*2.1. Phenological Analysis*

*Arabidopsis thaliana* plants grown with 120 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> under the HPS light type (control) completed their life cycle, from sowing to the fruit ripening and senescence phenological stage, in 57 days (dark green solid line in Figure 1). Plants delayed their life cycle completion when growing with lower light intensity (Figure 1). In particular, life cycle duration was inversely related to light intensity (dashed lines). This delay was even wider during the reproductive phase (bolting to ripening stage). Although a similar delay can be observed between control (HPS) and treated plants (CoeLux®), the latter plants showed a higher magnitude for all light intensities considered. Significant differences between plants grown under the two different light types increased with the lowering of the light intensity, showing the smaller delay at 120 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> and the highest delay at 20 µmol m−<sup>2</sup> s −1 . Furthermore, at the lowest light condition (20 µmol m−<sup>2</sup> s −1 ), *A. thaliana* plants were unable to complete their life cycle with the production of ripe seeds, both under the HPS light type and the CoeLux® system's light type. In particular, under the CoeLux® light type, seeds were produced only at the highest light intensities (70 and 120 µmol m−<sup>2</sup> s −1 ). These seeds were viable and germinated regularly at 98% when sown (data not shown).

**Figure 1.** Phenological stages observation were recorded both under CoeLux® light (blue) and under HPS light (green) at four different light intensities, namely 20, 30, 70, and 120 μmol m−2s −1. Error bars represent the 95% confidence interval. **Figure 1.** Phenological stages observation were recorded both under CoeLux® light (blue) and under HPS light (green) at four different light intensities, namely 20, 30, 70, and 120 µmol m−<sup>2</sup> s −1 . Error bars represent the 95% confidence interval.

#### *2.2. Morphological Traits 2.2. Morphological Traits*

The biomass of both leaves and roots was found to increase with the increase of the light intensity (Figure 2a,b). The highest biomass values were measured for plants growing at 120 μmol m−2s −1, for both leaves (Figure 2a) and roots (Figure 2b) organs. For both leaves and roots biomass, significant differences between plants grown under the Coe-Lux® light type and plants grown under the HPS light type were measured at 20, 30, and 120 μmol m−2s −1 . The root biomass of plants grown at 20 μmol m−2s −1 and 30 μmol m−2s −1 was not measured due to the low weight, which was lower than the limit of the scale range (0.0001 g). The shoot/root ratio data (Figure 2c) were significantly higher in plants grown with 70 μmol m−2s −1. Moreover, at 120 μmol m−2s −1 , plants grown under the CoeLux® light type showed a significantly lower shoot/root ratio (Figure 2c). The biomass of both leaves and roots was found to increase with the increase of the light intensity (Figure 2a,b). The highest biomass values were measured for plants growing at 120 µmol m−<sup>2</sup> s −1 , for both leaves (Figure 2a) and roots (Figure 2b) organs. For both leaves and roots biomass, significant differences between plants grown under the CoeLux® light type and plants grown under the HPS light type were measured at 20, 30, and 120 µmol m−<sup>2</sup> s −1 . The root biomass of plants grown at 20 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> and 30 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> was not measured due to the low weight, which was lower than the limit of the scale range (0.0001 g). The shoot/root ratio data (Figure 2c) were significantly higher in plants grown with 70 µmol m−<sup>2</sup> s −1 . Moreover, at 120 µmol m−<sup>2</sup> s −1 , plants grown under the CoeLux® light type showed a significantly lower shoot/root ratio (Figure 2c).

The Projected Rosette Area (PRA) increased with the increase in light intensity independently of the light type analyzed (Figure 3a). The only exception was found for the CoeLux® light type, with no differences in PRA between 70 and 120 µmol m−<sup>2</sup> s −1 (Figure 3a). Plants grown under the HPS light type had significantly higher PRA values than plants grown under the CoeLux® light type, with the only exception at 70 µmol m−<sup>2</sup> s −1 (Figure 3a).

The diameter of the rosette (RD) increased with the increase in the light intensity independently of the light type analyzed (Figure 3b). Plants grown under both light types did not show significant differences in RD between 70 and 120 µmol m−<sup>2</sup> s −1 (Figure 3b). Plants grown under the HPS light type had significantly higher values of RD than plants grown under the CoeLux® light type with the only exception at 70 µmol m−<sup>2</sup> s −1 (Figure 3b).

