Methods and apparatus are provided for identifying the presence of leaks in a fluorescent bulb or other lamp suitable for use as a backlight in an avionics or other liquid crystal display (LCD). The lamp is first placed in a bath of helium or another vaporous substance having relatively small molecular size. The vaporous material is allowed to permeate through any leaks that may exist in the lamp and to thereby intermix with the light-producing vaporous material contained within the channel of the lamp. The lamp is removed from the bath and subsequently operated (e.g. at a low intensity), and the output electrical or optical characteristics of the lamp under test are obtained. If the output characteristics of the lamp under test substantially correspond to characteristics obtained from a lamp that is known to be in proper working order, then the absence of leaks in the lamp under test can be presumed.