## 1 Introduction  
Microalgae are ubiquitous photosynthetic microorganisms that consume CO\({}_{2}\), light, and inorganic nutrients to produce biomass, which is rich in compounds such as lipids, carbohydrates, proteins, and pigments [1]. The biochemical composition of the microalgae varies according to the nature of the microalgae, the cell density, the growth phase, and the culture conditions, such as temperature, pH, salinity, CO\({}_{2}\) concentration, medium composition, and light intensity [2]. Light and temperature are important factors for algae growth [3]. It has been observed that there are species-dependent requirements for optimal growth and metabolite accumulation, e.g., _Chorella pyrenoidosis_ requires an optimal daytime temperature of 31 \({}^{\circ}\)C and an illumination of 420 \(\upmu\)mol\({}_{\text{hv}}\).m\({}^{-2}\)s\({}^{-1}\), with a photoperiod of 16:8 h light:dark for maximum biomass and lipid production [4]. However, there is much evidence that the specific growth rate increases dramatically with rising light intensity, up to a certain limit, followed by an immediate decrease after this saturation limit is achieved [5]. The study of algae cultivated under different light regimes reveals that continuous light is best for optimal growth rate and biomass production. [PERSON] et al., 2012 proved that growing _Chlamydomonas reinhardtii_ cc124 in a 12 h:12 h photoperiod regime reduced both the algal growth rate and the cell density by approximately 30% compared to continuous light conditions [6]; [PERSON] et al., 2012 observed that _Botryococcus braunii_ KMITL cultivated under a 24:0 light:dark cycle produced four times as much biomass than that generated under a 12:12 h light:dark regime [7]. Light intensity and regime can affect the biochemical composition; an increase in TAG accumulation from 1.5% to 12.4% w/w was observed in the biomass produced by _Neochloris oleoabundans_ cultivated under excess light absorption, and with a limited nitrogen supply [8], and the carotenoid content was monitored under high irradiance. This revealed an increase in all carotenoids for _Allocasuarina torulos_, while a specific increase in mainly zeaxanthin and myxoxanthophyll was observed with _Nostoc_ sp., and myxoxanthophyll and \(\beta\)-carotene with _Anabaenopsis elenkinii_[9]. However, increasing the light intensity led to irreversible damage to the algae cells, such as with _Chlamydobotrys_ stellate and _Chlamydomonas reinhardtii_ which showed irreversible damage when the photon flux density was increased from 50 to 1500 \(\upmu\)mol\({}_{\text{hv}}\).m\({}^{-2}\)s\({}^{-1}\), and from 150 to 5000 \(\upmu\)mol\({}_{\text{hv}}\).m\({}^{-2}\)s\({}^{-1}\), respectively [10]. Temperature is also a crucial factor which affects both growth and biochemical composition of microalgae. Growth rate, biomass, and evolution in biochemical composition were studied in depth at various constant temperatures for several microalgae isolates. [PERSON] et al. observed that total lipid accumulation increased at a higher rate in _Isochrysis galbana_ at 30 \({}^{\circ}\)C, and the proportion of non-polar lipids decreased slightly [11]. However, it was observed that extreme temperature might have a negative effect on algae physiology. [PERSON] demonstrated that increasing the temperature to 42 \({}^{\circ}\)C for 15 min reduced the formation of _Chlorella vulgaris_ autospore mother cells [12], while doubling the time increased it from 8.6 \(\pm\) 0.6 h to 48.5 \(\pm\) 2.6 h when the cultivation temperature was reduced from 27 \({}^{\circ}\)C to 5 \({}^{\circ}\)C [13]. The same authors joined [PERSON] et al., in hypothesizing that low temperatures may reduce the rate of photosynthesis [14]. Although the effects of constant temperature on metabolism are widely recognized, diurnal temperature fluctuation is also shown to have a significant impact on algae growth and biochemical composition.