivar, canopy structure, and developmental stage. Green light should therefore be considered a complementary component of basil lighting rather than a universal replacement for red-blue spectra.

3.5. Integrated Lighting Optimization Framework for Basil Production in PFAL Systems

The evidence reviewed in Section 3.2, Section 3.3 and Section 3.4 shows that basil responses to artificial lighting cannot be explained by spectral composition, PPFD, or DLI alone. These factors interact with photoperiod, cultivar, and developmental stage to influence growth, morphology, phytochemical accumulation, and energy-use efficiency [15,21,22]. The same daily photon dose can produce different responses when delivered at different PPFDs and photoperiods [15,18]. Spectral composition can also alter the balance between biomass production and secondary metabolism [30,45]. Cultivar further modifies these responses, as shown by differences among green and purple basil genotypes under similar lighting conditions [22,46]. Recent evidence also shows that photoperiod can affect phytochemical profiles differently among basil genotypes [44]. These findings support an integrated approach in which light quality, light quantity, cultivar, growth stage, and production objective are considered together. Based on these interactions, Figure 5 presents an integrated framework for linking lighting inputs, biological factors, crop responses, and production objectives in PFAL basil production.

Drawing on the reviewed experimental evidence, Table 2 summarises evidence-informed LED lighting strategies for different basil production objectives in PFAL systems. The strategies integrate spectral composition, PPFD, DLI, photoperiod, cultivar, developmental stage, crop responses, and energy-use considerations. The reported ranges are intended as practical evidence boundaries rather than universal lighting prescriptions.

The interaction between spectral composition and DLI is important because basil does not respond to photon quantity independently of wavelength. The same DLI can produce different responses when the spectral composition changes [11,22,29]. Red-blue spectra can support strong biomass production under moderate DLI, but the response depends on the red:blue ratio, cultivar, and light intensity [22,33]. In contrast, increasing the proportion of blue light can alter photosynthetic performance and stimulate phenolic and flavonoid accumulation without necessarily increasing biomass [37,64]. Recent evidence further shows that light intensity and spectral composition interact at the physiological level. Jokic et al. (2025) found that photosynthetic assimilation differed among blue, green, red, and white light, while blue light promoted greater phenolic and flavonoid accumulation. This indicates that additional photons are not used in the same way under all spectra. Spectral composition can influence the balance between carbon assimilation, growth, and secondary metabolism [30,45]. Therefore, DLI should be evaluated together with spectral composition when assessing basil productivity and quality. Rather than defining a single DLI for each spectrum, future lighting strategies should consider the combined effects of spectrum, PPFD, cultivar, and production objective.

Yield, quality, and energy use are closely linked but should not be treated as identical outcomes. Increasing light input can increase basil biomass, but the response depends on cultivar, spectrum, PPFD, and production conditions [7,29]. Tabbert et al. (2022) found that higher light intensity increased growth and marketability, but biomass efficiency differed among basil cultivars. Quality responses can follow a different pattern, blue-enriched lighting can increase phenolic and flavonoid concentrations without a corresponding increase in biomass [45,64]. Spectral changes can also alter volatile compounds and flavour-related traits [16,67]. Zhou et al., 2022) showed that different blue:red ratios favoured different combinations of yield, resource-use efficiency, and flavour in Genovese basil. Energy use adds another dimension. Higher light input increases electricity demand, but biomass gain does not necessarily increase at the same rate [7,42]. Hammock et al. (2023) found substantial variation in light-use efficiency among supplemental-lighting treatments in greenhouse-grown basil. YANG Yang, (2024) also showed that green:blue ratios affected basil growth and energy-use efficiency differently. These findings show that lighting decisions involve several outcomes rather than yield alone. A treatment may increase biomass but require more electricity. Another may improve quality with little change in biomass. Therefore, basil lighting should be evaluated using yield, quality, electricity consumption, and light-use efficiency together [42,67,74].

