Many photosensitive materials used in technical and industrial applications, such as photoresist, are sensitive only to blue, violet, and ultraviolet light and may be handled under a brighter yellow safelight. Low-pressure sodium vapour lamps sometimes are used in larger industrial darkrooms. They emit nearly monochromatic light at 589 nm (yellow), to which the materials are insensitive; as a result they can be extremely bright while still "safe".[citation needed]