Lamp control

A user device (200) comprising a display (206), an interface (208) for communication with a lamp comprising controllable light sources (104) and a processor (202) configured to run an application (214), wherein the application is configured to: control the lamp to emit light in accordance with a source light pattern (302), said source light pattern defining for each light source the light that is to be emitted by the light source and designating at least one of the light sources as a marker light source (308); receive an image of the source light pattern as projected onto a target surface (300) by the lamp wherein the image is captured by a camera (210), wherein the target light pattern (310) in the image is distorted; display the received image on the display; detect locations in the displayed image where the marker light source(s) are positioned/intended to emit light onto the target surface; and use the detected locations of marker light source(s) to align a control overlay over the displayed image, the control overlay identifying for each light source an area in the displayed image where the light source is intended to emit light onto, wherein the control overlay enables a user of the user device to control the light sources in response to at least one user selection.