VeRelief has 20 discrete intensity levels, ranging from 0-16mA of current.
As you notice, there are only 5 LED lights on the front display panel. This means there are 4 discrete intensity levels on each LED light, and you would have to click the intensity button at least 4 times to get to the next LED light.
Each time you click the intensity level, the LED light will get a little bit brighter. This can be hard to notice as the increase in light is faint, but you can trust that it is occurring. Once you click it at least 4 times, the next LED light will turn on.
Note
It is important to understand that everyone will experience the stimulation at a different intensity level. Therefore you don't need to pay too much attention to how many LED lights are turned on because all that matters is that you turn up the intensity as high as you can comfortably tolerate.