Abstract: A device configured to provide a value indicative of fluorescent emission from a substrate 5 having a test region is provided. The device comprises an electromagnetic radiation source configured to emit excitation radiation towards the test region to excite fluorescent emission from a fluorescent material in the test region. The electromagnetic radiation source is configured such that a variation in intensity of the excitation radiation across the test region is less than 15%. The device further comprises a sensor configured to capture a primary 10 image of the fluorescent emission, and a controller configured to modify the primary image based on calibration data and to use the modified image to obtain the value indicative of the fluorescent emission.