The topic of the final paper is internal illumination. In order for employees to achieve the highest possible efficiency in performing their workplaces, it is necessary to pay attention to the adequate level of lighting in the workplace. For the successful participation of almost all physiological and psychological functions, man had to provide objective physical opportunities in which a man can at least a little effort and with maximum comfort earn his job and achieve success in his work. By adequately illuminating workers in the workplace, in addition to achieving greater efficiency, they achieve better work results than those working in dimly lit workplaces. In my work, I will first theoretically explain how light is created, its impact on humans, types of lighting, light sources and types of lighting. Furthermore, I will talk about my research, which will be proven in one of the business HEP-distribution system operators, and I will present data and conclusions.