*3.1. Specific Growth Rate and Biomass Productivity*

The dry weight, specific growth rate, and productivity of *I. zhangjiangensis* under different light conditions are shown in Table 1. The highest and lowest accumulated biomass (dry weight) were observed in the microalgae cultured under the white and red lights, with 1.1761 ± 0.0212 and 0.5683 ± 0.0284 g/L, respectively. Significant differences were observed among all the specific growth rate values of *I. zhangjiangensis* cultured under different illumination conditions. The specific growth rates from the highest to the lowest values were under the red, blue, white, and green lights, with 0.4431 ± 0.0055, 0.4089 ± 0.0029, 0.2948 ± 0.0011, and 0.2466 ± 0.0035 *μ*/day, respectively.

**Table 1.** Growth parameters of *I. zhangjiangensis* cultured under different colored LEDs.


Note: Different lowercase letters represent significant differences between different colored LEDs at the same culture time (*p* < 0.05).

The highest productivity value, a parameter related to potential large-scale microalgae production systems, was observed under the white light (0.0728 ± 0.0013 g/L/day) and was significant when compared to the values observed under the red and blue lights (0.0620 ± 0.0032 and 0.0617 ± 0.0018 g/L/day, respectively). Low values were observed under the green and yellow lights, with 0.0490 ± 0.0032 and 0.0390 ± 0.0028 g/L/day, respectively.

#### *3.2. Algal Growth*

The daily mean growth of the microalgae *I. zhangjiangensis* cultured under the five different colored LEDs was calculated. The stationary phase was attained after the 11th day from the inoculation in most of the treatments (different light colors), and significant differences were observed when microalgae density values (cells/mL) were compared at their respective stationary phases (Figure 1). The microalgae cultured under white light exhibited a pause in its growing tendency on day 9, but on day 13 resumed exponential cell proliferation until day 18 at the highest value (1100.0 × 104 cells/mL). A similar growth pattern was observed in the microalgae cultured under the blue light when cell proliferation paused on day 9 and resumed on day 14, reaching 502.1 × 104 cells/mL. The microalgae cultured under the green light also exhibited a lag on day 12, but resumed on day 15, reaching maximum cell density, 755.0 × <sup>10</sup><sup>4</sup> cells/mL, on day 17. The microalgae that were cultured under the red light reached the stationary phase on day 10 but exhibited the lowest cell density, 0.4 × 107 cells/mL, among all treatments.

#### *3.3. Photosynthetic Pigment Production*

Significant differences were observed among the maximum Chl-*a* values at the stationary phase of the different treatments (Figure 2). The maximum Chl-*a* value, 1.473 ± 0.037 mg/L, was observed after day 18 of culture under green light. Microalgae cultivated under white light exhibited the second highest value, 1.073 ± 0.108 mg/L, on the 21st day. The red light initially exhibited low levels, but after the 9th day of cultivation, its growth accelerated and exhibited the third Chl-*a* value, 0.873 ± 0.007 mg/L, on the 11th day. The Chl-*a* values under yellow and blue light were 0.693 ± 0.008 and 0.675 ± 0.002 mg/L, respectively, and were the lowest levels of Chl-*a* concentration among all the treatments.

*p* < 0.05 *t*-test).

**Figure 2.** Daily mean values of chlorophyll-*a* in *I. zhangjiangensis* cultured under different colored LEDs (n = 3, *p* < 0.05 *t*-test).

The Chl-*b* levels in the five different colored LEDs are shown in Figure 3, and significance was observed at the maximum levels attained among treatments. The maximum Chl-*b* level, 1.504 ± 0.001 mg/L, was observed on the 21st day of culture under the green light. The white light evoked the second highest value (0.918 ± 0.001 mg/L), occurring the same day as the green light. The orange, red, and blue lights evoked lower Chl-*b* levels, with values of 0.360 ± 0.001, 0.275± 0.009, and 0.232 ± 0.003 mg/L, respectively.

The total Chl concentrations of the microalgae *I. zhangjiangensis* cultured under the five different colored LEDs are shown in Figure 4. In the case of the green and white lights, the highest levels were observed on day 21, with values of 2.827 ± 0.083 and 2.238 ± 0.083 mg/L, respectively. Under the red, yellow, and blue lights, the highest mean total values were observed within the 11th and 13th days of cultivation, with corresponding values of 1.095 ± 0.002, 1.000 ± 0.002, and 0.872 ± 0.049 mg/L, respectively.

**Figure 3.** Daily mean values of chlorophyll-*b* in *I. zhangjiangensis* cultured under different colored LEDs (n = 3, *p* < 0.05 *t*-test).

**Figure 4.** Daily mean values of total chlorophyll in *I. zhangjiangensis* cultured under different colored LEDs (n = 3, *p* < 0.05 *t*-test).

#### *3.4. Protein and Soluble Carbohydrates' Production*

Significant differences were observed in the total protein content of *I. zhangjiangensis* grown under different light colors (Table 2). A particularly high content (524.1935 ± 6.5846 mg/L) was observed in the microalgae cultured under the white light. No significance was observed between the blue and yellow lights, in which both lights exhibited lower content than in the white light. The microalgae cultivated under green and red lights observed the lowest values.


**Table 2.** Protein and carbohydrate content in *I. zhangjiangensis* cultured under different colored LEDs.

Note: Different lowercase letters represent significant differences between different colored LEDs (*p* < 0.05).

The mean values of the carbohydrate content were also significant among all light color qualities (Table 2). The highest mean value was 24.4697 ± 0.0206 mg/L, observed in the microalgae cultured under blue light. The green, red, white, and yellow lights exhibited significant mean values within them, varying from 7.8455 ± 0.1247 to 9.3687 ± 0.0206 mg/L.
