Definitions for "Longwave"
A wavelength of ultraviolet light. Some minerals display fluorescence when exposed to longwave ultraviolet light. Commonly abbreviated as LW.
Lasers or LEDs that emit light with wavelengths around 1300nm. When using single mode (9nm) fibre, longwave lasers can be used to achieve lengths greater than 2Km.
frequencies usually at 300khz or lower, although longwave can also mean anything below 530khz. (see beacons above)