Defective unshu oranges (Citrus reticulate Blanco var. unshu) were sorted based on fluorescent imaging technique in a commercial packinghouse but fresh appearing unshu were rejected due to fluorescence appearing on their peel. We studied the various visible patterns based on colour, fluorescence and microscopic images, where even areas of the peel that are not obviously damaged can have fluorescence, to provide a categorization of fluorescence reasons. The categorization corresponded to: 1) hole and flow; 2) influenced by damaged or rotten fruits that have released peel oil onto it; 3) immature or poor peel quality; 4) whitish fluorescence due to agro-chemicals and 5) variation of the growing season. The identification of such patterns of fluorescence might be useful for citrus grading industry to take some initiatives to make the entire automated system more efficient.