Transillumination is the shining of a light through a body area or organ to check for abnormalities. The room lights are dimmed or turned off so that the area of the body may be seen more easily. – A bright light is then pointed at that area. This test may be done along with other tests to diagnose: hydrocephalus in newborns or infants, hydrocele in males, breast lesions or cysts in females. – In general, transillumination is not an accurate enough test to rely on. Further tests, such as an x-ray, CT, or ultrasound, are needed to confirm the diagnosis.