A method (300) for measuring illumination by a lighting unit (10) of a target surface (50) within a lighting environment (100) includes the steps of: illuminating (320), with a light source (12) of the lighting unit, the target surface; detecting (330), with a light sensor (32), a light intensity for a plurality of locations of the target surface; detecting (340) parameter of the lighting environment; selecting (350), by a controller of the lighting unit, a subset of the plurality of light intensities based on the detected parameter of the lighting environment; and estimating (360), using the selected subset of light intensities, a lux of the target surface.