**Figure 2.** (**a**) Leaves biomass (g), (**b**) root biomass (g), and (**c**) shoot-to-root ratio for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light type, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the The lamina to petiole ratio (L/P) increased with the increase in light intensity independently of the light type analyzed (Figure 3c). In the case of plants grown under the CoeLux® light type, similar values were measured between 20 and 30 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> and between 70 and 120 µmol m−<sup>2</sup> s −1 (Figure 3c). In the case of plants grown under the HPS light type, L/P values were similar between 70 and 120 µmol m−<sup>2</sup> s −1 . Plants grown under the HPS light type had significantly higher L/P values than plants grown under the CoeLux® light type only at 30 µmol m−<sup>2</sup> s −1 (Figure 3c).

−1. Moreover, at 120 μmol m−2s

type showed a significantly lower shoot/root ratio (Figure 2c).

*Plants* **2021**, *10*, x FOR PEER REVIEW 4 of 15

same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different

extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the

light (blue) and under HPS light (green) at

, plants grown under the CoeLux®

−1 and 30 μmol m−2s

−1

light

−1 (Figure

−1 (Figure 3b).

−1 (Figure

−1

−1. Error bars represent the 95% confidence interval.

−1, for both leaves (Figure 2a) and roots (Figure 2b) organs. For both

The biomass of both leaves and roots was found to increase with the increase of the light intensity (Figure 2a,b). The highest biomass values were measured for plants grow-

light type and plants grown under the HPS light type were measured at 20, 30, and

−1

leaves and roots biomass, significant differences between plants grown under the Coe-

was not measured due to the low weight, which was lower than the limit of the scale range (0.0001 g). The shoot/root ratio data (Figure 2c) were significantly higher in plants grown

. The root biomass of plants grown at 20 μmol m−2s

**Figure 1.** Phenological stages observation were recorded both under CoeLux®

*2.2. Morphological Traits*

ing at 120 μmol m−2s

−1

120 μmol m−2s

with 70 μmol m−2s

four different light intensities, namely 20, 30, 70, and 120 μmol m−2s

Lux®

median value, whereas the dotted horizontal line is the mean.

**Figure 2.** (**a**) Leaves biomass (g), (**b**) root biomass (g), and (**c**) shoot-to-root ratio for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light type, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the **Figure 2.** (**a**) Leaves biomass (g), (**b**) root biomass (g), and (**c**) shoot-to-root ratio for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light type, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations, and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean. The lamina to petiole ratio (L/P) increased with the increase in light intensity independently of the light type analyzed (Figure 3c). In the case of plants grown under the CoeLux® light type, similar values were measured between 20 and 30 μmol m−2s −1 and between 70 and 120 μmol m−2s −1 (Figure 3c). In the case of plants grown under the HPS light type, L/P values were similar between 70 and 120 μmol m−2s −1. Plants grown under the HPS light type had significantly higher L/P values than plants grown under the Coe-Lux® light type only at 30 μmol m−2s −1 (Figure 3c).

**Figure 3.** (**a**) Projected rosette area (cm<sup>2</sup> ), (**b**) rosette diameter (cm), and (**c**) lamina-to-petiole length ratio for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. The lamina-to-petiole length ratio is the mean of three leaves for each of the ten replicates. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean. **Figure 3.** (**a**) Projected rosette area (cm<sup>2</sup> ), (**b**) rosette diameter (cm), and (**c**) lamina-to-petiole length ratio for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. The lamina-to-petiole length ratio is the mean of three leaves for each of the ten replicates. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean.

#### *2.3. Physiological Measurements 2.3. Physiological Measurements*

The chlorophyll content increased with the increase in the light intensity, and no significant differences were detected between CoeLux® and control light (Figure 4a). In the case of plants grown under the CoeLux® light type, the highest chlorophyll concentrations were found in plants grown with a light intensity of 70 and 120 μmol m−2 , while the lowest concentrations were found for 20 and 30 μmol m−2 s −1, which did not differ from each other (Figure 4a). In the case of plants grown under the HPS light type, the highest and the lowest values were found for 120 and 20 μmol m−2 s −1, respectively (Figure 4a). The chlorophyll content increased with the increase in the light intensity, and no significant differences were detected between CoeLux® and control light (Figure 4a). In the case of plants grown under the CoeLux® light type, the highest chlorophyll concentrations were found in plants grown with a light intensity of 70 and 120 µmol m−<sup>2</sup> , while the lowest concentrations were found for 20 and 30 µmol m−<sup>2</sup> s −1 , which did not differ from each other (Figure 4a). In the case of plants grown under the HPS light type, the highest and the lowest values were found for 120 and 20 µmol m−<sup>2</sup> s −1 , respectively (Figure 4a).

