1. A method for sensing a motion of an object, said method to be implemented by a motion recognition device that includes an image acquiring unit, a processor, and at least one lighting module for providing a light source, said method comprising the following steps of: a) configuring the image acquiring unit to acquire continuously a series of image frames by detecting intensity of light received thereby; b) configuring the processor to receive at least one of the image frames from the image acquiring unit; c) configuring the processor to: compute, from at least one of the image frames received in step b), a first luminance value that is associated with ambient light; compare the first luminance value with a first predetermined threshold value; and select a first operation mode when the first luminance value is smaller than the first predetermined threshold value; d) when the first operation mode is selected in step c), configuring the processor to generate a control signal for activating the lighting module, and to determine whether an object is detected by the following sub-steps of: d11) configuring the image acquiring unit to acquire at least one image frame; d12) configuring the processor to compute a second luminance value according to said at least one image frame acquired in sub-step d1); d13) configuring the processor to compare the second luminance value with a second predetermined threshold value; and d14) when it is determined in sub-step d13) that the second luminance value is larger than the second predetermined threshold value, configuring the processor to determine that the object is detected in said at least one image frame acquired in sub-step d1); and e) when it is determined in sub-step d14) that the object is detected, configuring the processor to receive the image frames from the image acquiring unit, and to determine a motion of the object with respect to a three-dimensional coordinate system according to the image frames thus received.