Abstract: The invention relates to a method for illumination. In the method, the light source (1) used is an electroluminescent light source comprising at least two luminescent layers (L7, L9), and the color of light formed in at least two luminescent layers (L7, L9) is substantially the same when the light is emitted from the light source (1). The invention further relates to a portable electronic device comprising a light source (1), and to an electroluminescent light source (1) comprising a first (L7) and a second luminescent layer (L9), which are arranged to emit light of substantially the same color from the light source (1).

Abstract: A display and keyboard illumination of battery-operated portable electronic devices using LEDs are provided. A flyback converter is modified into a dedicated converter suitable for using two LEDs and their diode-like operation is utilized. Firstly, a specified amount of energy of the battery voltage (Vbatt) is stored in the coil (L) of a primary circuit until, controlled by a comparator (K). The LEDs are connected in parallel with the coil, in direction such that they substantially prevent the current leaking through them. Secondly, the coil is disconnected from the battery by a switch (SW). A comparator (K) detects when the coil current reaches a specified threshold level and, by using a control circuit (SWC), then causes the switch (SW) to become non-conductive. The self-induction of the coil builds up a voltage exceeding the forward bias of the LEDs, which (thirdly) keeps on passing the current and illuminating.