The flavonoid content also increased with the increase in light intensity (Figure 4b). In the case of plants grown under the CoeLux® light type, the highest values were found for 70 and 120 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> and the lowest values for 20 µmol m−<sup>2</sup> s −1 (Figure 4b). In the case of plants grown under the HPS light type, the highest and the lowest values were

found for 120 and 20 µmol m−<sup>2</sup> s −1 , respectively (Figure 4b). A significant difference between plants grown under the CoeLux® and the HPS light type was observed only at 20 µmol m−<sup>2</sup> s −1 . and 120 μmol m−2 s −1. No significant difference was observed between plants grown under the CoeLux® and the HPS light type, independently of the light intensity considered (Figure 4c).

The flavonoid content also increased with the increase in light intensity (Figure 4b).

−1 and the lowest values for 20 μmol m−2 s

case of plants grown under the HPS light type, the highest and the lowest values were

tween plants grown under the CoeLux® and the HPS light type was observed only at 20

The anthocyanin concentration decreased with the increase in light intensity independently of the light type considered (Figure 4c). In the case of plants grown under the

light type, the highest and the lowest values were found for 20 and 30 μmol m−2

light type, the highest values were found

−1, respectively (Figure 4b). A significant difference be-

−1, respectively. In the case of plants grown under the HPS

−1 (Figure 4b). In the

−1 and the lowest values for 70

light type, the highest values were found for 20 μmol m−2 s

*Plants* **2021**, *10*, x FOR PEER REVIEW 5 of 15

In the case of plants grown under the CoeLux®

for 70 and 120 μmol m−2 s

−1 .

μmol m−2 s

CoeLux®

s

found for 120 and 20 μmol m−2 s

−1 and 70 and 120 μmol m−2 s

**Figure 4.** (**a**) Chlorophyll content (µg cm<sup>−</sup><sup>2</sup> ), (**b**) flavonols content (µg cm<sup>−</sup><sup>2</sup> ), and (**c**) anthocyanin content (µg cm<sup>−</sup><sup>2</sup> ) for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean. **Figure 4.** (**a**) Chlorophyll content (µg cm−<sup>2</sup> ), (**b**) flavonols content (µg cm−<sup>2</sup> ), and (**c**) anthocyanin content (µg cm−<sup>2</sup> ) for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean.

The maximum quantum efficiency of PSII photochemistry (*Fv*/*Fm*) increased with the increase in the light intensity independently of the light type considered (Figure 5a). In the case of plants grown under the CoeLux® light type, *Fv*/*Fm* values were similar at 70 and 120 μmol m−2 s −1 (Figure 5a). Plants grown under the HPS light type had similar values of *Fv*/*Fm* at 20 and 30 μmol m−2 s −1. Plants grown under the CoeLux® light type had significantly higher *Fv*/*Fm* values than plants grown under the HPS light type at 30 and 70 μmol m−2s −1 (Figure 5a). The PSII operating efficiency in the light (ΦPSII) was not different among different The anthocyanin concentration decreased with the increase in light intensity independently of the light type considered (Figure 4c). In the case of plants grown under the CoeLux® light type, the highest and the lowest values were found for 20 and 30 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> and 70 and 120 µmol m−<sup>2</sup> s −1 , respectively. In the case of plants grown under the HPS light type, the highest values were found for 20 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> and the lowest values for 70 and 120 µmol m−<sup>2</sup> s −1 . No significant difference was observed between plants grown under the CoeLux® and the HPS light type, independently of the light intensity considered (Figure 4c).

light intensities for plants grown under the CoeLux® light type (Figure 5b). In the case of plants grown under the HPS light type, ΦPSII slightly increased with the increase in the light intensity, with the highest and lowest values measured at 20 and 120 μmol m−2s −1 , respectively (Figure 5b). Plants grown under the CoeLux® light type at 20 and 30 μmol m−2s −1 had significantly higher ΦPSII values than plants grown under the HPS light type (Figure 5b). The Non-Photochemical Quenching (NPQ) for plants grown under the CoeLux® light The maximum quantum efficiency of PSII photochemistry (*Fv*/*Fm*) increased with the increase in the light intensity independently of the light type considered (Figure 5a). In the case of plants grown under the CoeLux® light type, *Fv*/*Fm* values were similar at 70 and 120 µmol m−<sup>2</sup> s −1 (Figure 5a). Plants grown under the HPS light type had similar values of *Fv*/*Fm* at 20 and 30 µmol m−<sup>2</sup> s −1 . Plants grown under the CoeLux® light type had significantly higher *Fv*/*Fm* values than plants grown under the HPS light type at 30 and 70 µmol m−<sup>2</sup> s −1 (Figure 5a).

type was not different among different light intensities at 30, 70, and 120 μmol m−2s −1 , while a significantly lower value was observed at 20 μmol m−2s −1. In the case of plants grown under the HPS light type, NPQ increased with the increase in light intensity, with The PSII operating efficiency in the light (ΦPSII) was not different among different light intensities for plants grown under the CoeLux® light type (Figure 5b). In the case of plants grown under the HPS light type, ΦPSII slightly increased with the increase in the light intensity, with the highest and lowest values measured at 20 and 120 µmol m−<sup>2</sup> s −1 , respectively (Figure 5b). Plants grown under the CoeLux® light type at 20 and 30 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> had significantly higher ΦPSII values than plants grown under the HPS light type (Figure 5b).

