# Propagation of Inoculum for _Haematococcus pluvialis_
## 4 Discussion
The diodes not only have low power consumption, but they also guarantee the correct light spectrum, which corresponds with the spectra of photosynthetic absorption of microalgae. They also allow for smooth control over the intensity of illumination [29]. LED strips were mounted in four corners of each station and connected to the drivers equipped in PWM (pulse-width modulation) outputs. It enabled to proportionally control the LED illumination intensity in the range of 0-100% of power using a standard analog signal of 0-10 V. Thanks to that system, the operator was allowed to run the LED lighting using the power of his choosing. The described system for propagation of inoculum was supposed to be characterized by the lowest level of complexity. Thus, only two basic types of sensors were used along with the option to dose air and carbon dioxide, and the least complicated lighting system, which uses LED diodes of one type, and color. Admittedly, the use of blue light has a positive influence on increasing the size of cells and red light improves cell division rate. However, in this case, a decision has been made to use warm white light in the inoculation module because other wavelengths of the light are needed for the correct cell metabolism and maintaining high cell activity [29]. We chose the warm white LED diodes because the wavelength of light that they generate is the closest to the natural sunlight with the predominance of red color. This compromise solution supports the intensification of the inoculate propagation without complicating the lighting system. The results of the experiments, which were the confirmation of choosing the correct type of lighting, studied the influence of the color of LED lighting on the productivity of microalgae cultivation in the airlift type photobioreactor [30]. Among the following colors of lighting: blue, orange-red, deep red, sunlight, yellow, and warm-white, the highest productivity of cultivation was achieved using yellow and warm-white light. However, in the case of yellow lighting, the authors used blue-light supplementation to stimulate typical growth and increase productivity [30]. The primary task set before the described station was the preparation of a suitable amount of inoculate needed for inoculating of the system comprising of six 90 dm\({}^{3}\) volume photobioreactors each. Biomass concentration in the range 1.40-1.99 g/dm\({}^{3}\) (Figure 8) was obtained on the eighth day of conducting experiments was decidedly higher than the one reported by [PERSON] et al. [31]. Depending on the used culture media after the eighth day of the cultivation, they have obtained biomass concentration within the range of about 0.73-0.93 g/dm\({}^{3}\). The experiments were carried out, similarly to the ones conducted in AlgaeLabs (cf. the beginning of the Results chapter), in 5 dm\({}^{3}\) glass tanks. However, it is necessary to take into consideration the fact that, in their research, they have used a different strain of _H. pluvialis_, and the experiments started with a constant content of microalgae biomass at the level of 0.15 g/dm\({}^{3}\). The volume of biomass was significantly lower than in the presented experiments where the starting volume of biomass was taken on the value within a range of 0.42-0.78 g/dm\({}^{3}\). When conducting experiments in a glass column photobioreactors, also the ones with _H. pluvialis_ microalgae, the maximum specific growth rate was reached at the initial volume of biomass at 0.5 and 0.8 g/dm\({}^{3}\)[32; 33]. The final value reached over the course of experiments is similar to the results obtained in [PERSON] et al. [34], which aimed at comparing the influence of different light intensities on the growth of the _H. pluvialis_ biomass. The experiment was conducted in aerated glass photobioreactors, a working volume of 0.7 dm\({}^{3}\), and an initial cell density of 0.3 g/dm\({}^{3}\).