## 7 New Approaches to Monitoring and Optimisation of Microalgae Cultivation Systems
### RGB Sensors (Red-Green-Blue)  
RGB (red-green-blue) sensors are increasingly used in microalgae culture monitoring and provide fast, non-destructive methods for assessing the growth dynamics and physiological changes of organisms. Their functionality is based on analysing the intensity of reflected and transmitted light within three primary wavelength bands and enables the determination of parameters such as biomass concentration, changes in pigment composition, and the metabolic state of microalgae cultures. Compared to conventional spectrophotometric methods, RGB sensors are characterised by lower costs, ease of implementation, and applicability in remote monitoring systems, including Internet of Things (IoT) technologies [249].  
One of the main applications of RGB sensors in the cultivation of microalgae is the monitoring of growth based on changes in the colour of the culture medium. The growth of microalgae leads to increased light absorption in the red and blue range, combined with increased reflectance in the green range, reflecting the chlorophyll content. Devices such as the TCS3200 (ams AG, Premstatten, Austria) and its newer version, the TCS34725 (ams AG, Premstatten, Austria), are typically used for such analyses. These sensors are very sensitive to changes in colour intensity and allow calibration against reference wavelengths so that biomass growth can be accurately tracked in real time [250].  
Another important application of RGB sensors (ams AG, Premstatten, Austria) in the cultivation of microalgae is the assessment of environmental stress and changes in pigment composition, particularly chlorophyll a and carotenoid content. The AS7341 device (ams AG, Premstatten, Austria), a more advanced spectral sensor covering eight visible light bands, enables a more precise determination of pigment changes in microalgae under factors such as nutrient deficiency, oxidative stress, or excessive light exposure [251]. In the context of cultivation automation, RGB sensors are increasingly being integrated into IoT systems and robotic bioreactor control units. One example of such an implementation is the MAX44009 sensor (Maxim Integrated Products, Inc, San Jose, CA, USA), which is used in systems for monitoring photosynthetic intensity and dynamic changes in large-scale cultures due to its high sensitivity to visible light intensity and low power consumption [252].  
Thanks to integration with microcontrollers such as ESP32 (Espressif Systems Company, Shanghai, China) or Arduino (Ivrea, Italy), RGB sensors (ams AG, Premstatten, Austria) allow remote access to data and automatic adjustment of cultivation parameters, e.g., illumination intensity or nutrient medium composition [253]. RGB sensors are also used in image analysis of microalgae cultures, especially in systems that use industrial and microscope cameras. Devices such as the Raspberry Pi Camera Module V2 (Pencoed, UK), which is based on the Sony IMX219 sensor (Atsugi, Japan), enable high-resolution analysis of morphological and pigmentary changes in individual microalgae colonies [254]. The data from such systems can then be processed by artificial intelligence algorithms to classify cell condition and predict growth trends.  
To summarise, the application of RGB sensors in the monitoring of microalgae cultures is an efficient and cost-effective alternative to conventional spectrophotometric and fluorescence-based methods. Their integration into IoT systems and image analysis algorithms enables the continuous tracking of biomass growth, the assessment of environmental stress, and the optimisation of cultivation conditions. The development of RGB sensor technologies, especially with regard to higher spectral sensitivity and automated data analysis, could contribute significantly to increasing the biotechnological production efficiency of microalgae in the future.