The Non-Photochemical Quenching (NPQ) for plants grown under the CoeLux® light type was not different among different light intensities at 30, 70, and 120 µmol m−<sup>2</sup> s −1 , while a significantly lower value was observed at 20 µmol m−<sup>2</sup> s −1 . In the case of plants grown under the HPS light type, NPQ increased with the increase in light intensity, with the only exception of 30 µmol m−<sup>2</sup> s −1 , which was the lower value, while the highest value was observed at 120 µmol m−<sup>2</sup> s −1 . Plants grown under the CoeLux® light type at 20 and 70 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> had significantly lower NPQ values than plants grown under HPS light type.

the only exception of 30 μmol m−2s

was observed at 120 μmol m−2s

μmol m−2s

**Figure 5.** (**a**) Maximum quantum efficiency of PSII photochemistry (*Fv*/*Fm*), (**b**) PSII operating efficiency in the light (ΦPSII), and (**c**) non-photochemical quenching (NPQ) for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean. **Figure 5.** (**a**) Maximum quantum efficiency of PSII photochemistry (*Fv*/*Fm*), (**b**) PSII operating efficiency in the light (ΦPSII), and (**c**) non-photochemical quenching (NPQ) for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean.

The net photosynthetic rate (Pn) increased with the increase of the light intensity independently of the light type considered (Figure 6a). For plants grown under both Coe-Lux® and HPS light type, the highest and lowest Pn values were measured at 120 and 20 μmol m−2s −1, respectively (Figure 6a). At 20 and 30 μmol m−2s −1, negative photosynthetic values were measured due to the glass delimiting the instrument cuvette chamber, which lowered the incident light received by the encapsulated leaf of 52.9 ± 7.3 μmol m−2s −1 . Plants grown under the CoeLux® light type had significantly lower Pn values than plants grown under the HPS light type at 20, 70, and 120 μmol m−2s −1 . The evapotranspiration rate (ET) for plants grown under the CoeLux® light type de-The net photosynthetic rate (Pn) increased with the increase of the light intensity independently of the light type considered (Figure 6a). For plants grown under both CoeLux® and HPS light type, the highest and lowest Pn values were measured at 120 and 20 µmol m−<sup>2</sup> s −1 , respectively (Figure 6a). At 20 and 30 µmol m−<sup>2</sup> s −1 , negative photosynthetic values were measured due to the glass delimiting the instrument cuvette chamber, which lowered the incident light received by the encapsulated leaf of 52.9 <sup>±</sup> 7.3 <sup>µ</sup>mol m−<sup>2</sup> s −1 . Plants grown under the CoeLux® light type had significantly lower Pn values than plants grown under the HPS light type at 20, 70, and 120 µmol m−<sup>2</sup> s −1 . *Plants* **2021**, *10*, x FOR PEER REVIEW 7 of 15

−1, which was the lower value, while the highest value

light type at 20 and 70

light type were

−1. Plants grown under the CoeLux®

−1 had significantly lower NPQ values than plants grown under HPS light type.

ues were found at 30 and 70 μmol m−2s −1. In the case of plants grown under the HPS light type, the Gs values were not different among light intensities, with the only exception of 120 μmol m−2s −1, which showed the highest values (Figure 6c). At 20 μmol m−2s −1 , the Gs value measured for plants grown under the CoeLux® light type was significantly higher than the value measured for plants grown under the HPS light type (Figure 6c). On the contrary, at 120 μmol m−2s −1 , the Gs value measured for plants grown under the HPS light type was significantly higher than the value measured for plants grown under the Coe-Lux® light type (Figure 6c). **Figure 6.** (**a**) Pn: net photosynthetic rate (μmol CO<sup>2</sup> m−2s −1), (**b**) ET: evapotranspiration (mmol m−2s −1), and (**c**) Gs: stomatal conductance (mmol m−2s −1) for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean. **Figure 6.** (**a**) Pn: net photosynthetic rate (µmol CO<sup>2</sup> m−<sup>2</sup> s −1 ), (**b**) ET: evapotranspiration (mmol m−<sup>2</sup> s −1 ), and (**c**) Gs: stomatal conductance (mmol m−<sup>2</sup> s −1 ) for different light intensities. Blue and green bars indicate data of plants grown under the CoeLux® and the HPS light types, respectively. Black asterisks indicate statistically significant differences (*p* < 0.05) between plants grown under the CoeLux® and the HPS light type within the same light intensity. Letters indicate statistically significant differences (*p* < 0.05) between plants grown under different light intensities within the same light type. Vertical boxes represent approximately 50% of the observations and lines extending from each box are the upper and lower 25% of the distribution. Within each box, the solid horizontal line is the median value, whereas the dotted horizontal line is the mean.

