High pressure sodium lamps produce an intense pinkish-white light with a colour temperature of 2050°k from an arc discharge in high pressure sodium vapour and are an efficient way of lighting large areas. Succulent plants grow well under this light, but the colour cast may reduce acceptability for decorative illumination. The standard lamps are said to encourage production of flowers and fruit. Versions producing more blue light are available to promote compact vegetative growth, but this is not needed if the lamps are used to augment natural daylight which provides sufficient blue light.. Special starter circuits are required. Check that lamps will operate in a horizonal position if this is required