## 4 Discussion  
Diatoms have been suggested as potential high value molecule suppliers for nutraceutical, fuel and aquaculture sectors, by providing bioenergy, food and feed and as support of wastewater bioremediation [3]. They are fast growing organisms and require  
Figure 10: Canonical Analysis of Principal (CAP) components of the _P. tricornutum_ cultures (\(N=5\)) subjected to the three light treatments, having as basis the TAG fatty acid profile (relative concentrations) at the end of the 96 h exposure period (100% classification efficiency). Figure 9: TAG fatty acid profile (**a**) saturation classes (**b**) and cellular content (**c**) of the _P. tricornutum_ cultures (\(N=3\)) subjected to the three light treatments at the end of the 96 h exposure period (average \(\pm\) standard error, letters denote significant differences between light treatments at \(p<0.05\)). low cultivation conditions while offering high process turnover and economically viable processing alternatives [2]. The current study reports that pigment and fatty acid profiles in the model diatom _Pineodactylum tricornutum_ can be modulated based on different spectral light regimes supplied through LEDs without limiting cell division rates. At this level, the application of RGB LED illumination versus red and Blue LED illuminations did not lead to different cell densities at the end of the 96 h culture period. Such similarity in cell density at the end of the culture trials might be due to the nutritional limitation in the late phase of the culture, regarded to the high division rates common in the species _P. tricornutum_[41]. However, cultures exposed to red LED illumination presented a faster growth during the first 48 h, indicating a potential role of the light conditions for exponential phase cell growth enhancement. As all light treatments were adjusted to the same total photon flux rates, increased growth during the first days of culture may therefore indicate improved light harvesting under Red LED illumination. Previous studies showed an enhancement of microalgae cell growth cultured under blue light illumination [42] due to higher photosynthetic electron transport, while blue light may also induce higher nonphotochemical quenching [43]. Although most diatom pigments have higher absorption rates for shorter wavelength of light (blue light), at this level no higher growth rates were observed, indicating that given photon flux densities were sufficient to obtain maximum cell density growth. Excessive energy might then be dissipated along the photosynthetic transport chain, limiting accumulation of biomass [44]. When photosynthetic efficiencies are compared to RGB illumination, no apparent differences occur at the end of the experiment. However, when cell growth is compared based on pigment weighted light absorption, some differences become obvious. The cells grown under red LED illumination have higher \(Q_{phar}\) photosynthetic efficiency concomitant with the higher growth rates as observed during the first 48 h. This is due to the differences in the light absorption of the different pigment profiles originating from the different light quality exposure. This might be due to the high chlorophyll \(a\) content, a pigment with a high absorption coefficient at 627 nm (equals red LED dominant wavelength) [30]. In terms of phenomenological energy fluxes the cells grown under red LED illumination showed a reduction in all energy fluxes in a proportional manner, indicating that there is a higher efficiency in the incident light-use. This was in fact previously reported [17], where _P. tricornutum_ cells grow under red light showed lower nonphotochemical quenching (lower energy dissipation) and thus higher light-use efficiencies per incident photon. This is also in accordance with the higher dissipated energy flux rates (concomitant with higher nonphotochemical quenching, as reported in [17]) observed in the cells grown under Blue LED illumination.