Cultivar and developmental stage are important modifiers of basil responses to LED lighting. Basil genotypes differ in growth, morphology, photosynthetic capacity, and phytochemical responses under the same lighting conditions [7,22,56]. Green and purple basil can therefore respond differently to the same spectrum [36,56]. Delgadillo-Narr et al. (2026) found different spectral responses between green and purple basil. The differences were observed in both biomass and bioactive compounds. Spectral effects also became more pronounced as plants developed [46]. Rihan et al. (2020) further demonstrated that the response of sweet basil to LED spectrum depended on the lighting recipe used in a plant-factory system. Knyazeva et al. (2025) reported clear cultivar-specific responses in green ‘Tonus’ and purple ‘Ararat’ basil. Red lighting increased leaf number, leaf area, biomass, and productivity across the tested treatments. Blue lighting produced stronger responses in selected phytochemicals and essential oil traits, but the magnitude differed between cultivars and lighting periods [72]. These findings show that cultivar and timing of light exposure can modify basil responses to LED treatments. The same spectrum may therefore produce different outcomes at different stages of crop development. Lighting strategies should consequently consider cultivar and developmental stage together with spectrum, PPFD, DLI, and photoperiod [15,44,46]. Further experiments are needed to determine when stage-specific or dynamic lighting provides consistent advantages over fixed lighting regimes.

Practical optimization of basil lighting should begin with the production objective. The main targets may be biomass, quality, aroma, essential oils, or energy efficiency [67,69]. These targets do not always require the same lighting conditions. Red-blue or broadband spectra can provide a useful baseline for biomass production [22,30]. Additional wavelengths can then be introduced when specific quality traits are targeted [30,76]. PPFD and photoperiod should be adjusted to achieve the required DLI. A higher DLI should not be assumed to produce a proportional increase in yield [15,28]. Cultivar and growth stage should also be considered because basil genotypes can respond differently to the same lighting treatment [46,72]. Recent work shows that gradual changes in light intensity and photoperiod can improve dry biomass and light-use efficiency under comparable DLI conditions [47]. Real-time physiological feedback provides another option for optimization. Stevens et al. (2026) used chlorophyll-fluorescence feedback to adjust light intensity according to basil demand. The approach increased yield per unit power and reduced energy use per unit fresh mass [77]. Targeted UV-B exposure can also modify basil quality traits, but the response depends on dose and exposure duration [76]. Practical optimization should therefore be treated as an adaptive process rather than the selection of one fixed lighting recipe. The final strategy should balance biomass, quality, production time, and electricity use.

3.6. Implications for Sustainable Indoor Basil Production

Lighting efficiency is central to sustainable basil production in PFAL systems. Artificial lighting is one of the major energy inputs in indoor production [6,7]. Increasing PPFD can increase basil biomass, but it also increases electricity demand [7]. Higher DLI does not always produce proportional gains in biomass or energy-use efficiency [28,29]. Recent basil research confirms that energy performance varies among DLI regimes [9]. Therefore, lighting should be evaluated using both crop productivity and energy use. Yield per unit of electricity provides a useful indicator for comparing lighting strategies [9]. Sustainable PFAL production should therefore focus on efficient light delivery rather than simply increasing light input.

Spectral management should be aligned with the production objective. Red-blue and broadband spectra can support basil biomass production, but quality responses vary with cultivar and spectral composition [22,30]. Blue enrichment can increase phenolic and flavonoid accumulation, although high blue-light exposure may reduce photosynthetic performance under some conditions [45]. Red and far-red treatments can also modify phytochemical composition and biomass allocation when applied at specific periods [78]. Therefore, spectrum selection should consider the intended balance among yield, nutritional quality, aroma, and energy use rather than a single preferred spectral ratio.

System-level optimization can further improve the energy efficiency of PFALs. Reflective materials can reduce lighting energy demand while maintaining or improving crop growth [79]. Solar-assisted lighting and improved light-management strategies can also reduce energy consumption, although their benefits depend on system design and environmental conditions [80]. Energy efficiency therefore depends on the combined optimization of lighting, environmental control, and energy supply rather than LED performance alone [79,81]. Future basil PFAL studies should evaluate these components together to identify energy-efficient production strategies.

Scalable PFAL production requires crop-specific lighting and efficient use of growing space. Planting density can strongly affect light interception, yield, and light-use efficiency in vertical basil production [82]. Spectral adjustments can further improve biomass and canopy development under controlled conditions, although responses depend on the lighting regime [24]. Practical PFAL systems should therefore integrate planting density, spectral management, and energy efficiency rather than rely on a fixed lighting recipe.

3.7. Research Gaps and Future Directions

Despite growing evidence, research on basil lighting remains fragmented. Many studies examine individual factors such as spectrum, PPFD, photoperiod, or DLI under different experimental conditions [9,11,28]. Recent studies have also examined spectral manipulation and resource efficiency in vertical systems, but these variables are rarely evaluated together [24,30]. This limits direct comparison among studies and makes it difficult to develop broadly applicable lighting strategies for commercial PFAL basil production.

