A method for controlling electrical light sources, in particular, light-emitting diodes (LEDs) by pulse width modulation of a supply voltage is disclosed, whereby the supply voltage or a parameter dependent thereon, for example the current or the electrical power, is measured and the pulse width is controlled as a function thereof. According to the invention, for the light source a characteristic curve for the brightness is generated as a function of the supply voltage or the parameter dependent thereon and, from the measured supply voltage or the parameter dependent thereon, an actual brightness value is determined with the characteristic curve and is compared with a given brightness value and the pulse width controlled as a function thereof.