Low Pressure Sodium is a monochromatic light source. Colors aren't
discernible under this type of lighting. These lamps appear yellow with a slight pinkish tint. The poor color properties of this lamp make it impractical for use in
applications other than street lighting or lighting for safety and security. It's
used almost exclusively in outdoor applications.
Aside from its excellent energy efficiency, this source has another important advantage. It has been used a great deal in areas that are sensitive to light pollution. Arizona and southern California have used Low Pressure Sodium lamps extensively because the monochromatic light doesn't interfere with astronomical observation. Low Pressure Sodium light also provides good fog penetration.