A major gap is the limited use of multifactorial experiments that combine spectral composition, PPFD, and DLI. These variables interact, so changing one while holding the others constant may not capture the full basil response [15,22,28]. Recent studies show that the same DLI can produce different growth and phytochemical responses when PPFD, photoperiod, or spectral composition changes [15,45]. Future studies should therefore test spectrum × PPFD × DLI interactions under standardized PFAL conditions to develop more reliable, cultivar-specific lighting strategies.

Reliable cultivar-specific DLI benchmarks are still lacking for basil. Reported responses to DLI vary with cultivar, PPFD, photoperiod, temperature, and developmental stage [15,22,28,66]. Recent studies further show that different basil genotypes can respond differently to the same light environment [30,46]. Future research should therefore establish cultivar and stage-specific DLI ranges under standardized PFAL conditions rather than a single universal threshold.

Cultivar-specific variation remains insufficiently characterized in PFAL basil research. Basil genotypes can differ in biomass, morphology, photosynthetic performance, and phytochemical responses under the same lighting conditions [22,46,56]. High-throughput phenotyping can help capture these genotype × light interactions using non-destructive imaging, spectral sensing, and chlorophyll-fluorescence measurements [40,83]. Integrating these tools with automated lighting control could support more precise, cultivar-specific lighting strategies in PFALs.

Energy and environmental performance remain underreported in basil PFAL studies. Most experiments emphasize biomass and quality, while few quantify electricity use, production cost, or environmental impacts alongside crop performance [7,9,29]. Recent life-cycle studies show that electricity demand can be a major environmental hotspot in vertical farming, while the impact varies with the electricity source [84,85]. Future studies should therefore combine yield, energy use, production cost, and environmental indicators to identify lighting strategies that are both productive and resource-efficient.

Dynamic and adaptive lighting remains an important research gap in PFAL basil production. Recent basil studies show that gradually changing light intensity and photoperiod can improve dry biomass and light-use efficiency under comparable DLI conditions [47], while real-time chlorophyll-fluorescence feedback can improve yield per unit power and reduce energy use [77]. Future studies should test stage-specific, sensor-driven lighting under standardized PFAL conditions to determine when dynamic strategies provide consistent advantages over fixed regimes.

The molecular mechanisms underlying basil responses to light remain insufficiently resolved. Recent multi-omics studies show that light quality can alter gene expression and metabolite pathways associated with secondary metabolism, including phenylpropanoid and terpenoid biosynthesis (Li et al., 2025). Metabolomic studies also show that light intensity and DLI interact with environmental conditions to modify rosmarinic acid, volatile compounds, and other metabolites [88]. Future research should integrate transcriptomics, metabolomics, and physiological measurements to link specific light treatments with metabolic responses in O. basilicum and support mechanism-based lighting strategies.

Commercial validation of basil lighting strategies remains limited. Most studies are conducted under tightly controlled conditions, whereas commercial PFALs must also consider planting density, electricity use, production costs, and marketable quality [82,89]. Recent basil studies show that lighting and crop density can improve resource-use efficiency, but these responses need validation at larger production scales [18,82]. Future studies should therefore combine crop performance, energy use, economics, and product quality in pilot- and commercial-scale PFAL trials. This directly addresses the current manuscript gap that experimental findings may not fully represent commercial production conditions.

4. Discussion Conclusions and Recommendations

This review shows that LED lighting strongly influences basil production in plant factory systems with artificial lighting (PFALs). However, basil responses depend on more than spectral composition or DLI alone. PPFD, photoperiod, cultivar, growth stage, and production conditions also influence crop responses. No single lighting recipe can therefore be considered optimal for all basil production systems.

Efficient basil production requires an integrated lighting approach. Spectral composition should be selected according to the production objective. PPFD and photoperiod should be coordinated to achieve an appropriate DLI. Lighting should also account for cultivar and growth stage. Biomass, quality, and energy-use efficiency should be evaluated together.

A major research gap is the limited integration of these factors in multifactorial PFAL experiments. Future studies should test spectrum, PPFD, DLI, and photoperiod together. Cultivar- and stage-specific lighting ranges should also be established. Consistent reporting of light conditions, crop responses, planting density, and electricity use would improve comparisons among studies.

Future research should also examine dynamic and sensor-based lighting strategies under realistic production conditions. These approaches should be evaluated using crop yield, quality, energy use, and economic performance. Pilot- and commercial-scale validation is needed. Such work can support practical, cultivar-specific, and energy-efficient lighting strategies for sustainable basil production in PFALs.