X-ray is a tool used to perform medical diagnosis by emitting X-rays on the body to be diagnosed. When used, X-rays should be limited to radiation exposure doses so as not to be harmful to the patient, an exposure time setting (mA), x-ray quality setting and x-ray penetration (kV), and radiation limits (collimation) are required. The exposure limit setting aims to avoid the inaccuracy of the diagnosis causing repetition of the shots. The collimator is one part of the X-ray plane that has the function to adjust the magnitude of exposure to radiation. In this study the authors make a simulation of collimators using LED lights controlled by android OS-based applications The purpose of this research is to provide a collimator simulation tool using LED lights as a light source with wireless control using OS android based applications to facilitate the user in managing the field of X-ray exposure at a certain distance. Based on the result of the test 20 times using Lux meter, the average value of lux is 122.93 lx for radiation distance 100 cm, 106,03 lx for irradiation distance 110 cm, and 77,16 lx for 120 cm radiation distance, the result still meet the existing standards. However, at a distance of 130 cm, the average value of lux is 66.65 lx. this indicates that the tool is effective at a distance of 100-110 cm. For wireless control distance using OS android based applications, optimally used up to a distance of 1000 cm.