## 1 Introduction  
Natural light is essential for the adjustment of circadian clocks and the coordination of cellular physiology. Nevertheless, emerging evidence suggests that increased exposure to artificial light can significantly influence important characteristics of cells. It has been shown that blue light at lower doses (\(\leq\)300 mJ/cm\({}^{2}\)) triggers the synthesis of hydrogen peroxide in T-cells and affects cell motility [1]. Other studies suggest that blue light changes the redox state of the cell causing oxidative stress and alter mitochondrial activity [2; 3] or that green light can change gene expression [4]. As recent technological advances brought televisions, LEDs, and displays, blue light emitters have become a part of our everyday life and blue light is also used for polymerization of dental resin in dentistry [5], its effect on the behavior of cells should be deeply studied. Studies on model organisms suggest that visible light can exert a range of detrimental effects. For example, a single acute blue light exposure causes cell death of photoreceptors in the retina of mice and flies [6; 7]. Blue light is also used in photodynamic therapy (PDT) of cancer. PDT represents an important treatment approach as it uses a photosensitizer and visible light to induce reactive oxygen species (ROS) to kill cancer cells [8; 9]. For example, [PERSON] et al. have reported the antitumor effect of an agent dequalinium and light of a 366 nm wavelength. A combination of specific light and an agent inhibits protein kinase C and induces inhibition of metastatic behavior of melanoma cells [10]. However, the effects of blue light itself on the essential characteristic of cancer cells, such as motility or cell division is not known.  
The light with [PERSON] nm is commonly used as an excitation light in fluorescence microscopy (FM) which allows precise imaging of cellular structures or even certain molecules in cells [11; 12]. Despite the widespread of FM in cell research in the last 40 years, the impact of such techniques on basic cell features was not well characterized yet. In this study, we focused on the effect of light with [PERSON] nm wavelength on the dynamical and [PERSON] properties of the three human cancer cell lines established from different tissue (PC-3, A2780, G361) and one non-malignant human prostate cell line (PNT1A), respectively. In our experiments, we use a multimodal holographic microscope (MHM) that combines holographic microscopy with fluorescence microscopy. The MHM used in this study is based on an off-axis setup with an incoherent source of light which enables high-quality quantitative phase imaging, avoiding disruptive interferences [13]. Holographic microscopy (HM) has been demonstrated as a powerful tool for long-term and label-free imaging of cell samples in vitro, as it works on the principle of quantitative phase imaging (QPI). HM provides information about many cellular processes and parameters such as cell cycle [14], cell kinetic [15], viability [16], cell morphology [17], and cellular uptake [18]. This approach enables also to measure cell mass and its distribution in cells [19; 20; 21]. Based on QPI, a new approach of distinction of apoptosis and lytic types of cell death was developed [22; 23]. HM also enables effort-less and more accurate tracking of cells and their motility patterns compared to other microscopic techniques [24; 25]. Our study aims to present QPI and holographic microscopy as a suitable method for the evaluation of cellular morphological and dynamical parameters. The results suggest that HM within advanced image analysis is capable of correctly distinguishing between changes in cell motility, cell dry mass, cell density, and cell death induced by blue light and that the impact of light is dependent on the exposure time and light intensity.