Constantly growing demand for electrical energy compels for energy efficient electrical equipment. In lighting this assumes utilization of energy effective and intellectual lighting technologies. LED lighting technology combines both of these two ways. LED elements always require some electronic ballast that may consist of a primary power supply and a number of secondary dimmers for light regulation. These circuits can be implemented as DC/DC converters. In the paper buck and boost dimmers have been investigated from the point of view of their losses, weight and size. In has been found that buck converter can be the smaller and operate with the smaller losses. Higher switching frequency is preferable while the power switches of the dimmer have to be used with reasonable heatsinks. Larger values of inductance may reduce the total dimensions in spite of additional size due to the bigger coils. Ill. 13, bibl. 6, tabl. 5 (in English; abstracts in English and Lithuanian).