There are widely used computers in agricultural mobile technique, which show important parameters of work process and its quality in. It is important a good illumination of workplace for quick and correct information identification from the VDT’s. There are forming different levels of illumination in agricultural technique cabins when they are working at the field. Those levels are fluctuating and operator’s eye should adapt to them compulsory. Operator’s vision feels fatigue because of those processes and work becomes not so effective. There are assessed in the work, that luminance increase on the VDT screen, as do illumination level in the cabins of agricultural mobile technique and as a result of this process, contrast reduces and visibility become worse. In experiment, there was researched, that tasks were performed quicker, when illumination was 300 -500 lx, and slower, when - 900-1200 lx. There are assessed the response time dependence on illumination level model , which helps to calculate the duration of operator’s watching, which influences the results of work quality and safety.