1. A lighting device comprising: a communication unit to communicate with a wearable device having at least one camera, the communication unit to receive an image of a user's eye captured by the camera; a light emitting unit that includes one or more light emitting elements; and a controller to detect a pupil image based on the image of the user's eye and to control the light emitting unit based on the pupil image, wherein the controller includes an image processor to detect the pupil image based on the image of the user's eye and to determine a level of illumination corresponding to a size of the detected pupil image by comparing the pupil image with preset first and second reference values, wherein the image processor includes: an object detector to detect the pupil image from the image of the user's eye, an object recognizer to compare the size of the pupil image with the preset first and second reference values, and an application unit to determine the level of illumination based on a result of the comparison.