A digital-imaging based code symbol reading system comprising an image sensing array with a field of view (FOV), an illumination subsystem with an LED illumination array, an automatic illumination measurement subsystem, an illumination control subsystem, and programmed imager processor supporting an image-processing based illumination metering program. The automatic illumination measurement subsystem, employing a photodetector operating independently from the image sensing array, is used to automatically measure the illumination level at a particular region of the FOV and determine the illumination duration necessary to achieve a desired spatial intensity in the detected digital image. The illumination metering program automatically analyzes and measures, in real-time, the spatial intensity distribution of the digital image and determines whether or not a corrected illumination duration is required or desired when detecting the next or subsequent digital images, during the current or subsequent object illumination and imaging cycle. The previously determined illumination duration is over-written with the corrected illumination duration, which is used to drive the illumination subsystem and form and detect subsequent digital images of the illuminated object.