An eye tracking apparatus comprising: - an illumination device (200, 220), configured to illuminate a user's eye when the user is using the eye tracking apparatus; - at least one sensor configured to obtain information on the user's eye by imaging the user's eye when the user is using the eye tracking apparatus, and - at least one processing core configured to determine a direction of the user's gaze based on the information on the user's eye and based on an indication of place and orientation of the illumination device (200, 220) with respect to the at least one sensor, wherein the at least one processing core is configured to determine the indication based on the information on the user's eye, wherein either A or B of the following applies: A) the illumination device (200, 220) comprises at least three light sources (202, 222) disposed in the illumination device (200, 220) such that distances between consecutive ones of the at least three light sources (202, 222) are not equal, enabling determination of the orientation of the illumination device (200, 220) based on glints of the at least three light sources (202, 222) on a surface of the user's eye, and B) the illumination device (200, 220) comprises at least two light sources (202, 222), the light sources (202, 222) comprising light sources (202, 222) of different size and/or shape, enabling determination of the orientation of the illumination device (200, 220) based on glints of the light sources (202, 222) on a surface of the user's eye, characterized in that the at least one processing core is further configured to receive the indication from the illumination device (200, 220), the illumination device (200, 220) comprising at least one of a position-detecting sensor, an acceleration sensor and a rotation-detecting sensor. - an illumination device (200, 220), configured to illuminate a user's eye when the user is using the eye tracking apparatus; - at least one sensor configured to obtain information on the user's eye by imaging the user's eye when the user is using the eye tracking apparatus, and - at least one processing core configured to determine a direction of the user's gaze based on the information on the user's eye and based on an indication of place and orientation of the illumination device (200, 220) with respect to the at least one sensor, wherein the at least one processing core is configured to determine the indication based on the information on the user's eye, wherein either A or B of the following applies: A) the illumination device (200, 220) comprises at least three light sources (202, 222) disposed in the illumination device (200, 220) such that distances between consecutive ones of the at least three light sources (202, 222) are not equal, enabling determination of the orientation of the illumination device (200, 220) based on glints of the at least three light sources (202, 222) on a surface of the user's eye, and B) the illumination device (200, 220) comprises at least two light sources (202, 222), the light sources (202, 222) comprising light sources (202, 222) of different size and/or shape, enabling determination of the orientation of the illumination device (200, 220) based on glints of the light sources (202, 222) on a surface of the user's eye, characterized in that the at least one processing core is further configured to receive the indication from the illumination device (200, 220), the illumination device (200, 220) comprising at least one of a position-detecting sensor, an acceleration sensor and a rotation-detecting sensor.