The definition of ingress protection (IP) rating is a classification that must be declared by the manufacturer for both the LED drivers and all other electronic devices. This definition indicates how the electronic circuits have protection against water, dust, and other solid objects. Therefore, the requirements of this declared definition must be met. In this paper, this class definition for the LED driver circuits used in street lighting is declared as IP66. In order to ensure IP66 class protection requirements, the LED driver circuit is placed in a closed box. However, since the box is completely closed, the heat cannot be transferred sufficiently to the outside, even if the box is made of thermally conductive aluminum material. This may cause the LED driver circuit to malfunction. Therefore, in order to fulfill the IP class requirement and to contribute to the solution of the temperature problem, the box of the driver card is filled with a thermal-conductive potting material. However, this filling material can contribute to the solution of thermal problems, but also has a number of drawbacks. In this paper, the effect of the potting material on LED driver circuits to reliability and electromagnetic compatibility performance is investigated experimentally and comparatively.