**3. Discussion** In our study, we used the model plant *Arabidopsis thaliana* to assess for the first time if the light spectrum and intensity of the CoeLux® 45HC lighting system could be suitable for plant growth in controlled environments. Both light quantity and quality are funda-The evapotranspiration rate (ET) for plants grown under the CoeLux® light type decreased with the increase in the light intensity (Figure 6b). The highest and lowest values were found for plants grown, respectively, at 20 and 120 µmol m−<sup>2</sup> s −1 , while intermediate

mental for plant growth and development [20]. In this context, LEDs show unrivaled ad-

peculiar constraints due to the physical effects involved in the setting up of their characteristic visual effects [4,6]. Thus, light quantity and quality cannot be adjusted like with other LED-based lighting systems currently used for plant growth [10]. We observed that the light emitted by the 45HC CoeLux® system, even inside the sunbeam, was characterized by low levels of photosynthetic active radiation (PAR). The registered values were similar to those that can be normally found in shaded environments, for example, under a dense forest canopy [21]. Consequently, even if natural sunlight's visual effects were perfectly reproduced, this artificial skylight cannot be compared to its natural counterpart in terms of light intensity. Shade-adapted plants are certainly the most suitable to grow under this lighting system, as photosynthesis is directly influenced by the amount of light

With the phenological analysis, we observed that *A. thaliana* plants grown under the

HPS light type, and this delay was independent of the light intensities considered. Moreover, this plant development delay was particularly evident at the last growth stages such as *Bolting* and *Silique* set, and it was of higher magnitude at the lowest light intensities. In

during the 100-days period analyzed in our study. Other studies also reported a 2-week flowering delay in *A. thaliana* plants grown under reduced light intensity and lowered R/FR [22]. Morphological data are in line with the phenological observations, highlighting

phological parameters analyzed, we observed a similar trend that grows with the increase

Plants have to balance the biomass allocation to leaves, stems, and roots in a way that matches the physiological functions performed by these organs. In stress situations, plants

in the light intensity but was always slightly lower with the CoeLux®

light type showed a significant delay with respect to plants grown under the

−1 could not reach the seed maturity stage

light type than with

light type on *A. thaliana* growth. In fact, for all mor-

reaching the plant's leaves [16].

particular, plants grown at 20 and 30 µmol m−2s

the negative influence of the CoeLux®

the HPS light type.

CoeLux®

values were found at 30 and 70 µmol m−<sup>2</sup> s −1 . In the case of plants grown under the HPS light type, ET values did not differ among different light intensities (Figure 6b). The ET values measured at 20 µmol m−<sup>2</sup> s −1 for plants grown under the CoeLux® light type were significantly higher than the values measured for plants grown under the HPS light type (Figure 6b). The ET values measured at 120 µmol m−<sup>2</sup> s <sup>−</sup><sup>1</sup> were significantly higher for plants grown under the HPS light type than plants grown under the CoeLux® light type (Figure 6b).

The stomatal conductance (Gs) decreased with the increase in the light intensity in the case of plants grown under the CoeLux® light type (Figure 6c). The highest and lowest Gs values were measured, respectively, at 20 and 120 µmol m−<sup>2</sup> s −1 , while intermediate values were found at 30 and 70 µmol m−<sup>2</sup> s −1 . In the case of plants grown under the HPS light type, the Gs values were not different among light intensities, with the only exception of 120 µmol m−<sup>2</sup> s −1 , which showed the highest values (Figure 6c). At 20 µmol m−<sup>2</sup> s −1 , the Gs value measured for plants grown under the CoeLux® light type was significantly higher than the value measured for plants grown under the HPS light type (Figure 6c). On the contrary, at 120 µmol m−<sup>2</sup> s −1 , the Gs value measured for plants grown under the HPS light type was significantly higher than the value measured for plants grown under the CoeLux® light type (Figure 6c).
