A display for an electronic device may be calibrated and corrected for pixel-to-pixel variations in intensity. Radiation-sensing elements used for the calibration are not incorporated as circuit elements within the pixel circuits and may lie outside the pixels. Waveguides, reflectors, or the like may be used to optically couple the radiation-emitting elements of the pixels to the radiation-sensing elements. The radiation-sensing elements may be part of an apparatus separate from the electronic device or may be embedded within the electronic device. Many different methodologies may be used for correcting intensities to achieve better homogeneity in intensity among the pixels within a display.